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.

September 15, 2023: Paper published on “Wide-field quantitative magnetic imaging of superconducting vortices using perfectly aligned quantum sensors.” Also have a look at the press release.

September 7, 2023: Paper published on “Nitrogen isotope effects on boron vacancy quantum sensors in hexagonal boron nitride.”

July 12, 2023: Podcast on our work of hBN quantum sensor nanoarray. Enjoy!

June 14, 2023: Paper published on “Magnetic field imaging by hBN quantum sensor nanoarray”. Have a look at our press release: Researchers succeed in arranging nanoscale quantum sensors on desired targets. The paper was selected for AIP Publishing Showcase.

May 27, 2023: Paper published on “Demonstration of geometric diabatic control of quantum states“. Have a look at our press release: a new method for quantum control.

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, such as VB in hBN, 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:
hB15N quantum sensor: Sasaki et al. Applied Physics Express 16 (9),095003 (2023). [link][arXiv:2307.04476].
Unexpected optical properties of diamond NV centers: Ito et al. J. Phys. Soc. Jpn. 92, 084701 (2023). [arXiv:2307.04414]
hBN quantum sensor nanoarray: Sasaki et al. Appl. Phys. Lett. 122, 244003 (2023). [arXiv:2301.12645][press release][Selected as AIP Publishing Showcase]
Superconducting vortex imaged: Nishimura et al. Appl. Phys. Lett. 123, 112603 (2023). [press release][arXiv:2304.01024].
Twisted Landau-Zener model demonstrated: Sasaki et al. Phys. Rev. A 107, 053113 (2023). [press release][arXiv:2305.17434]
Enhanced sensitivity of hBN quantum sensor: Gu et al. APEX 16, 055003 (2023).
Lockin thermography: Ogawa et al. J. Phys. Soc. Jpn. 92, 014002 (2023). [arXiv:2212.07616]
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).