Upcoming Events:

Huijun Han

Affiliation: Ulsan National Institute of Science & Technology (UNIST)

Research Interests:  Atomic scale investigation on ion-water interaction, Charge-dependent properties of atoms and molecules

Title: Salt dissolution at atomic scale

Abstract: Ion-water interactions are fundamental to electrochemistry, catalysis, battery, and biology. However, conventional experiments in aqueous solutions at the macroscopic level averages out hydration numbers, structures, and effective charges of ions. Recent studies using scanning tunneling microscopy present an atomic view of the hydration and transport of Na+ ion [1] as well as the specific ion effect on hydration structures [2,3]. Despite these advances, the microscopic understanding of salt dissolution in water–one of the simplest and well-established reactions–has remained elusive due to the statistical ensemble of aqueous solutions. In this talk, I will discuss the atomic-scale investigation on the salt dissolution, by controlling a single water molecule (H2O) at an under-coordinated site of a sodium chloride (NaCl) [4]. Precise manipulation of H2O molecules on NaCl surface provides the insight into ion-water interactions and the surface dynamics of the molecules, which are responsible for the selective dissolution of anions in real space. Our results indicate that the polarizability difference between Na+ and Cl− ions contributes to the bond characteristic and cleavage of the ionic bonds by one H2O molecule. The water dipole attracts an electron cloud of Cl− ion engaging in the ionic bonds, weakening the bond strength and facilitating the dissolution of the Cl− ion. This study provides the microscopic mechanism of the salt dissolution.

Rohit Kishan Ray

Affiliation: IBS Center for Theoretical Physics of Complex Systems

Research Interests: Steepest entropy ascent, Thermalisation,Quantum Foundation, Entropy, Many-Body Localisation

Title: Fourth Law of Thermodynamics: Application to finite dimensional systems

Abstract: In this talk, I will give an overview of the steepest entropy ascent (SEA) formalism, also known as the fourth law of thermodynamics. I will begin by introducing some preliminaries of the SEA, and then will follow up with results for some finite dimensional quantum systems including single qubit, single quantum walker, and two fermionic quantum walkers. I will conclude the talk by discussing about the future directions with this theory.

Niccolò Fontana

Affiliation: University of Oxford

Research Interests: Molecular Magnetism

Title: Coherent Control of Spin Systems using DC and AC Electric Fields

Abstract: Spin-based quantum systems offer a rich platform for exploring quantum phenomena and potential applica- tions in quantum information processing [1, 2]. The standard method for manipulating and detecting spin states uses microwave pulses resonant with spin transitions via magnetic fields. However, local magnetic control and readout of spin states in devices face challenges due to unwanted crosstalk and the difficulty of confining magnetic fields to the nanoscale. Since electric fields can be localized more easily, electrically controlling spins offers a promising solution to this limitation [3, 4]. In this talk, I will focus on three experiments demonstrating the coherent control of spin systems using both DC and AC electric fields. First, we explore the DC-electric control of a photogenerated, spin-polarized state embedded in a molecular semiconductor that exhibits low spin-orbit coupling—a property typically deemed essential for effective electric field manipulation. Next, we delve into the implementation of electric dipole spin resonance in a macroscopic 3D sample, leveraging spin degrees of freedom to manipulate electric polarization. Finally, I will present the integration of electric fields into an ENDOR-inspired pulse sequence to perform simple quantum algorithms. Our work opens up new possibilities for precise, localized control of spin systems, offering a pathway to more scalable and noise-robust quantum technologies.

Youngwook Park

Affiliation: Fritz Haber Institute of the Max Planck Society

Research Interests: Physical chemistry, molecular physics

Title: Atomic-precision control of photoreactions on surfaces
using laser-coupled STM
Abstract: Scanning probe microscopes (SPMs) have been widely used for monitoring and controlling the local physics and chemistry of materials and molecules at the atomic scale. However, when it comes to photo-induced processes, atomic scale manipulation remains largely unexplored. This is primarily due to the intrinsic discrepancy between optical (μm) and molecular (nm) length scales, which hinders the confinement of photochemistry to the single molecule level. Localized surface plasmons at the SPM junction enable shrinking the photo-excitation to within several tens of nanometers [1]. Using a vanishing gap [2] or employing a pico-cavity [3] has further improved the spatial confinement of the electromagnetic field, driving photoreactions with submolecular precision. We build on these approaches and explore beyond them, especially focusing on systems of chemical importance. We used a low temperature, ultrahigh vacuum scanning tunneling microscope (STM) whose junction is coupled with continuous-wave laser irradiation. Photoreactions are monitored by changes in conductance as well as in tip-enhanced Raman scattering (TERS). In this talk, I will introduce two of our recent endeavors. The first topic concerns a single-molecule photoswitch that operates at a metal–semiconductor junction [4]. A single perylenetetracarboxylic dianhydride (PTCDA) molecule, junctioned between an Ag tip and a Si(111) surface, acts as a conformational switch under laser irradiation, resulting in bistable conductance. The switch involves the reversible breaking and formation of chemical bonds at the molecule–surface interface. Surface plasmons localized at the junction are crucial for triggering the photoreaction The switching behavior is systematically controlled by a 10 picometer-scale vertical motion of the plasmonic tip. The silicon surface, serving as a non- plasmonic counterpart, contributes to this remarkable sensitivity through the formation of strong bonds with the molecule and the inhibition of plasmon generation on the surface. The second part will cover the site-selective photo-dissociation of hydrogen bonds. Triphenylene-2,6,10-tricarboxylic acid (TTC) molecules form two-dimensional honeycomb network structures on an Au(111) surface that are stable at room temperature. In the network, the molecules are hydrogen-bonded via carboxylic groups. In the near-field regime, laser irradiation dissociates the hydrogen bonds, inducing the rearrangement of molecular networks. The photo- induced dissociation of the hydrogen bonds is localized to a few molecules underneath an Ag tip, with minimal impact on neighboring molecules. In contrast, a PtIr tip cannot induce the reaction, suggesting that localized plasmons at the junction contribute to the process. The photoreaction shows a sharp dependence on the wavelength of the incident laser, which is a unique feature of the molecular network.

Pham Thi Hue

Affiliation: University of Ulsan
Research Interests: Condensed matter Physics, Piezoelectricity, Catalytic, Density Functional Theory (DFT), Simulation

Lewis Antill

Affiliation: University of Oxford
Research Interests: Spin Chemistry, Magnetoreception, Photochemistry, Molecular Biology, Microscopy
Title: Developmentof microspectroscopy and simulation software for investigating quantum effectsin biology
Abstract: Flavinsare found throughout nature and participate in a wide range of biochemicalreactions as coenzymes and photoreceptors. Mechanisms involving UV-/blue-lightabsorbing flavoproteins include DNA repair by DNA photolyase and theentrainment of circadian rhythms by cryptochrome, both of which utilise an FADchromophore. Cryptochrome is also central to the chemical magnetoreceptionhypothesis, which operates through spin-correlated radical pairs (SCRPs)generated by a photoinduced electron transfer from a nearby residue to the FADcofactor molecule. The process by which these cryptochrome RPs respond to anexternal magnetic field (MF) is via the radical pair mechanism (RPM), and lowfield effects (LFEs) may allow plants and animals to detect fields as weak asthe geomagnetic field (∼50 μT). I will introduce radical pair theory and discuss ourmicrospectroscopic techniques and software for investigating these (and other)quantum phenomena.

Denis Jankovic

Affiliation: IPCMS (University of Strasbourg/CNRS)
Research Interests: Quantum Physics, Quantum Computing, f-elements, lanthanide complexes
Title: Mathematical modelling of molecular and atomic qudits for efficient gate implementations
Abstract: This presentation bridges the fields of quantum chemistry, atomic physics, and quantum computing by exploring qudits—quantum systems with more than two levels—and their uses in quantum information processing. The benefits of qudits, such as their ability to handle more complex computations with fewer gates, are discussed alongside challenges like increased vulnerability to errors (decoherence) and strategies to overcome them. Key topics include modeling qudits implemented in atomistic or atomistically-adjacent platforms, particularly focusing on the electrically-driven lanthanide hyperfine levels in the Terbium Bisphthalocyanine Single Molecule Magnet, and designing quantum gates using techniques like Givens QR Decomposition and GRAPE. The presentation also touches on cutting-edge methods, such as Physics-Informed Neural Networks, and strategies for optimizing gates to enhance robustness against noise. Whether new to quantum computing or looking to deepen understanding, this presentation aims to provide a comprehensive guide to modeling and optimizing qudit quantum systems.

Mario Ruben

Affiliation: Karlsruher Institut für Technologie (KIT)

Research Interests: Chemistry, Physics

Title: Electrical and Optical Readout and Manipulation of Nuclear Spin States in Molecules

Abstract: Metal complexes will be proposed to acting as active quantum units for Quantum Computing (QC). We report on the implementation of metal complexes into nanometre-sized (single-)molecular spintronic devices by a combination of bottom-up self-assembly and top-down lithography techniques. The controlled generation of magnetic molecular nanostructures on conducting surfaces/electrodes will be shown and persistence of their magnetic properties under confinement in Supramolecular Quantum Devices (SMQD) will be proven. The quantum behaviour (e.g.. superposition, entanglement) of the metal complexes will be addressed at the single molecule level1-13 to finally implement a quantum algorithm on a TbPc2 Qudit performing quantum computing operations.

Masahiro Yamashita

Affiliation: Tohoku University

Research Interests: Coordination Chemistry, Spintronic, Single Molecular Magnet, M-X Chain

Title: Molecular Spin Qubits for Quantum Computer and High – Density Memory Devices Based on Molecular Magnets

Abstract: Spintronics, based on the freedoms of charge and spin of the electron, is a key technology in the 21 st century. Magnetic random access memory (MRAM), which uses giant magnetoresistance (GMR), has several advantages compared with electronics . Although conventional magnets composed of transition metals are normally used, in our study, we use molecule – based nano – magnets and single – molecule magnets (SMMs) to overcome “Moore`s Limitation”. SMMs are also available for quantum computer. I will talk about the molecular spin qubits for quantum computer ([1]Crystal Engineering Method, [2]g – Tensor Engineering Method, [3]Orbital Engineering Method, and [4]Molecular Technology Method) as well as high – density memory devices such as single – molecule memory device, SMMs encapsulated into SWCNT, and metallic cond ucting SMMs with negative magnetoresistances.

Sungkun Hong

Affiliation: University of Stuttgart

Research Interests: Quantum Technology, Quantum Sensing

Title: Quantum levitodynamics: Harnessing quantum motion of levitated particles for fundamental and applied quantum research

Abstract: Quantum levitodynamics is a thriving new field in quantum science that aims to control the quantum motion of micro – and nanoparticles levitated, for example, in optical traps. In recent years, researchers have made rapid progress in achieving quantum control of optically levita ted dielectric nanoparticles. This progress opens up exciting possibilities for the development of new quantum technologies and for testing quantum physics beyond the microscopic world. In this talk, I will give a brief overview of the field and discuss my group’s research activities, in particular our efforts to develop a novel nanophotonic platform for levitodynamics with ultrastrong quantum cooperativity.

