표면위의 양자 시스템에 대한 이론연구

소개

The QNS Theory Team has two goals:

  1. To be just one door away for every experimentalist and aid in the explanation of new discoveries
  2. To guide experimentalists in our search for highly coherent quantum spin systems on surfaces and interfaces

The fast feedback in this integrated approach with theory and experiment has proven advantageous in a research field that pushes the boundaries of knowledge using quantum science at the atomic scale.

We rely on a multi-scale approach to study  surface spin systems:

For large scale systems we utilize ab initio calculations in the framework of Density Functional Theory (DFT). This method is suitable for treating a large variety of surface systems such as atoms and molecules at equal footing, but has some drawbacks when describing correlated phenomena such as magnetism at the nanoscale due to approximations made in the implementation of DFT.

To overcome these limitations, QNS and collaborators have developed tools that go beyond the DFT mean field description which we call “DFT+Multiplet”, which allows us to recover the true many-body character of the wavefunction. Using DFT+Multiplet we are able to accurately explore the landscape of magnetic energies of small to mid-size system. [1]

Last, we aim to  understand quantum coherence of  surface spin systems. To achieve this we  use open quantum systems simulations which allow us to accurately track the time evolution of small systems consisting of a few spins. We employ microscopic quantum master equations to accurately model the physics of an ESR-STM junction, [2] as well as more phenomenological approaches to model quantum control and quantum entanglement. [3]

Most of our work can be performed in-house on our mid-size high-performance computer cluster. We employ publicly available open-source codes and actively engage in method and code development.

We aim to make QNS a global hub for theoretical studies of quantum phenomena on surfaces and maintain a large number of active collaborations ranging from theory to experiment with leading experts in the field domestically and internationally.

Figure 1: The QNS Theory team provides quantitative models for surface spin systems including time evolution (open quantum systems simulations) and spectroscopy (transport simulations). Rapid feedback from the experiment is used to improve our models in a theory-experiment feedback loop

Longer-term Goals

  • Find highly coherent surface quantum systems that are suitable for the realization of high-fidelity quantum control
  • Develop theoretical understanding of quantum coherence, with emphasis on mitigating decoherence
  • Explore the quantum properties of other surface systems such as carbon-based 2D materials

Near-term Goals

  • Utilize d and f electron systems to improve quantum coherence
  • Explore different materials systems for long  lifetime and coherence times
  • Guiding experiments in QNS towards ideal surface spin systems
  • Expand the QNS global hub with long-term and short-term visitors

References

  1. Christoph Wolf and Fernando Delgado and José Reina and Nicolás Lorente (2020): Efficient Ab Initio Multiplet Calculations for Magnetic Adatoms on MgO. In: Journal of Physical Chemistry A, vol. 124, no. 11, pp. 2318–2327, 2020, ISSN: 15205215.
  2. Jose Reina-Gálvez and Christoph Wolf and Nicolás Lorente (2023): Many-body nonequilibrium effects in all-electric electron spin resonance. In: Physical Review B, vol. 107, no. 23, pp. 235404, 2023, ISSN: 2469-9950.
  3. Rik Broekhoven and Curie Lee and Soo-hyon Phark and Sander Otte and Christoph Wolf (2024): Protocol for certifying entanglement in surface spin systems using a scanning tunneling microscope. In: npj Quantum Information, vol. 10, no. 1, pp. 92, 2024, ISSN: 2056-6387.