@article{Cho2024,

title = {A continuous-wave and pulsed X-band electron spin resonance spectrometer operating in ultra-high vacuum for the study of low dimensional spin ensembles},

author = {Franklin H Cho and Juyoung Park and Soyoung Oh and Jisoo Yu and Yejin Jeong and Luciano Colazzo and Lukas Spree and Caroline Hommel and Arzhang Ardavan and Giovanni Boero and Fabio Donati},

url = {https://pubs.aip.org/rsi/article/95/6/063904/3297917/A-continuous-wave-and-pulsed-X-band-electron-spin},

doi = {10.1063/5.0189974},

issn = {0034-6748},

year  = {2024},

date = {2024-06-01},

urldate = {2024-06-01},

journal = {Review of Scientific Instruments},

volume = {95},

number = {6},

publisher = {AIP Publishing},

abstract = {We report the development of a continuous-wave and pulsed X-band electron spin resonance (ESR) spectrometer for the study of spins on ordered surfaces down to cryogenic temperatures. The spectrometer operates in ultra-high vacuum and utilizes a half-wavelength microstrip line resonator realized using epitaxially grown copper films on single crystal Al2O3 substrates. The one-dimensional microstrip line resonator exhibits a quality factor of more than 200 at room temperature, close to the upper limit determined by radiation losses. The surface characterizations of the copper strip of the resonator by atomic force microscopy, low-energy electron diffraction, and scanning tunneling microscopy show that the surface is atomically clean, flat, and single crystalline. Measuring the ESR spectrum at 15 K from a few nm thick molecular film of YPc2, we find a continuous-wave ESR sensitivity of 2.6 × 1011 spins/G · Hz1/2, indicating that a signal-to-noise ratio of 3.9 G · Hz1/2 is expected from a monolayer of YPc2 molecules. Advanced pulsed ESR experimental capabilities, including dynamical decoupling and electron-nuclear double resonance, are demonstrated using free radicals diluted in a glassy matrix.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{peng_investigation_2019,

title = {Investigation of near-surface defects of nanodiamonds by high-frequency EPR and DFT calculation},

author = {Z. Peng and T. Biktagirov and F. H. Cho and U. Gerstmann and S. Takahashi},

url = {https://pubs.aip.org/jcp/article/150/13/134702/197109/Investigation-of-near-surface-defects-of},

doi = {10.1063/1.5085351},

issn = {0021-9606, 1089-7690},

year  = {2019},

date = {2019-04-01},

urldate = {2024-11-16},

journal = {The Journal of Chemical Physics},

volume = {150},

number = {13},

pages = {134702},

abstract = {Nanodiamonds (NDs) hosting nitrogen-vacancy (NV) centers are a promising platform for quantum sensing applications. Sensitivity of the applications using NV centers in NDs is often limited due to the presence of paramagnetic impurity contents near the ND surface. Here, we investigate near-surface paramagnetic impurities in NDs. Using high-frequency (HF) electron paramagnetic resonance spectroscopy, the near-surface paramagnetic impurity within the shell of NDs is probed and its g-value is determined to be 2.0028(3). Furthermore, HF electron-electron double resonance-detected nuclear magnetic resonance spectroscopy and a first principles calculation show that a possible structure of the near-surface impurity is the negatively charged vacancy V−. The identification of the near-surface impurity by the present investigation provides a promising pathway to improve the NV properties in NDs and the NV-based sensing techniques.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{feng_gradient-based_2018,

title = {Gradient-based closed-loop quantum optimal control in a solid-state two-qubit system},

author = {Guanru Feng and Franklin H. Cho and Hemant Katiyar and Jun Li and Dawei Lu and Jonathan Baugh and Raymond Laflamme},

url = {https://link.aps.org/doi/10.1103/PhysRevA.98.052341},

doi = {10.1103/PhysRevA.98.052341},

issn = {2469-9926, 2469-9934},

year  = {2018},

date = {2018-11-01},

urldate = {2018-11-01},

journal = {Physical Review A},

volume = {98},

number = {5},

pages = {052341},

abstract = {Quantum optimal control can play a crucial role in realizing a set of universal quantum logic gates with error rates below the threshold required for fault tolerance. Open-loop quantum optimal control relies on accurate modeling of the quantum system under control and does not scale efficiently with system size. These problems can be avoided in closed-loop quantum optimal control, which utilizes feedback from the system to improve control fidelity. In this paper, two gradient-based closed-loop quantum optimal control algorithms, the hybrid quantum-classical approach (HQCA) described by Li et al. [Phys. Rev. Lett. 118, 150503 (2017)] and the finite-difference (FD) method, are experimentally investigated and compared to the open-loop quantum optimal control utilizing the gradient ascent method. We employ a solid-state ensemble of coupled electron-nuclear spins serving as a two-qubit system. Specific single-qubit and two-qubit state preparation gates are optimized using the closed-loop and open-loop methods. The experimental results demonstrate the implemented closed-loop quantum control outperforms the open-loop control in our system. Furthermore, simulations reveal that HQCA is more robust than the FD method to gradient noise which originates from measurement noise in this experimental setting. On the other hand, the FD method is more robust to control field distortions coming from nonideal hardware.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{feng_estimating_2016,

title = {Estimating the Coherence of Noise in Quantum Control of a Solid-State Qubit},

author = {Guanru Feng and Joel J. Wallman and Brandon Buonacorsi and Franklin H. Cho and Daniel K. Park and Tao Xin and Dawei Lu and Jonathan Baugh and Raymond Laflamme},

url = {https://link.aps.org/doi/10.1103/PhysRevLett.117.260501},

doi = {10.1103/PhysRevLett.117.260501},

issn = {0031-9007, 1079-7114},

year  = {2016},

date = {2016-12-01},

urldate = {2016-12-01},

journal = {Physical Review Letters},

volume = {117},

number = {26},

pages = {260501},

abstract = {To exploit a given physical system for quantum information processing, it is critical to understand the different types of noise affecting quantum control. Distinguishing coherent and incoherent errors is extremely useful as they can be reduced in different ways. Coherent errors are generally easier to reduce at the hardware level, e.g., by improving calibration, whereas some sources of incoherent errors, e.g., 𝑇2* processes, can be reduced by engineering robust pulses. In this work, we illustrate how purity benchmarking and randomized benchmarking can be used together to distinguish between coherent and incoherent errors and to quantify the reduction in both of them due to using optimal control pulses and accounting for the transfer function in an electron spin resonance system. We also prove that purity benchmarking provides bounds on the optimal fidelity and diamond norm that can be achieved by correcting the coherent errors through improving calibration.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}