Muskan Sande

Affiliation: Sungkyunkwan University

Research Interests: Condensed Matter Physics, Solid State physics, Carbonaceous Nanomaterials, Quantum Physics

Title: Tuning the Magnetic Properties of Two Leg S=1⁄2 Quantum Spin Ladder Ba2CuTeO6 by Chemical Substitution Method

Abstract: The chemical substitution method is widely used for tuning material’s physical and magnetic properties. Tungsten substitution in the Two Leg S=½ Quantum Spin Ladder compound Ba2CuTe1-xWxO6, A2BB′O6 double perovskites, controls the magnetic properties dramatically by suppressing the magnetic ground state. This transition is based on substituting diamagnetic d 10 and d 0 cations into extended superexchange pathways that link magnetic cations. The d10/d0 effect is caused by differences in orbital hybridization in the B–O–B′–O–B superexchange pathways. Our studies investigate the magnetic properties of the two-leg S=½ quantum spin ladder compound Ba2CuTe1-xWxO6 through chemical substitution. By replacing Te 6+ with diamagnetic W6+ cations over a substitution range from x=0.0 to x=0.30, this study aims to understand how these substitutions impact the compound’s magnetic behavior. The substitution of W6+ for Te 6+ introduces significant variations in magnetic exchange interactions, analyzed using magnetic susceptibility, specific heat, Raman scattering, and electron spin resonance (ESR). X-ray diffraction (XRD) pattern and Rietveld analysis show the gradual change in the lattice parameters. The magnetic susceptibility shows a peak at approximately Tmax ~ 70 K, indicating significant spin-singlet correlations. As W content increases, the Curie-Weiss temperature rises, the Néel ordering temperature decreases, enhanced magnetic susceptibility at lower temperatures, and a reduction in spin-ladder correlations. Specific heat measurements display Schottky-like behavior, reflecting localized magnetic excitations and changes in spin-ladder dynamics. Raman scattering studies reveal unconventional magnetic scattering patterns, which change with increasing W content, demonstrating the impact of chemical substitution. ESR data shows a quasi-linear decrease in linewidth with increasing W content, suggesting enhanced quantum critical fluctuations and significant changes in spin dynamics. Our thorough analysis reveals that W substitution drives Ba2CuTe1-xWxO6 closer to a quantum-critical regime, demonstrating the intriguing ability to manipulate magnetic properties in spin-ladder systems.

Johannes Barth

Affiliation: TUM School of Natural Sciences

Research Interests: Molecular Nanoscience & Chemical Physics of Interfaces

Title: Surface-confined metalated graphdiyne sheet

Abstract: Extended organometallic honeycomb alkynyl−silver networks representing metalated graphdiyne sheets have been synthesized on a noble metal surface under ultrahigh vacuum conditions via a gas- mediated surface reaction protocol. Specifically, the controlled exposure to molecular oxygen efficiently deprotonates terminal alkyne moieties of 1,3,5-tris(4-ethynylphenyl)benzene (Ext-TEB) precursors adsorbed on Ag(111), whereby long-range ordered alkynyl−silver networks incorporating substrate atoms are fabricated, featuring Ag-bis-acetylide motifs, high structural quality and a regular arrangement of nanopores with a van der Waals cavity of ≈8.3 nm2 [1]. The electronic features of the adsorbed layer are revealed by complementary scanning tunnelling and angle-resolved photoemission spectroscopies, demonstrating electronic bandstructure formation with an appreciable gap [2]. Extensive density functional theory calculations substantiate the experimental findings in line with recent theoretical insights on the proper combination of frontier molecular orbital and lattice symmetries to generate unconventional band structures. Finally, the transmetalation of the alkynyl-Ag-alkynyl linkages with copper atoms is recognized and implemented as a means to obtain a more robust Ag-GDY sheet with modified electronic properties [3].

Sergey Uchaikin

Affiliation: IBS Center for Axion and Precision Physics Research

Research Interests: Superconductivity, Cryogenic Detectors, SQUID, Axion Search, Quantum Computer
Title: Quantum noise limited amplifier development for Axion Search Experiments at IBS/CAPP
Abstract: Axion search experiments aim to address fundamental questions in physics, including the strong CP problem and the nature of dark matter. The CAPP-MAX experiment at the Center for Axion and Precision Physics Research (CAPP) of the Institute for Basic Science (IBS) in South Korea is a leading effort in this field. This experiment features a 12-T Nb3Sn+NbTi superconducting magnet with a large bore (32 cm), a 37-liter cylindrical copper cavity, and a state-of-the-art microwave readout system utilizing a Josephson Parametric Amplifier (JPA) that approaches the quantum noise limit.

This presentation focuses on the development of a broadband readout system based on superconducting devices, specifically flux-driven Josephson Parametric Amplifiers. Our JPA demonstrates excellent noise performance near the quantum noise limit and has been successfully used in various CAPP experiments operating at 25-50 mK. To enhance the JPA’s bandwidth for wideband scanning experiments like axion searches, we employed techniques to expand its frequency coverage, reducing the need for frequent warm-up and amplifier replacement.

To achieve this, we explored innovative readout design approaches and implemented methods such as combinations of parallel, series, and series-parallel JPA connections. This allowed us to accommodate multiple JPAs within a single readout line. By utilizing multiple JPAs with different operating frequencies, we developed the Dulcimer Amplifier (DA), achieving a readout bandwidth of up to 300 MHz without compromising the JPA’s low noise characteristics. This presentation provides insights into the design considerations and testing methodologies employed for these multi-channel circuits. The outcomes presented here contribute to the advancement of broadband readout systems, offering potential applications in various fields requiring extended bandwidth capabilities.

High School Group Visit

Affiliation: Lycée International Xavier

Talal Mallah

Affiliation: Université Paris-Saclay

Research Interests: Inorganic chemistry, molecular magnetism, quantum information, Prussian blue, spin crossover
Title: Chemical engineering the quantum states of mononuclear Mn(II) and binuclear Cu(II) containing magnetic molecules
Abstract: Spin – based q u antum bits may be considered as competitive qubits because their large coherence times. Among the possible candidates, m agnetic molecules based on transition metal ions or lanthanides (sometimes called molecular (nano)magnets) offer unique advantage because coordination chemistry permits limitless tunability of the quantum states in addition to relativ ely large coherence times. T he association of two (or more molecules) with controlled interaction may allow the design of logic quantum gates. We will disc uss the effect of the axial ligand on the quantum states and on the spin – electric coupling in mononuc lear Mn(II) complexes with trigonal bipyramidal geometry. We also discuss the design of binuclear Cu(II) complexes in the perspective of building tunable quantum gates.

In-Ho Lee

Affiliation: Korea Research Institute of Standards and Science (KRISS)

Research Interests: superfunctional materials design, metasurface design, and artificial intelligence

Title: Designing and exploring super functional materials and devices using deep learning and evolutionary learning methods

Abstract: We introduce a method for designing super functional crystal structures and devices using evolutionary learning and deep learning techniques. Specifically, we present a protocol that combines first – principles electronic structure calculations with global optimization method for super functional cr ystal structure design. Additionally, we describe a data – driven approach for exploring novel crystal structures using generative models. We provide examples of how these methods have been applied to design and explore materials for various applications, in cluding solar cell materials, LED materials, high – mobility materials, topological materials, superconducting materials, and topological – superconducting materials. Finally, we outline a frequency – selective filter design method for 5G communication applicati ons and provide examples of its applications.

Michael Flatté

Affiliation: The University of Iowa

Research Interests: Nanoscience, Spintronics

Title: Proposal to Probe neV to μeV Dynamic Spin Interactions in a Semiconductor with Spin-Polarized DC Scanning Tunneling Spectroscopy

Abstract: A broad range of quantum-coherent spin centers have been identified in optically-accessible materials, especially including nitrogen-vacancy, silicon-vacancy, and germanium-vacancy centers in diamond, divacancies and transition-metal dopants in several polytypes of silicon carbide, and spin centers in 2D materials such as hexagonal boron nitride. Optical probes usually require these spin centers to be well separated, and for integration electrical control and probing would be desirable; long-lived spin centers have also been found in materials that cannot be easily probed optically. Some of the above materials, such as silicon carbide, allow for good electrical transport.

Coherent properties of spin centers in silicon, i.e. dopants, have been probed for many years using “electrically detected magnetic resonance” (EDMR), an electron spin resonance technique that requires an rf field[1]. Recently, however, it has become clear that dc techniques can electrically manipulate and measure the spin orientations of spin centers through the establishment and release of electrical transport bottlenecks[2]. The key requirements of these approaches are a two-dopant or two-site recombination center and a small magnetic field to beat the spin precession against the other timescales of the system. A major advantage is that no ac field of any type is required.

Recently we have proposed that measurements could be made on a single dopant in the transport path (eliminating the two-dopant requirement above) using a spin-polarized electrical contact and a small transverse magnetic field. Some examples of the potential for this approach will be described, including a proposal to measure, at room temperature, the μeV scale exchange and hyperfine fields between spins in a semiconductor using dc magnetoresistance[3], and a proposal to electrically measure zero-field spin splittings and spin coherence times of divacancies in silicon carbide[4].

This work was supported by DOE DE-SC0016447. I acknowledge collaborations with S. R. McMillan, N. Harmon, D. Fehr, J. Sink, and P. M. Lenahan.

Giulia Galli

Affiliation: The University of Chicago

Research Interests: Condensed Matter Physics, Physical Chemistry, Materials Science

Title: Quantum simulations for quantum technologies

Abstract: Which materials are best suited to harness the power of coherent quantum states for quantum applications, including computing, sensing, and communication? Can we predict their physical properties through theory and computation? Can we identify strategies and design rules to synthetize materials with controllable ‘quantum’ noise? I will address these questions for a specific platform for quantum technologies: spin defects in semiconductors and insulators. Electron spins can provide controllable qubits with long relaxation and coherence times, and they can be coupled to nuclear spins for long-lived quantum memories. I will present results of quantum simulations on hybrid quantum-classical architectures for three and two-dimensional solids and illustrate strategies to integrate theory, computation, and experiments.

Andrew Cleland

Affiliation: The University of Chicago

Research Interests: quantum computing, quantum communication, nanomechanics, microfluidics
Title: Quantum control of surface acoustic wave phonons
Abstract: One of the most transformational outcomes promised by research in quantum information is a quantum computer that is exponentially faster than any classical computer. Current state-of-the-art quantum devices have not reached the level of complexity needed to demonstrate this capability, and alternative approaches may enable shortcut routes to achieve this exciting goal. Phonons, representing the collective motion of large numbers of atoms, present an intriguing, completely solid-state approach to quantum information using mobile qubits. Recent developments have shown that phonons can be used as carriers of quantum states, with properties very similar to photons. In this talk I will describe recent results, where we use superconducting qubits for the on-demand generation, storage, and detection of individual microwave-frequency phonons in an acoustic resonator; use phonons to transmit quantum states and generate quantum entanglement; demonstrate a single-phonon interferometer and a quantum information process known as “quantum erasure”; and most recently demonstrate the acoustic Hong-Ou-Mandel effect with phonons, illustrating the wave-particle duality fundamental to quantum mechanics. Interestingly, this last development points to the possible development of a phonon-based architecture for quantum computing.

