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Precise Condensed-matter Physics

We are interested in various phenomena in solid-state devices, especially quantum many-body effects and non-equilibrium phenomena. In particular, we aim to observe and control quantum phenomena with high precision, to challenge experiments that would have been impossible in the past, and to discover new wonders. As a prime example of our past research, please look at our review paper on non-equilibrium current fluctuations in mesoscopic systems.

Our current central topic is an ultra-precise measurement of physical properties using quantum sensors, namely a single quantum spin microscope using color centers such as diamond NV centers.

Quantum spin microscopy

A measurement technique based on the principles of quantum mechanics is called quantum sensing. The use of quantum mechanics allows us to perform precise measurements that were previously impossible. We are interested in the potential of color centers as quantum sensors. The color centers are lattice defects that exist stably in crystals. In the diamond NV center, a representative color center, two neighboring carbon atoms are replaced by a pair of nitrogen (nitrogen) and an atomic vacancy (vacancy), which has a unique quantum level inside (see the right figure).

Recent studies have shown that the quantum states of electrons and nuclear spins in NV centers are retained for a long time, which helps develop new measurement techniques. Precise measurement of the quantum levels in NV centers makes it possible to measure the magnetic field and temperature felt by NV centers with ultra-high precision. NV centers can be called atomic-sized single quantum spin sensors in this respect. This idea first appeared in 2008. By developing a single quantum spin microscope using NV centers, we hope to observe the magnetic properties and dynamics of materials as if we were watching a movie.

Exploring the properties of materials using NV centers and other color centers is expected to make significant progress. Many essential and fascinating unsolved topics in physics are waiting for us, such as quantum liquid crystals, non-equilibrium transport, spin glass, topological edge states, and persistent currents.

Recent papers related to quantum sensors:
hBN quantum sensor nanoarray: Sasaki et al. arXiv:2301.12645.
Lockin thermography: Ogawa et al. J. Phys. Soc. Jpn. 92, 014002 (2023).
Machine learning & quantum sensing: Tsukamoto et al. Sci. Rep. 12, 13942 (2022).
Floquet engineering: Nishimura et al. Phys. Rev. Appl. 18, 064023 (2022).
Efficient spin readout: Nakamura et al. AIP Advances 12, 055215 (2022).
Magnetic field imaging: Tsukamoto et al., Appl. Phys. Lett. 118, 264002 (2021).