Speeding-up a quantum refrigerator via counter-diabatic driving

We study the application of a counter-diabatic driving (CD) technique to enhance the thermodynamic efficiency and power of a quantum Otto refrigerator based on a superconducting qubit coupled to two resonant circuits. Although the CD technique is originally designed to counteract non-adiabatic coherent excitations in isolated systems, we find that it also works effectively in the open system dynamics, improving the coherence-induced losses of efficiency and power. We compare the CD dynamics with its classical counterpart, and find a deviation that arises because the CD is designed to follow the energy eigenbasis of the original Hamiltonian, but the heat baths thermalize the system in a different basis. We also discuss possible experimental realizations of our model.Comment: 9 pages, 8 figure

Simultaneous Wide-field Imaging of Phase and Magnitude of AC Magnetic Signal Using Diamond Quantum Magnetometry

Spectroscopic analysis of AC magnetic signal using diamond quantum magnetometry is a promising technique for inductive imaging. Conventional dynamic decoupling like XY8 provides a high sensitivity of an oscillating magnetic signal with intricate dependence on magnitude and phase, complicating high throughput detection of each parameter. In this study, a simple measurement scheme for independent and simultaneous detection of magnitude and phase is demonstrated by a sequential measurement protocol. Wide-field imaging experiment was performed for an oscillating magnetic field with approximately 100$\mu$m-squared observation area. Single pixel phase precision was $2.1^\circ$ for 0.76$\mu$T AC magnetic signal. Our method enables potential applications including inductive inspection and impedance imaging.Comment: 9 pages, 4 figure

超伝導回路を用いた非平衡開放量子系の研究

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 中村 泰信, 東京大学教授 樽茶 清悟, 東京大学教授 上田 正仁, 大阪大学教授 小林 研介, 東京大学准教授 沙川 貴大University of Tokyo(東京大学

Long Rayleigh length confocal microscope: A fast evaluation tool for obtaining quantum properties of color centers

Color centers in wide band-gap semiconductors, which have superior quantum properties even at room temperature and atmospheric pressure, have been actively applied to quantum sensing devices. Characterization of the quantum properties of the color centers in the semiconductor materials and ensuring that these properties are uniform over a wide area are key issues for developing quantum sensing devices based on color center. In this article, we will describe the principle and performance of a newly developed confocal microscope system with a long Rayleigh length (LRCFM). This system can characterize a wider area faster than the confocal microscope systems commonly used for color center evaluation

Digital signal processing for portable highly sensitive diamond quantum magnetometer

We demonstrate an alternative method of digital signal processing with less computational resources than the Fourier transform. The method uses a digital filter that effectively becomes a sinc filter utilizing the orthogonality of trigonometric functions by multiplication of the acquired data by a trigonometric function. The computational time of the method to compute the signal from n points of data is O(n), whereas the time with Fourier transform is O(n log n). We confirm our method with a large detection volume of the ensemble NV centers. Consequently, we obtained a DC magnetic field sensitivity of 2.4 nT/√Hz.第４回QST国際シンポジウ

Interest consistency can buffer the effect of COVID-19 fear on psychological distress

In the context of a recent outbreak of the coronavirus disease (COVID-19), the present study investigated the buffering effect of grit on the relationship between fear of COVID-19 and psychological distress. The data were collected from 224 Japanese participants (98 females; mean age = 46.56, SD = 13.41) in July 2020. The measures used in this study included the Fear of COVID-19 Scale (FCV-19S), Short Grit Scale, and Depression, Anxiety, and Stress Scale 21 (DASS). The results of mediation analyses revealed significant indirect effects of consistency of interest, a major component of grit, on psychological distress; we also found non-significant indirect effects of perseverance of effort, another major component of grit, on psychological distress. These results suggest that consistency of interest buffers the psychological distress induced by fear of COVID-19. Based on these results, it can be concluded that individuals with higher consistency of interest are less likely to experience worsening of their mental health, even if they experience fear of COVID-19 during the pandemic