Christian Schönenberger

Affiliation: Universität Basel

Research Interests: nanoscience, nanoelectronics, quantum physics, quantum electronics
Title: Nanowire-based semi- and superconducting qubits
Abstract: There are a wide variety of physical qubit realizations even in the solid-state alone: transmon, fluxonium, charge, spin, valley, Andreev, and impurity-based qubits. In the quantum- and nanoelectronics group at the University of Basel, we currently work on a range of qubits realized in InAs and GeSi core shell semiconducting nanowires. We have realized Andreev, spin and gatemon qubits. Since time does not permit to address all our results in one lecture, I will focus on two experiments: a) on a singlet-triplet spin qubit based on a double quantum dot realized in a high-quality InAs nanowire, in which zinc-blende and wurzite segments can be controlled with atomic precission; and b) on Andreev qubits realized in InAs nanowires that are coated by a superconducting Al layer in-situ in order to proximitized InAs. For both cases we demonstrate strong coupling to microwave photons in a coplanar transmission line resonator. In case of the Andreev qubits, we could even demonstrate remote qubit-qubit coupling. For this purpose, we have engineered a dedicated coupler circuit that consist of two capacitively linked λ quarter resonators. This system has two distinct modes, a coupler and a readout mode. If both qubits are tuned into resonance to the coupler mode, qubit-qubit operation is possible without loss to the readout line. The challenge for future applications in this platform lies on reaching a large enough parity protection.

Markus Aspelmeyer

Affiliation: University of Vienna

Research Interests: Quantum Optomechanics, Quantum Measurement, Levitated Superconducting Gravimeters, Microscopic Source Masses, Gravitational Quantum Physics
Title: Quantum sources of gravity: the next frontier of macrosopic quantum physics
Abstract: No experiment today provides evidence that gravity requires a quantum description. The growing ability to achieve quantum optical control over massive solid-state objects may change that situation — by enabling experiments that directly probe the phenomenology of quantum states of gravitational source masses. This can lead to experimental outcomes that are inconsistent with the predictions of a purely classical field theory of gravity. Such ‘Quantum Cavendish’ experiments will rely on delocalized motional quantum states of sufficiently massive objects and gravity experiments on the micrometer scale. I review the current status in the lab and the challenges to be overcome for future experiments.
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Joong Il Jake Choi

Affiliation: Center for Nanomaterials and Chemical Reactions, IBS

Research Interests: Surface Science
Title: Lead-Halide Perovskite Surface Degradation: Insights from In Situ Atomic-Scale Analysis
Abstract: While organic-inorganic hybrid perovskites are emerging as promising materials for next-generation photovoltaic applications, the origins and the pathways of the instability of perovskites remain speculative. In particular, the degradation of perovskite surfaces by ambient water is a crucial sub-ject for determining the long-term viability of perovskite-based solar cells. Herein, we employ vari-able-pressure atomic force microscopy (VP-AFM) and near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) to carry out surface characterization and atomic-scale analysis of the reac-tion mechanisms for methylammonium lead bromide (MA(CH3NH3)PbBr3) single-crystal surfaces in environments ranging from ultra-high vacuum (UHV) to ambient pressures. MAPbBr3 single crystals grown in a solution process are mechanically cleaved at UHV to obtain an atomically clean surface. We observe surface inhomogeneity on the freshly cleaved MAPbBr3 surface: the coexist-ence of MA-terminated layers with cubic layer heights, and full and partial coverage of PbBr2-terminated defective layers with lower layer heights. Consecutive topography and friction force measurements in low pressure water (pwater ≈ 10–5 mbar) show the creation of degraded patches that are one atomic layer deep, gradually increasing their coverage until fully covers the surface at water exposure of 4.7 × 104 Langmuir. At the perimeters of these degraded patches, a higher friction coef-ficient was observed, along with an interstitial step height, which we attribute to a structure equiva-lent to that of the MA–Br terminated surface. Combined with NAP-XPS analysis, our results demonstrate that water vapor induces the dissociation of surface methylammonium ligands, eventu-ally resulting in the depletion of the surface MA and the full coverage of hydrocarbon species after exposure to 0.01 mbar of water vapor.

Je-Geun Park

Affiliation: Seoul National University
Research Interests: condensed matter physics, strongly correlated physics, materials science, neutron scattering, magnetism
Title: Van der Waals magnets: a new platform for 2D magnetism
Abstract: Two-dimensional magnetism has played a critical role in the development of modern magnetism, starting from the Heisenberg model proposed in the 1930s. It is not an exaggeration to state that all our modern understanding of matter stands on the theoretical models of Ising, XY, and Heisenberg models, all in two dimensions [1-3]. Despite the massive importance of the three theoretical models, the experimental studies have been slow in coming. There can be several reasons for this unfortunate situation: for example, the lack of adequate experimental tools. However, the primary reason for this lack of experimental studies about true two-dimensional magnetism is the absence of suitable materials. Against this background, the discovery of new two-dimensional magnets in TMPS3 (TM=Mn, Fe, and Ni) in 2016 has been a major breakthrough [4-8]. A dozen new materials have been since added to this growing list of van der Waals magnets, enabling many new experiments that have never been considered. In this talk, I will explain how the field started and developed before sharing several recent research highlights.

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Stefan Tautz

Affiliation: Forschungszentrum Jülich

Research Interests: Quantum Nanoscience

Title: Photoemission orbital tomography: imaging molecular wave functions in reciprocal and real space

Takashi Kumagai

Affiliation: Institute for Molecular Science (Japan)
Research Interests: Scanning probe microscopy, Nanoscale optical spectroscopy, Plasmonics, Single-molecule chemistry, Hydrogen dynamics, Molecular electronics
Title: Nano- & Atomic-Scale Optical Spectroscopy at Surfaces
Abstract: Optical spectroscopy is a powerful tool for chemical analysis, offering a wealth of information on structures, properties, and dynamics of materials. However, the challenge posed by the diffraction limit prevents resolving nanoscale structures directly in optical spectroscopy. This physical limitation can be overcome by near-field optics, capable of controlling electromagnetic fields well below the diffraction limit. In particular, localized surface plasmon resonance of metal nanostructures can lead to strong confinement and enhancement of electromagnetic fields, enabling ultrasensitive optical spectroscopy. Surface- and tip-enhanced spectroscopy, utilizing gap-mode plasmon, has been widely recognized to perform nanoscale and even single-molecule spectroscopy [1-3]. A notable advancement in this area is the integration of tip-enhanced spectroscopy with a low-temperature scanning tunneling microscope, which has achieved sub-molecular resolution in optical spectroscopy [4-7]. This cutting-edge technique not only provides unprecedented insight into light–matter interactions at atomic scales [8] but also will pave the way for Ångström-scale photonics.
Our group aims at developing advanced tip-enhanced spectroscopy to investigate nano- and atomic-scale structures, properties, and light–matter interactions [9-16]. In the talk, I will present our recent results on single atomic-/molecular-level Raman spectroscopy [17, 18], nanoscale coherent spectroscopy [19], and ultrabroadband nanospectroscopy. First, I will discuss Raman scattering of a single atom adsorbed on a metal surface, revealing how atomic-level structures within the plasmonic ‘picocavity’ influence the scattering process. Second, I will discuss anti-Stokes Raman spectroscopy within a single-molecule junction, which demonstrates ‘Joule heating’ of single C60 molecule. Third, I will show nanoscale coherent spectroscopy using 10-fs pulsed laser. This method has enabled us to observe and analyze the ultrafast non-equilibrium dynamics of electron and phonon within the STM junction. Lastly, I will introduce our latest development of ultrafast and ultrabroadband scanning near-field optical microscopy and its application to nanomaterials.

Myungchul Oh

Affiliation: POSTECH (Pohang University of Science and Technology)

Research Interests: Condensed Matter Physics, Quantum Materials

Title: Correlated Phases in Two-dimensional Twisted Moiré Materials

Abstract: In a flat band system, interactions between electrons become dominent due to the suppressed kinetic energy and many-body effect begins to occur. The recent breakthrough in engineering the band structure by creating a moiré superlattice in a twisted two-dimensional system has paved the way for the exploration of numerous strongly correlated quantum phenomena that emerge from the symmetry broken many-body ground state, such as correlated insulators, non-trivial topological phases, and unconventional superconductors [1-4].
In this talk, I will discuss the moiré superlattice flat band engineering in twisted two-dimensional van der Waals heterostructure and the correlated phases in the moiré superlattice systems, and describe underlying many-body physics in those phases.
I will also highlight the novel scanning probe microscopy technique that has enhanced our understanding of the microscopic electronic structures of their ground states [2,4,5].
At the end of this talk, I will discuss on prospects of twisted two-dimensional systems putting recent research progress together.

Jinwon Lee

Affiliation: Delft University of Technology (TU Delft)
Research Interests: Coherent spin dynamics in an atomic scale, Quantum materials, Strongly correlated electron systems
Title: Single-shot readout of the nuclear spin in a single atom using ESR-STM
Abstract: Individual nuclear spins have attracted research interest as promising candidates for the building blocks for quantum memory because they have longer lifetime and coherence time compared to electronic spin states. Most studies on individual nuclear spins have focused on the nuclear spins embedded in solids such as nitrogen-vacancy centers in diamond and single-molecule magnets, which have limited controllability due to their environment. Scanning tunneling microscopy with electron spin resonance (ESR-STM), which allows for precise placement of individual magnetic atoms on a crystal surface, recently observed the nuclear spin state through the hyperfine interaction. However, time-resolved measurements for its relevant timescales have not been reported. In this work, we achieve single-shot measurements of the nuclear spin state of 49Ti atom, which has S=1/2 (electronic) and I=7/2 (nuclear) spins, adsorbed on MgO/Ag(001) using ESR-STM. We apply the pulsed radio-frequency electric field at the fixed frequency, which can drive ESR only when the atom has a certain nuclear spin state and observe whether ESR is driven or not by measuring tunneling conductance. This new approach enables time-resolved measurement of the nuclear spin, and we measure its intrinsic lifetime to be 5 sec, which is 7 orders of magnitude longer than the electronic spin in the same atom. Moreover, we reveal the nuclear spin pumping and relaxation process by sending DC or AC field between the pulses. This long lifetime of the nuclear spin together with the ability of atom manipulation offers a new platform to investigate quantum coherence and entanglement of atomic nuclear spins on surfaces.

Luke Otieno

Affiliation: Kyungpook National University
Research Interests: Microscopy Instrumentation and Control, Nanotechnology, Machine Learning
Title: Scanning a Probe Fast – High-Speed Atomic Force Microscopy
Abstract: Much like the scanning tunnelling microscope (STM) and other scanning probe microscopes (SPMs), the atomic force microscope (AFM) has revolutionized our ability to image and manipulate surfaces at the atomic scale. From unveiling the intricacies of proteins to sculpting nanostructures, its applications span physics, chemistry, biology, and beyond. However, conventional AFMs often face a major bottleneck – slow image acquisition. This significantly limits their throughput and hinders real-time observation of dynamic nanoscale processes. The high-speed AFM (HS-AFM) is the faster cousin of the classic instrument. HS-AFM enables rapid surface characterization and manipulation over larger areas. This opens a new era of possibilities, from characterizing complex biological samples to manipulating surfaces in real-time with unprecedented precision. In this first part of the talk, we will highlight some applications of HS-AFM across various scientific disciplines, dive into the technical advancements that propel the HS-AFM to faster speeds and highlight ongoing challenges and future directions of development.

Christian R. Ast

Affiliation: Max Planck Institute for Solid State Research

Research Interests: STM, ARPES, Superconductivity and Magnetism, Josephson Effect, Dirac Materials

Title: Modeling the Electron Spin Resonance Spectrum in Scanning Tunneling Microscopy

Abstract: The theory of electron spin resonance (ESR) spectroscopy in scanning tunneling microscopy (STM) has been debated for some time now with a number of different proposals having different origin, but essentially leading to very similar results. While the focus so far has been on the ESR signal itself, the measured DC tunneling spectrum offers more details that allow for a more precise verification of the underlying theory. Here, we discuss the ESR signal from a theory point of view by allowing the tunneling electrons to interact with both the driven spin system and the incident microwave during the tunneling process. We find a more complete description of the whole tunneling current also going beyond the typical approximation of a constant density of states.

Magdalena Grzeszczyk

Affiliation: National University of Singapore

Research Interests: Physics

Title: Electrical excitation of carbon centers in hexagonal boron nitride

Abstract: Hexagonal boron nitride (hBN) has emerged as a focal point in diverse research areas, and its significance in optoelectronics has been underscored by the incorporation of carbon. This addition introduces spectroscopic signatures reminiscent of nitrogen-vacancy centers in diamond, maintaining stability even in films characterized by atomic thickness. Notably, this has paved the way for the creation of surface solid-state quantum emitters.

In the seminar, we will explore the systematic developments in creating and characterizing thin layers of carbon-doped hBN, presenting a pathway toward enhanced functionality and possible applications. Utilizing the realm of van der Waals materials, we engineer precise device structures, enabling control over carrier dynamics and defect-related tunneling pathways. Consequently, the carbon centers can be excited electrically in vertical tunnelling junctions. Additionally, the interplay between the Stark effect and the effective dielectric screening allows tunability of their optoelectronic properties.

Kyoung-Whan Kim

Affiliation: Korea Institute of Science and Technology (KIST)

Research Interests: Spintronics, Magnetization dynamics, Spin-orbit coupling

Title: Symmetry manipulation of spin currents in van der Waals heterostructures

Abstract: The generation of a spin current and its role in magnetization dynamics are central topics in spintronics. Over the last decade, there have been intensive studies on the electrical generation of a spin current through charge-to-spin conversion. In spin-orbit coupled materials under an applied electric field, it is known that a transverse spin current can be generated by the spin Hall effect, providing an effective means to manipulate magnetic states. However, the spin Hall effect is subject to symmetry constraints, hindering magnetic switching without an external magnetic field.
In this talk, I will review the symmetry constraints of electrically generated spin current and demonstrate that an effective way to resolve this issue is by exploiting crystalline asymmetry in certain materials, such as WTe2. Unfortunately, the spin-to-charge conversion efficiency in WTe2 is much lower than in conventional transition metals like Pt. Here, we propose a van der Waals heterostructure, WTe2/PtTe2, as an efficient spin source that not only avoids the symmetry constraint but also exhibits a high effective spin Hall conductivity. We introduce a novel spin-to-spin conversion mechanism for the high spin Hall conductivity in the WTe2/PtTe2 multilayer and show that spin-to-spin conversion opens new possibilities in spintronics, which are difficult to be achieved with conventional charge-to-spin conversion mechanism.

Sven Rogge

Affiliation: University of New South Wales

Research Interests: quantum electronics, quantum computation, silicon mesoscopic physics
Title: Erbium sites in silicon with long spin and optical coherence times
Abstract: In solid-state hosts at cryogenic temperatures, rare-earth ions such as Erbium offer low homogeneous broadening and long spin coherence, making them potential assets in optical quantum memories, optical-microwave transducers, and single photon emitters at telecommunication wavelengths. Our study leverages resonant photoluminescence excitation (PLE) spectroscopy to explore spin and optical properties of Er ensembles in silicon, using a setup that combines tailor-made superconducting single photon detectors and fibre optics for high collection efficiency and spectral measurements of samples with low Er density. We discovered that co-dopants like Oxygen, Boron, and Phosphorus have a substantial effect on optically active Er sites and their optical transition energies. Remarkably, we found the first telecom-compatible Er3+ sites in a nuclear-spin-free silicon crystal (<0.01%) with long optical and electron spin coherence times. Both investigated sites showed optical inhomogeneous linewidths around 100 MHz and homogeneous linewidths below 70 kHz. With electron spin coherence times measured via optically detected magnetic resonance and Hahn echo decay constants approximately 1ms at 12 mT, these Er3+ sites in silicon show promise for a multitude of quantum information processing applications.

Yukio Hasegawa

Affiliation: The Institute for Solid State Physics, University of Tokyo

Research Interests: surface science, nanoscale science, scanning tunneling microscopy, superconductivity, STM

Title: Scanning tunnel microscopy on quantum phase transition in atomic layer two-dimensional superconductivity
Abstract: Scanning tunnel microscopy (STM) provides atomically resolved images showing not only the atomic structure of the surfaces, but also their electronic states. Therefore, this technique allows us to observe and evaluate the size effect of vortex formation in nanosized superconductors and the superconducting proximity effect by directly probing the local superconducting gaps and creating images showing their spatial distribution.
In this talk, I present our recent efforts to reveal various unique phenomena that occur in atomically thin two-dimensional (2D) superconductors. 2D superconductors are known to exhibit a superconducting-insulator transition (SIT) at absolute zero temperature by introducing disorder or applying a magnetic field. However, recent studies on atomically thin highly crystalline superconductors have revealed the presence of metallic states intervened between the two phases, which stimulated discussion on the origin of the metallic state and related phenomena on the quantum critical transition. I discuss the possible mechanism of the phase through STM observation of the phase.

Gabriel Aeppli

Affiliation: ETHZ, EPFL, PSI (Switzerland)

Research Interests: Physics, Nanotechnology, Synchrotron

Title: Viable qubits in noisy environments
Abstract: Quantum sensors and qubits are usually two-level systems, quantum analogs of classical bits assuming binary values ‘0′ or ‘1′. They are useful to the extent to which superpositions of ‘0’ and ‘1’ persist despite a noisy environment. The standard prescription to avoid decoherence of solid-state qubits is their isolation via extreme dilution in ultrapure materials. We demonstrate a different strategy using a rare-earth insulator which realizes a dense random network of interacting two-level systems. Qubits with ultralong decoherence times emerge within this network because of rather than in spite of the interactions.

Karl-Heinz Ernst

Affiliation: Empa, Swiss Federal Laboratories for Materials Science and Technology

Research Interests: Surface Science, Chirality, Molecules at Surfaces

Title: Magneto-chiral selectivity, spin-filtering, Kondo physics and topological self-assembly of helicenes on metal surfaces

Abstract: Soon after his seminal discovery of molecular chirality Pasteur suggested physical fields as its origin and assumed that magnetic fields must be the source of chirality in the universe. Lord Kelvin refuted Pasteur’s suggestions and made clear that magnetism has no chirality. In 1894, Pierre Curie proposed that parallel and antiparallel alignments of electric and magnetic fields will induce chirality, but such chiral influence must vanish under conditions of thermodynamic equilibrium. We report that single helical aromatic hydrocarbons, so-called helicenes, undergo enantioselective adsorption on ferromagnetic cobalt surfaces. Spin- and chirality sensitive scanning tunneling microscopy (STM) reveals that molecules of opposite handedness prefer adsorption onto cobalt islands with opposite out-of-plane magnetization. As mobility ceases in the final chemisorbed state, it is concluded that enantioselection must occur in a physisorbed transient precursor state. Such observation suggests electron spin-depend van-der-Waals forces. Simultaneous measurements of the tunneling current through both enantiomers on a given Co nanoisland yields a magneto-chiral specific conductance of up to 50% for single helicene molecules, thus refuting previously proposed ensemble effects as origin of chiralityinduced spin selectivity. Our results open the opportunity towards new single-molecule spinvalve devices and shine light into the origin of the so-called chirality-induced spin selectivity (CISS).

You-Shin No

Affiliation: Konkuk University, Seoul

Research Interests: Low-dimensional optical nanomaterials and nanostructures and nanodevices

Title: On-Demand Hybrid-Integrated Photon Sources
Abstract: Silicon (Si) photonics has been receiving substantial attention as an integration platform in photonics research, owing to the ability to manufacture low-cost, compact integrated circuits. However, realizing efficient and high-quality light sources remain a major challenge. In this talk, I briefly discuss the recent progress of the photonic integration technologies and report on new developments of on-demand, align-transferrable micro-transfer-printing including several micro-manipulation techniques which are useful for addressing key challenges in photonic integration. First, we report on-chip transferrable low-threshold microdisk lasers by utilizing the microstructured polymer-assisted transfer-printing technique. In this work, we designed and fabricated an adhesive PDMS microtip and utilized it to micro-transfer-print single microdisk onto a small Si-post structure [1] and successfully operate rich lasing actions and couple the laser emission to a Si waveguide. Second, we also report on an all-graphene-contact approach to introduce the transparent and flexible electrical contacts to a vertically p-i-n doped active semiconductor nanostructure and to operate it by pulsed current injection [2,3]. Finally, we report on a recent result of an on-demand minimal gain-printed continuous-wave nanolaser-on-silicon at room temperature. The method and techniques in this talk can be very useful to facilitate light source integration in Si photonics and further help to realize high-density ultracompact photonic integrated circuits.

Uwe R. Fischer

Affiliation: Seoul National University

Research Interests: ultracold quantum gasesmany-body physics, analogue gravity, quantum metrology, quantum simulation

Title: Quantum Simulation, Quantum Metrology and Quantum Engineering at SNU

Abstract: After a general introduction into the research activities of my Theory of Cold Atoms group at Seoul National University comprising, inter alia, fields as mentioned in the title, I will focus more specifically on the ramifications of the genuine quantum resources entanglement and steering onto two rather diverse phenomena: The analogue of cosmological particle creation in the early Universe (quantum simulation) and the usage of entanglement to enhance the charging power of quantum batteries (quantum engineering).

Lucas Schneider

Affiliation: University of California, Berkeley

Research Interests: Scanning Tunneling Microscopy, Superconductivity, Topology in Condensed Matter Physics, 2D Materials

Title: Superconductivity in atom-by-atom crafted quantum corrals

Abstract: Gapless materials in electronic contact with superconductors acquire proximity-induced superconductivity in a region near the interface. Here, we investigate the most miniature example of this so-called proximity effect on only a single quantum level of a surface state confined in a quantum corral on a superconducting substrate, built atom-by-atom using a scanning tunneling microscope. Whenever an eigenmode of the corral is pitched close to the Fermi energy by adjusting the corral’s size, a pair of very sharp particle-hole symmetric states is found to enter the superconductor’s gap. By comparison to a resonant level model of a spin-degenerate localized state coupled to a superconducting bath, we identify the in-gap states as scattering resonances theoretically predicted in 1972 which had so far eluded detection [1]. We further show that the observed anticrossings of the in-gap states indicate proximity-induced pairing in the quantum corral’s eigenmodes [2]. Based on these insights, I will discuss the implications on induced superconductivity in the surface state of noble metal Ag(111) grown on superconducting Nb(110). Notably, we find that the lifetime of electronic states is strongly enhanced by the presence of a proximity-induced bulk gap. Finally, we study how magnetic adatoms interact with the corral’s eigenmodes. Understanding their coupling eventually allows us to tailor a mirage effect [3] of Yu-Shiba-Rusinov sub-gap states induced by Fe atoms [4].

Chi Chen

Affiliation: Academia Sinica, Taiwan

Research Interests: SNOM, TERS, AFM, Spectroscopy of Single molecules and nanomaterials

Title: 
Combing Photon with SPM for STM-EL, TERS, and SNOM

Abstract: Combing optics with scanning probe microscopy (SPM) enables new possibilities of cutting – edge discoveries , such as tunneling induced electroluminescence (STM – EL), tip – enhanced Raman or photoluminescence spectroscopy (TERS/TEPL), and aperture or scattering scanning near – field optical microscopy (a – /s – SNOM). In this talk, I first introduce the basic principle of confocal optics and the light path design for tip illumination/photon collection. The instrumentation of both STM – optics and A FM – optics will be presented and compared. Three different categories of experiments are included: (1) STM – EL from single molecules and atomic chains at cryogenic temperatures and UHV environments. (2) STM – TERS of carbon nanotubes under ambient conditions. (3) AFM – SNOM of 2D materials in ambient conditions and AFM – SNOM of lipid bilayers in liquid.

Rudolf Haindl

Affiliation: Max Planck Institute for Multidisciplinary Sciences and Georg August University of Göttingen (Germany)

Research Interests: Physics, Electron Microscopy

Title: Coulomb-correlated few-electron states in a transmission electron microscope beam

Abstract: Correlations between electrons are at the core of numerous phenomena in atomic, molecular, and solid-state systems. However, harnessing free-particle correlations remains challenging, with the recent implementation of nanoscale single-electron sources [1] and observation of anti-bunching in electron beams [2, 3, 4]. A powerful approach to induce strong inter-electron interactions is femtosecond-triggered photoemission from nanotips [5,6] with high spatial and temporal confinement. However, ensemble-averaged detection typically conceals few-body effects. In this work, we characterize Coulomb correlations in laser-triggered electron number states generated at a Schottky field emitter in an ultrafast transmission electron microscope [7]. Based on an event-based detection scheme, we separate the state-averaged spectrum into the n-state components with a characteristic n-peak spectral shape. Furthermore, we identify a characteristic pair-correlation energy of around 2 eV. The strong inter-particle energy exchange is caused by acceleration-enhanced inter-particle Coulomb interaction, as confirmed by trajectory simulations. State-sorted beam caustics reveal a discrete increase in virtual source size, a longitudinal source shift, and a pronounced angular distribution of the few-electron states compared to single-electron pulses. The high fidelity of few-electron pulses in conjunction with single-particle detection enables the application of various experimental schemes typically employed in quantum optics. Specifically, we propose a scheme to generate an electron beam with sub- and super-Poissonian two-electron statistics. Applications of such beams include heralded single-electron sources and may foster new developments in free-electron quantum optics and quantum-enhanced electron microscopy.

John H. Gaida

Affiliation: Max Planck Institute for Multidisciplinary Sciences and Georg August University of Göttingen (Germany)

Research interests: Physics

Title: Attosecond electron microscopy using Lorentz PINEM and free-electron homodyne detection

Abstract:  Transmission electron microscopy (TEM) offers high spatial resolution and is widely used to characterize optical ex citations and near fields by electron energy loss spectroscopy (EELS). This method probes self – induced electric fields in the nanostructure, using spontaneous inelastic scattering of electrons. Importantly, it is difficult to experimentally access near – fie ld phase information. Using external laser excitation, strong optical near fields can induce stimulated inelastic electron – light scattering, as employed in photon – induced near – field electron microscopy (PINEM). In this case, optical modes populated at the laser frequency are excited, providing enhanced spectral resolution and polarization sensitivity. Importantly, in this process, the induced near field is phase – locked to the exciting laser, which translates to a coherent phase modulation of the electron wa ve function. In this talk , we present two phase contrast techniques for imaging optical near fields at nanostructures. Specifically, we implement Lorentz – mode PINEM and free – electron homodyne detection (FREHD). Using these techniques, we image optical fields with subwave length (10 nm) spatial and sub – cycle temporal resolutions. Lorentz microscopy is an in – line holography technique, employing Fresnel diffraction at a small defocus. The electron wave function is locally mixed, and contrast arises near phase gradients. Sensitivity to the light field is obtained by energy filtering T EM (EFTEM) of PINEM – induced sidebands in the electron spectrum. We obtain complementary information about the phase profile by exploiting the conjugate symmetry of the energy gain and loss sidebands. From two complementary measurements, we reconstruct the light – imprinted phase using an iterative reconstruction algorithm. In the newly developed FREHD technique, on the other hand, we measure the phase profile by means of a phase – controlled reference interaction. The near field at a sample modulates the phase of the electron wavefunction. This wavefunction modulation is amplified or attenuated for in – phase and anti – phase reference interactions, respectively, which allows for a coherent read – out of a position – dependent phase. Overall, FREHD transfers concepts from homodyne detection in optics and amplitude (AM) and frequency modulation (FM) in radio techno logy to the realm of electron microscopy. Combining free electrons with phase – locked laser excitation offers fascinating new possibilities to image local attosecond and phase – resolved responses on the nanometer scale.

Giorgio Sangiovanni

Affiliation: Julius-Maximilians-Universität Würzburg
Research Interests: condensed matter theory
Title: Real-space Obstruction in Quantum Spin Hall Insulators
Abstract: In the hunt for room-temperature quantum spin Hall insulators, bismuthene [1] has demonstrated the impressive advantage of a local spin-orbit coupling experienced by the in-plane p-orbitals. This alternative to pi-bond graphene can be pushed to a conceptually even more essential level upon halving the honeycomb lattice, i.e. considering chiral p-orbitals on a triangular lattice [2]. Here, we theoretically conceive and experimentally realize for the first time a triangular QSHI, indenene, an indium monolayer exhibiting non-trivial valley physics and a large gap. We identify an interference mechanism of the Bloch functions and the emergence of a hidden honeycomb pattern in the charge localization, which makes the topological classification accessible to bulk experiments, without the necessity of quantum edge transport.

Alessandro Toschi

Affiliation: Institute of Solid State Physics (Technische Universität Wien)
Research Interests: Theoretical Physics, Electronic Correlations, Superconductivity, Quantum Criticality
Title: Local Moment Formation and Kondo screening from the Charge-Sector Perspective: How Perturbation Theory breaks down
Abstract: In this talk, I will discuss how the correct physical description of the formation of local moments and of their Kondo screening gets reflected in the charge-scattering sector. In particular, by a systematic analysis of the on-site charge and spin fluctuations on Hubbard atom, Anderson Impurity Model and Hubbard model solved by means of dynamical mean-field theory, I will demonstrate [1] how the strong intertwining between the different (spin and charge) sectors, which is crucial for a coherent description of correlated metallic and Mott insulating phases, necessarily drives the breakdown of the self-consistent perturbation expansion [1,2].
The improved understanding of the frequency structures of the two-particle correlation functions has also allowed us [2] to identify the typical fingerprints of the Kondo physics in the charge sector and, on an even more quantitative level, to introduce a new, quite accurate criterion for estimating the Kondo temperature. Interestingly, the same scattering processes responsible for the on-site charge localization may result in an effective electronic attraction [3,4], triggering the phase-separation instabilities emerging in the proximity of Mott-Hubbard or Hund’s-Mott metal-insulator transitions.

Pascal Ruffieux

Affiliation: Swiss Federal Laboratories for Materials Science and Technology

Research Interests: nanographene, graphene nanoribbon, surface science
Title: On-surface synthesis of magnetic nanographenes
Abstract: Recent progress in the on-surface synthesis of nanographenes has given access to an extremely rich materials class where physical properties can be tuned in a wide range. The most prominent nanographenes include armchair graphene nanoribbons (GNRs) with width-dependent electronic band gaps [1], zigzag GNRs with spin-polarized edge states [2] and width-modulated GNRs hosting tunable topological bands [3]. Most recently, the successful synthesis of a series of open-shell nanographenes with magnetically nontrivial ground states has catapulted carbon-based magnetism to a new level. The basic concept followed here is realization of sublattice-imbalanced or topologically frustrated nanographenes hosting unpaired electrons. A deterministic realization of such nanographenes is achieved through a combined solution on and on-surface synthesis approach. Here, I will report recent advances in the on-surfaces synthesis of nanographenes with chemically tuned magnetic interaction strength between unpaired electrons in diradical nanographenes [4]. The controlled combination of different magnetic nanographenes allows formation of both, antiferromagnetically and ferromagnetically coupled dimers and trimers based on spin-½ and spin-1 molecular building blocks as well as extended spin chains [5]. Here, we investigate the length and site-dependent spin excitations with inelastic scanning tunneling spectroscopy and compare them theoretical predictions on spin-1 chains and confirm Haldane gap and fractional edge excitations for open chains. As an extension of the on-surface synthesis approach, we recently achieved successful formation of open-shell nanographenes using scanning tunneling microscopy tip-based activation of hydrogen-protected precursors [6,7]. This has the advantage that magnetic nanographenes can be prepared and characterized on a larger range of substrates since no specific catalytic substrate properties are needed here.

Andreas Osterwalder

Affiliation: Ecole Polytechnique Federale de Lausanne (EPFL)

Research Interests: Physics

Title: From cold gas-phase stereodynamics to kinetics at water-water interfaces

Abstract: I will briefly introduce the two primary research directions covered in our group:
A first part will be on experiments to study sub-Kelvin stereodynamics in merged beams. We investigate prototypical energy transfer reactions in the gas phase, namely between metastable Ne(3P2) and other rare gas atoms or small molecules. Such reactions can proceed along two pathways according to       NeX+ + e ̄← Ne(3P2) + X → Ne(1S) +X+ + e ̄       called Penning ionization (producing X+) and associative ionization (producing NeX+), respectively. At high energies the branching ratio between these channels can be controlled through the orientation of the Ne(3P2) atom, but this ability is lost at low energies due to a reorientation of the reactants. In the second part I will be describing our efforts towards studies of gas — liquid water scattering dynamics, for which we cross a molecular beam with a liquid water flat-jet. Liquid flat-jets can be produced by impinging two cylindrical microjets at controlled angles and flow-rates. Such an arrangement produces a series of drop-shaped leaves that provide a flat surface from which gas-phase molecules can be scattered. But, as will be shown, the first leaf in this chain can also serve as a tool to prepare a controlled interface between two liquids, possible miscible, an arrangement that is ideally suited for the study of chemical kinetics at liquid-liquid interfaces.

Claudiu Genes

Academic Affiliation: Max Planck Institute for the Science of Light

Research Interests: Quantum optics, Molecular quantum technologies, Quantum information, Quantum sensing, Organic opto-electronics, Cooperative quantum phenomena, Quantum metrology, Quantum optomechanics, Energy and charge transport

Title: Quantum optics with molecules

Abstract: Theoretical tools of quantum optics, such as the master equation and the quantum Langevin equations approaches, are ideally suited to treat the dynamics of complex open quantum systems. A reduction to basic ingredients has seen such methods successfully applied to ensembles of two level quantum emitters, where the electronic degree of freedom is interfaced with single or multimode quantum light. Standard aspects tackled within this formalism include free space cooperative effects such as super – and subradiance (radiative emission rates larger or smaller than that of an isolated individual system) and cavity quantum electrodynamics effects such as strong coupling, polariton physics or Purcell enhancement of spontaneous emission rates.

Duck-Ho Kim

Affiliation: Korea Institute of Science and Technology (KIST)

Research interests: Spintronics

Title: Spin Transport and Dynamics in Ferrimagnetic Materials

Abstract: The dynamic phenomena of topological spin objects in magnetic materials have been actively studied not only for their academic interest but also for their potential applications in next – generation memory devices [1 – 4]. Representative topological spin objec ts include chiral magnetic domain walls [1, 2] and magnetic skyrmions [3, 4]. It is possible to manipulate topological spin objects using electric current, and the underlying mechanism involves the conservation of angular momentum arising from the interact ion between the electron’s spin and the spin of the phase spin structure as the electron traverses the magnetic material [5, 6]. This interaction is known as spin torque and can be divided into spin – transfer torque and spin – orbit torque depending on the tr ansmitting materials . Recently, ultrafast motion of topological spin objects has been predicted in antiferromagnetic materials (total magnetization = 0) through theoretical studies [7]. Unfortunately, antiferromagnetic materials are difficult to measure (t otal magnetization = 0) and challenging to control (due to strong coupling energy), making it difficult to experimentally verify the theory. However, in the case of ferrimagnetic materials, which have a finite magnetization at the angular momentum compensa tion point where the angular momentum is zero, it has been possible to investigate the spin dynamics of antiferromagnetic materials. With this possibility, ultrafast motion has been observed at the angular momentum compensation point when topological spin objects are driven by a magnetic field [8]. In this presentation, we will discuss the spin transfer torque phenomenon [9] and the phenomenon of skyrmion hall effect [10] at the angular momentum compensation point when topological spin structures is driven by electric current in ferrimagnetic materials

Woo-Joong Kim

Affiliation: Professor of Physics, Seattle University

Research interests: Precision force measurements, Casimir and van der Waals forces, surface patch effect, quantum conductance in nanowire
Title: An optically-driven macroscopic cantilever
Abstract: I will report an interferometric experiment to detect optically-driven resonance on a macroscopic object. Utilizing dynamic force microscopy, the resonant motion of a cm-sized cantilever driven by an amplitude-modulated laser is directly observed. I will also discuss other experimental techniques underway in our research lab and their potential applications to precision measurements such as tests of short-range gravity.

Sungkyun Choi

Affiliation: Center for Integrated Nanostructure Physics IBS, SungKyunKwan University

Research interests: Quantum Spin Liquids, Multiferroics, Topology in Magnetism, Quantum Phase Transitions
Title: Spectroscopy on Quantum Magnetism
Abstract: In this seminar, we will introduce how spectroscopy can be utilized in understanding contemporary research topics in condensed matter physics, in which quantum magnetism plays an important role. To this end, our primary experimental technique is neutron spectroscopy, complemented by X – ray and Raman spectroscopy. Case examples such as quantum spin liquids, multiferroics, and insulator – metal transitions will be discussed.

Pierre Josse

Affiliation: University of Angers, Yonsei University

Research interests: Organic Chemistry, Dye Chemistry, Organic Electronics
Title: Tailoring π-conjugated molecular and macromolecular systems for addressing specific needs and requirements: from organic photovoltaics to theranostics
Abstract: Active materials for organic electronic applications such as solar cells or light emitting diodes usually requires strong absorbers and/or emitters in the visible/NIR range. Over the last 30 years, researchers around the world have been developing new materials, optimizing devices and rationalizing structures/properties relationships to demonstrate the interest of these technologies and potentially bring them on the market. The rapid growth of organic electronics was then closely related to the capacity of synthetic chemists to generate new and original molecular and macromolecular structures . With the only limitation being basically the imagination, organic synthesis indeed offers countless reactivities, tools and possibilities to afford functional compounds with specific properties. As a chemist specialized in π-conjugated systems, I’ll thus cover, through this presentation, projects and strategies developed to address specific needs and requirements for practical applications ranging from organic photovoltaics to light emitting devices and even photosensitizers for theranostic applications.

Vasily Kravtsov

Affiliation: ITMO University

Research interests: Two-dimensional quantum materials, ultrafast spectroscopy, nonlinear nano-optics
Title: Near-field spectroscopy and control of excitons in 2D van der Waals heterostructures.
Abstract: Atomically thin transition metal dichalcogenides (TMDs) are direct band gap semiconductors that host excitons with large binding energies and sizeable exciton – exciton interaction strength. When stacked into heterostructures, these materials acquire many unique optical properties associated with the interlayer coupling and formation of new excitonic and polaritonic states. Near – field spectroscopy provides an indispensable tool for studying such states, as well as their coupling, dynamics, and control. I w ill present results of our recent investigation of excitonic effects in van der Waals heterostructures via different near – field spectroscopy implementations including tip – enhanced spectroscopy and spectroscopy in the Fourier plane via evanescent wave coupling through a solid immersion lens. First, I will discuss the possibility of controlling the intralayer and interlayer excitons within a nanoscopic volume of TMD heterobilayers. Second, I will discuss experiments on probing and controlling exciton – polarito ns in all van-der-Waals heterostacks in the strong light-matter coupling regime.

Paul Weiss

Academic Affiliation: University of California, Los Angeles (UCLA)

Research interests: Nanoscience, Chemistry, Physics, Nanotechnology, Biotechnology

Title: Understanding and Controlling Charge, Heat, and Spin at Atomically Precise Interfaces

Abstract: One of the key advances in nanoscience and nanotechnology has been our increasing ability to reach the limits of atomically precise structures. By having developed the “eyes” to see, to record spectra, and to measure function at the nanoscale, we have been able to fabricate structures with precision as well as to understand the important and intrinsic heterogeneity of function found in these assemblies. The physical, electronic, mechanical, and chemical connections that materials make to one another and to the outside world are critical. Just as the properties and applications of conventional semiconductor devices
depend on these contacts, so do nanomaterials, many nanoscale measurements, and devices of the future. We explore the important roles that these contacts can play in preserving key transport and other properties. Initial nanoscale connections and measurements guide the path to future opportunities and challenges ahead. Band alignment, minimally disruptive connections, and control of spin and heat are all targets and can be characterized in both experiment and theory. I discuss our initial forays into this area in a number of materials systems.

Ruslan Temirov

Academic Affiliation: Peter Grunberg Institute, Forschungszentrum Jülich

Research interests: Scanning Probe Microscopy, Cryogenics

Kyoung-Duck Park

Academic Affiliation: Pohang University of Science and Technology (POSTECH)
Research interests: Physics
Title: Tip-enhanced cavity-spectroscopy

Maria Spethmann

Affiliation: University of Basel

Title: High-fidelity two-qubit gates of hybrid superconducting-semiconducting singlet-triplet qubits

Abstract:

Hybrid systems comprising superconducting and semiconducting materials are promising architectures for quantum computing. Superconductors induce interactions between the spin degrees of freedom of semiconducting quantum dots, based on crossed Andreev processes. In the talk I will present our theory where we show that these interactions are widely anisotropic when the semiconductor material has strong spin-orbit interactions. This anisotropy is tunable and enables fast and high-fidelity two-qubit gates between singlet-triplet spin qubits. The reason is that the design is immune to leakage into non-computational states and removes always-on  interactions between the qubits (crosstalk). We estimate two-qubit gate fidelities exceeding 99.9% without fine-tuning of parameters.

Daniel Kyungdeock Park

Academic Affiliation: Yonsei University

Title: Quantum machine learning: opportunities and challenges

Abstract:

Quantum computing has the potential to outperform any foreseeable classical computers for solving certain computational problems. With the growing demand for advanced computing power and methods in big data and artificial intelligence, quantum machine learning (QML) has emerged as one of the most exciting applications of quantum computing. In its early developments, QML gathered much attention mainly due to the quantum algorithm that solves the system of linear equations exponentially faster than its classical counterpart. However, this algorithm requires a fault-tolerant quantum computer and a quantum random access memory, which remain long-term prospect. Thus an important and challenging question is how noisy intermediate-scale quantum (NISQ) computers that are within reach can be utilized for QML. In this talk, I will first briefly introduce quantum machine learning. Then I will present several QML approaches that aim to utilize NISQ to the full extent and attain quantum advantages in the near future.

Joseph A Stroscio

Title: Unraveling Quantum Geometry and Orbital Magnetism Contributions to Landau Levels in Moiré Superlattices

Abstract:

Flat and narrow band physics in moiré quantum matter (MQM) has proven to be extremely rich with new emergent quantum phases which can be tuned with applied electric and magnetic fields. The topological properties of the eigenstates of the moiré Hamiltonian are critical for establishing the quantum phase of the system. While the emergence of non-trivial Chern numbers has been observed, it is important to characterize the quantum geometry in detail including the Berry curvature and the less known quantum metric effects which give rise to orbital magnetism in these systems. For almost a century, magnetic oscillations have been a powerful “quantum ruler” for measuring Fermi surface topology. In this presentation, I show the use of a quantum ruler of Landau levels via scanning tunneling spectroscopy to probe quantum geometry and topology in twisted double bilayer graphene (TDBG) [1]. The high-resolution Landau level spectra reveal tunable electron- and hole-like pockets that deviate significantly in their magnetic response from the semiclassical Onsager relation. A quantitative analysis of the Landau levels demonstrates the significance of quantum geometry contributions to the magnetic energy levels, highlighting the effect of the tunable Berry curvature and local orbital magnetism. The deviation from semiclassical behavior is due to the higher order magnetic field response of TDBG, which in turn is related to the quantum geometry of the electronic structure. The first-order correction in magnetic field, interpreted as an orbital magnetic moment, manifests as a valley splitting of the Landau levels. The second-order correction—orbital magnetic suscepti

Clément Cabanetos

Academic Affiliation: University of Angers

Title: “Sooner or later, everything old is new again”: Functionalization and use of a forgotten dye

Abstract:

Abstract: Since the advent of organic electronics, various classes of π-conjugated molecular and macromolecular semiconductors have been reported. Among them, imide-containing rylenes have attracted considerable research attention due to their redox, electron-withdrawing and charge-carrier transport properties, as well as their excellent chemical, thermal, and photochemical stabilities. Naphthalene diimide (NDI) and perylene diimide (PDI) can be unequivocally recognized as the most studied imide based building blocks for the preparation of high-performance electron transporting optoelectronic materials. Within these wide-ranging studies, considerable effort has been undertaken to functionalize both the bay positions and the nitrogen atom constituting the imide group (N-positions) to bring solubility, tune the molecular (opto)electronic characteristics, and build extended π-conjugated architectures. Despite interesting fluorescent properties, the N-(alkyl)benzothioxanthene-3,4-dicarboximide (BTI), a sulfur containing rylene-imide dye, has not yet triggered such interest. Exclusively functionalized on the N-position for imaging and staining applications, we recently focused our attention in functionalizing the p-conjugated core of this forgotten dye for the preparation of new and original materials for organic electronics, but not only… 

Clément Cabanetos: clement.cabanetos@cnrs.fr

 After graduation in 2008, Clément Cabanetos undertook a PhD at the CEISAM laboratory (Nantes, France) on the synthesis of new crosslinkable polymers for nonlinear optical applications. Shortly after his thesis defense, he joined the group of Jean Fréchet (KAUST, (Saudi Arabia) as a postdoctoral fellow to prepare efficient π-conjugated macromolecular materials for organic photovoltaics. In 2013, he was recruited as a permanent CNRS researcher and joined the MOLTECH-Anjou laboratory in Angers to develop new and original concepts for organic electronics. He then defended his habilitation in 2018 (associate professorship) and received in 2019 the CNRS bronze medal that awards young and promising researchers. Recently (august 2021) he moved to Seoul in a joint French (CNRS)-Korean International laboratory (2BFUEL) hosted by the Yonsei University where he was promoted director in September 2022.

Pavel Jelinek

Academic Affiliation: Institute of Physics of the Czech Academy of Sciences (FZU)

Title: Quinone-based 1D molecular chains on surfaces: magnetism and nuclear quantum effects

Abstract:

Low dimensional materials offer very interesting material and physical properties due to reduced dimensionality. At present, 2D materials are the focus of attention. However, 1D systems often show far more exotic behavior due to reduced dimensionality enhancing substantially quasiparticle interactions. However, synthesis of purely 1D molecular systems still remains elusive. In this talk, we will explore on-surface chemistry using 2,5-diamino-1,4-benzoquinonediimines (2HQDI) precursor [1], which offers interesting playground for growing molecular chains of distinct chemical character.

In first part of the talk, we will present formation of hydrogen-bonded 2HQDI molecular chains on Au(111) surface. We will discuss a significant influence of nuclear quantum effects on structural, mechanical and electronic properties of these 2HQDI molecular chains. Namely, we demonstrate that the presence of concerted proton motion not only enhances significantly the cohesive energy of intermolecular hydrogen bonds but it also causes emergence of new electronic states located at the edges [2].

In the second part, we introduce on-surface synthesis of 1D coordination p-d conjugated polymers, achieved by co-deposition of 2HQDI molecular precursor and various transition metals (Fe, Co, Ni, Cr, Cu) atoms on metal surfaces under UHV conditions [3]. This route results in formation of flexible coordination polymers with length up to hundreds of nanometers. We characterize physical and chemical properties by means of low temperature UHV scanning probe microscopy supported by theoretical simulations. We will discuss distinct coordination of transition metal and corresponding atomic, electronic and magnetic structure [4]

Finally, we will demonstrate fully reversible multiconfigurational light-driven spin crossover switches in a single p-d organometallic Co-QDI chain suspended between two electrodes.  The external light enables us to realize reversible spin cross over between low and high-spin states of individual cobalt centers within the chain.

[1] O. Siri, et al  J. Am. Chem. Soc. 125, 13793 (2003).

[2] A. Cahlik et al ACS Nano 15, 10357 (2021).

[3] V.M. Santhini et al, Angew. Chem. Int. Ed. 60, 439 (2021).

[4] Ch. Wackerlin et al, ACS Nano (2022) DOI: 10.1021/acsnano.2c05609

Wolf-Dieter Schneider

Academic Affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL)

Title: A short history of spectroscopic manifestations of the Kondo effect

Han-woong Yeom

Academic Affiliation: CALDES, IBS & POSTECH

Title: Nano-tsunami along atomic chains and domain walls for robust informatics

Abstract:

Storing and manipulating information in robust and dissipationless ways is of prime interest in various fields of science and technology. Using topologically protected local excitations, form examples, skyrmions and Majorana fermions, such robust informatics may be realized. This talk reviews our own approach to this issue, which deals with new types of solitons in electronic systems. We will first discuss atomic chains formed on silicon surfaces in charge-density-wave ground states and their solitons. We recently identified individual electronic solitons in indium atomic chains on a Si(111) surface and, more recently, in silicon chains on stepped silicon surfaces . Due to their unique structures, they represent unprecedented topological systems of Z₄ [1] and Z₃ [2], respectively, with three and two distinct solitons. These solitons can store, deliver, and operate multi-level information bits, which are protected topologically [3]. We further demonstrate solitons with higher multiplicity can be formed as a form of mobile kinks [4] along the charge-density-wave domain walls on a 2D material of 1T-TaS₂ [5]. Thus, the possibility of multi-level and topologically protected information processing with solitons, or solitonics, is well demonstrated. Further studies on soliton-defect, soliton-soliton, and soliton-excitation interactions are exciting for soliton applications.

References:

[1] S. M. Cheon, S. H. Lee, T. H. Kim, and H. W. Yeom, Science 350, 182 (2015).

[2] J. W. Park, E. Do, J. S. Shin, S. K. Song, O. P. Jelinek, and H. W. Yeom, Nature Nanotechnology 17, 244 (2022).

[3] S. M. Cheon, T. H. Kim, and H. W. Yeom, Nature Physics 13, 444 (2017).

[4] J. W. Lee, J. W. Park, and H. W. Yeom, PRL, under review (2022).

[5] D. Cho, G. Gye, J. Lee, S. H. Lee, L. Wnag, S-W. Cheong, and H. W. Yeom, Nature Commun. 8, 392 (2017)

Han Woong Yeom^1,2

¹Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang 37673, Korea.

²Department of Physics, POSTECH, Pohang 37673, Korea.

Harald Brune

Academic Affiliation: Ecole Polytechnique Fédérale de Lausanne (EPFL)

Title: The role of External Shells in the Magnetic Stability of Single Rare-Earth Adatoms, new SAMs,  and Graphene Transfer under UHV

Abstract:

An important and often neglected fact in the magnetic stability of single rare-earth adatoms is the spin-polarization of their outer shells. It stems from charge transfer to the surface [1] and gives rise to an additional magnetic moment that is strongly coupled to the large and well-screened moment of the 4f electrons [2]. We present experimental evidence for Dy/g/Ir(111) that the total angular momentum resulting from these coupled 4f 5d6s moments is in fact the good quantum number that decides which states are stable and which mechanisms for reversal exist in a given crystal field [3]. Recent theoretical works have pointed out the importance of valence 5d6s shells for single atom and single ion molecular magnets [4], however, direct experimental evidence for the importance of these shells in the spin dynamics was so far lacking.

We discuss the most recent single atom magnets (SAMs) with focus on two cases where the easy axis is lying in-plane. The first is Dy on the TiO2(100)-terminated Dy/SrTiO3(100) surface [5] and the second Dy on MgO bridge sites [6]. In the first case, we present XMCD results and in the second preliminary SP-STM results studying the two-state switching as function of tunnel bias that we discuss in the context of published XMCD data [7]. In order to cap, respectively, seal samples that are sensitive to oxidation and other chemical reactions in ambient, we have transferred graphene under ultra-high vacuum. Since this is potentially relevant also for single atom magnets, we present our results that show clean graphene transfer under UHV onto Cu(100) and Ir(111) target samples using a wafer bonding approach.

[1] M. Pivetta et al. PRB 98, 115417 (2018).
[2] M. Pivetta et al. PRX 10, 031054 (2020).
[3] A. Curcella et al. to be published (2022).
[4] V. Dubrovin et al. Chem. Communic. 55, 13963 (2019) & Inorg. Chem. Front. 8, 2373 (2021).
[5] V. Bellini et al. ACS Nano 16, 11182 (2021).
[6] C. Soulard et al. in preparation (2022).
[7] F. Donati et al. Nano Lett. 21, 8266 (2021).
[8] D. Merk et al. submitted (2022).

Jingcheng Li

Academic Affiliation: Sun Yat-sen University

Title: Inducing magnetic properties in graphene nanostructures

Abstract:

Spin in carbon-based materials shows long coherence time, tunable coupling strength, and can be incorporated into scalable carbon platform, which makes it promising for quantum computing and spintronics applications.  Predictions state that graphene structures with specific edge topology can spontaneously develop magnetism, but the difficulty in their synthesis and magnetism characterization hinders the experimental verification. Here in this talk, I will show you our latest results on the observation and manipulation of magnetic moments in such graphene open-shell nanostructures. The graphene open-shell nanostructures with different edge topology, size and doping are created on a gold surface through on-surface synthesis route with atomic precision. Using scanning tunneling spectroscopy, we can detect the presence of electron spins and map their localization. With the experimental results and theoretical simulations, I will demonstrate that how the electronic correlations, πbond frustration or topological band engineering can be used to induce spin states in graphene nanostructures.

Yousoo Kim

Academic Affiliation: University of Tokyo

Title: Single-molecule spectroscopy using localized-surface plasmon

Abstract:

Irradiation of light to the metallic nanostructure causes collective vibration of free electrons (plasmon), followed by the creation of an electromagnetic field, i.e., localized surface plasmon (LSP). The LSP has a characteristic interaction with matter, especially a single molecule. The scanning tunneling microscope (STM) is a versatile and powerful tool for investigating and controlling the chemistry of individual molecules on solid surfaces. We have developed an optical STM technology that combines the STM with light irradiation and detection technologies for our own purpose [1], which allows us to apply the LSP to exploring novel chemical reactions and spectroscopy based on the interaction between the LSP and electronic/vibrational quantum states of a single molecule at the STM junction. We have developed single molecule emission and absorption (Fig. 1(a)) spectroscopy [1] using the interaction between the LSP and a molecule, in which the LSP participates in the exciton formation in a target molecule [2,3]. Combining the emission and absorption spectroscopies, we visualized fluorescence resonance energy transfer between two different molecules [4]. We have also explored the detailed mechanism of single-molecule chemical dynamics induced by the LSP (Fig. 1(b)) [5]. We also applied the LSP to measure tip-enhanced resonance Raman spectra of a single molecule (Fig. 1(c)) [6]. Furthermore, we achieved an ultrahigh-energy resolution photoluminescence measurement of a single molecule using a tunable excitation laser (Fig. 1(d)) [7]. These optical setups enable a real-space measurement of photocurrent pathways at a single molecule (Fig. 1(e)) [8]. In this talk, I will discuss recent issues focusing on single-molecule spectroscopy based on the molecular excitation by localized surface plasmon at the STM junction, which has been applied to exploring the quantum states of a phthalocyanine and its derivatives.

REFERENCES
[1] H. Imada et al., Physical Review Letters, 119 (2017) 013901
[2] K. Miwa et al., Nano Letters, 19 (2019) 2803
[3] K. Kimura et al., Nature, 570 (2019) 210
[4] H. Imada et al., Nature, 538 (2016) 364
[5] E. Kazuma et al., Science, 360 (2018) 521
[6] R.B. Jaculbia et al., Nature Nanotechnology, 15 (2020) 105
[7] H. Imada et al., Science, 373 (2021) 95
[8] M. Imai-Imada et al., Nature 603 (2022) 829

Youngchan Kim

Academic Affiliation: University of Surrey

Title: Quantum biology in fluorescent protein: a new model system to study quantum effects in biology

Abstract:

Quantum effects are usually thought to be too delicate to manifest in biology since random molecular interactions were thought to be instantaneously obliterated quantum coherent molecular interactions occurring in wet biological environments. However, recent biological, chemical, and physical breakthroughs have revealed that subtle quantum effects may shape biological processes and functions, as exemplified by photosynthesis, enzyme catalysed reactions, and magnetic field effects on spin-dependent reactions in biology, to name a few. Studying coherent dipole-dipole coupling between biomolecular systems is challenging but holds many fascinating, fundamental questions that will inspire new ways to better understand and enhance health and medicine. A recent study suggests that the yellow fluorescent proteins, Venus_A206, exhibit room-temperature exciton coupling when they form a dimer. Because cryogenic temperature is not required to observe such quantum effects, genetically engineered fluorescent protein assemblies could inspire a new way towards developing biological quantum technologies, such as quantum-enhanced biosensors. In this talk, I will present the recent progress in studying quantum biology using fluorescent proteins.

Jens Wiebe

Academic Affiliation: University of Hamburg

This lecture is intended for Master and PhD students as well as young Postdocs. After a short historical review of the discoveries of materials which are conventional and unconventional superconductors, I will give an introduction to Cooper pairing and the Bardeen–Cooper–Schrieffer (BCS) theory, the microscopic theory for the description of conventional superconductivity. Then, I will describe the quasiparticle excitation spectrum of such a superconductor and explain how it can be experimentally measured using scanning tunnel spectroscopy, both with normal-metal and superconducting tips. Subsequently, I will talk about the effects of magnetic fields and single magnetic impurities on a superconducting substrate, where the latter leads to the so-called Yu-ShibaRusinov bound states. Finally, I will explain different strategies to tailor a topological superconductor, including the spin chain platform where bands formed by the hybridization of Yu-Shiba-Rusinov states in chains of magnetic atoms in contact to a superconducting surface can host Majorana bound states.

Literature

C. Enss and S. Hunklinger, Low Temperature Physics (Springer 2005)
R. Gross and A. Marx, Festkörperphysik (De Gruyter 2014): unfortunately only in german so far…
Several original publications

Jens Wiebe

Academic Affiliation: University of Hamburg

Title: Search for Large Topological Gaps and Isolated Majorana Bound States in Atom-by-Atom Fabricated Shiba Chains

Abstract:

Paul Weiss

Academic Affiliation: California NanoSystems Institute and Departments of Chemistry & Biochemistry, Bioengineering, and Materials Science & Engineering, UCLA, Los Angeles

Title: Atomically Precise Chemical, Physical, Electronic, and Spin Contacts and Interfaces

Abstract:

One of the key advances in nanoscience and nanotechnology has been our increasing ability to reach the limits of atomically precise structures. By having developed the “eyes” to see, to record spectra, and to measure function at the nanoscale, we have been able to fabricate structures with precision as well as to understand the important and intrinsic heterogeneity of function found in these assemblies. The physical, electronic, mechanical, and chemical connections that materials make to one another and to the outside world are critical. Just as the properties and applications of conventional semiconductor devices depend on these contacts, so do nanomaterials, many nanoscale measurements, and devices of the future. We discuss the important roles that these contacts can play in preserving key transport and other properties. Initial nanoscale connections and measurements guide the path to future opportunities and challenges ahead. Band alignment and minimally disruptive connections are both targets and can be characterized in both experiment and theory. I discuss our initial forays into this area in a number of materials systems.

Daniel Loss

Academic Affiliation: University of Basel

Title: Hole spin qubits for quantum computing in Si and Ge quantum dots

Abstract: 

Hole spin qubits are frontrunner platforms for scalable quantum computers in Si and Ge semiconductors because of their large spin-orbit interaction which enables ultrafast all-electric qubit control at low power. The fastest spin qubits to date are defined in long quantum dots with two tight confinement directions, when the driving field is aligned to the smooth direction [1]. However, in these systems the lifetime of the qubit is strongly limited by charge noise, a major issue in hole qubits. I will give an overview of recent theoretical and experimental results [1-5] that have led to a series of testable predictions such as sweet spots for devices in Si and Ge semiconductors currently implemented in the Swiss National Center on Spin Qubits led by the University of Basel and IBM Zurich.

References

[1] Ultrafast Hole Spin Qubit with Gate-Tunable Spin-Orbit Switch. F. N. M. Froning, L. C. Camenzind, O. A. H. van der Molen, A. Li, E. P. A. M. Bakkers, D. M. Zumbühl, F. R. Braakman; Nature Nanotechnology 16 (2021).

[2] Fully tunable hyperfine interactions of hole spin qubits in Si and Ge quantum dots.
S. Bosco and D.Loss, Phys. Rev. Lett. 127, 190501 (2021).

[3] Hole spin qubits in Si FinFETs with fully tunable spin-orbit coupling and sweet spots for charge noise. S. Bosco, B. Hetényi, and D.Loss; PRX Quantum 2, 010348 (2021).

[4] The germanium quantum information route. G. Scappucci, C. Kloeffel, F. A. Zwanenburg, D. Loss, M. Myronov, J.-J. Zhang, S. De Franceschi, G. Katsaros, and M. Veldhorst; Nat Rev Mater (2020).

[5] A hole spin qubit in a fin field-effect transistor above 4 Kelvin. L. C. Camenzind, S. Geyer, A. Fuhrer, R. J. Warburton, D. M. Zumbühl, A. V. Kuhlmann; Nature Electronics 2022.

Valeria Sheina

Academic Affiliation: C2N, Université Paris – S aclay

Talk title: The development of Quantum Technologies

Abstract:

Quantum spin states constitute a resource for the development of quantum technologies. They have been considered for the realization of quantum computers, quantum simulators and quantum sensors. These long-term goals demand for the identification of appropriate hosts for quantum spin states with long coherence time and compatible with microfabrication technologies. Because of their two-dimensional character that enables an easier localization of the dopants in the material, monoatomic layer of Van-der-Waals materials is of intense interest. My Ph.D. describes experimental works that address two issues in this field. First, the identification of point-defects with interesting spin properties in Van-der-Waals materials; second, the Electrical Detection of Magnetic Resonance (EDMR) in those Van-der-Waals materials.

My work addresses two layered materials possessing spin and valley degrees of freedom: the Br-doped  2H-MoTe2 semiconductor belonging to the transition metal dichalcogenide (TMD) family and graphene. In 2H-MoTe2, we found that the electronic levels of the Br-dopants electronic levels are hybridized to the valleys in the conduction band. This produces spin-valley states where the spin and valley quantum numbers are locked. Moreover, by spin resonance methods, we find that the Br dopant carries an unpaired spin with coherence lifetime reaching 50 ns at the lowest temperature of 4.2 K. This is of practical interest as such states can be manipulated conveniently by electric fields. In graphene, encapsulated in hBN. we show that the spin resonance can be detected by transport measurements and propose a simple model relating the spin-resonant signal to the time average of the perpendicular magnetization component <Mz>.

Mario Ruben

Academic Affiliation: INT, IQMT, Karlsruhe Institute of Technology (KIT) & ISIS, CESQ, University of Strasbourg

Talk title: Quantum Computing with Molecules

Abstract:

Metal complexes will be proposed to acting as active quantum units for Quantum Computing (QC). We report on the implementation of metal complexes into nanometre-sized (single-)molecular spintronic devices by a combination of isotopologue chemistry, bottom-up self-assembly and top-down lithography techniques. The control of the Hilbert space of the molecular quantum magnets on conducting surfaces/electrodes will be shown and persistence of magnetic properties under confinement in Supramolecular Quantum Devices (SMQD) will be proven. The quantum behaviour (e.g.. superposition) of the metal complexes will be addressed at the single molecule level^1-13 to finally implement a quantum algorithm on a TbPc₂-Qudit performing quantum computing  operations.¹⁰ Moreover, we will show that that the components of SMQDs as the Quantum Magnet¹⁴ and the graphene sheets¹⁵ can be made from CO₂ guaranteeing a negative Carbon footprint and sustainability of the molecular approach towards QC.

Franz Josef Giessibl

Academic Affiliation: University of Regensburg

Title: The character of chemical bonds to natural and artificial atoms revealed by atomic force microscopy

Abstract: Atomic force microscopy with CO terminated tips has demonstrated outstanding spatial resolution on organic molecules [1], metallic clusters [2] and many other samples. Experimental evidence and calculations show that the CO tip is chemically inert and probes organic molecules mainly by Paulirepulsion [3]. Thus, images of organic molecules, graphene, etc. observed with a CO tip can be interpreted as a map of the absolute charge density of the sample. The total charge density of a single adatom is approximately given by a Gaussian peak. While single silicon adatoms appear similar to a Gaussian peak when imaged by AFM with a CO terminated tip, copper and iron adatoms adsorbed on Cu(111) and Cu(110) appear as tori [2,4]. Experiments and DFT calculations show that the total charge density of Cu and Fe adatoms is approximately Gaussian–in contrast to a hypothesis that proposes 4spz hybridization of Cu and Fe adatoms on a Cu surface[4]. The bonding strength between the AFM tip and the atoms of the sample depends not only on the chemical identity but also on the coordination-corner atoms in clusters are more reactive than center atoms [5]. Progress in force resolution [6] opens up the fN-regime, enabling to study engineered surface structures such as quantum corrals [7] that can be viewed as artificial atoms. Surprisingly, these artificial atoms interact in a similar way with AFM tips as natural atoms, yet with a force of only 1/1000of what is experienced in natural atoms [8].

References:

[1] L. Gross et al.,Science325, 1110 (2009).

[2] M. Emmrich et al.,Science348, 308 (2015).

[3] N. Moll et al.,New Journal of Physics12, 125020 (2010).

[4] F. Huber et al.,Science366, 235 (2019).

[5] J. Berwanger et al.,Phys.Rev. Lett.124, 096001 (2020).

[6] A. Liebig et al.,New Journal of Physics22, 063040 (2020).

[7]M.F. Crommie, C.P. Lutz, D.M. Eigler,Science262, 218(1993).

[8] F. Stilp, et al.,Science372, 1196 (2021).

Date: June 17, 11:00 (KST)

Location: B1 Jupiter, Center for Quantum Nanoscience