Research

The sensitivity of a conventional magnetic resonance spectrometer (EPR/NMR) is >10^{10} spins (10 billion spins). Using quantum sensing technique, we improve the sensitivity to the level of a single spin. The quantum sensing-assisted EPR/NMR can be used to study nano-scale magnetism and single molecule structural biology.

1. B. Fortman and S. Takahashi, J. Phys. Chem. A 123, 6350-6355 (2019) [doi]

2. C. Abeywardana, V. Stepanov, F. H. Cho and S. Takahashi, J. Appl. Phys. 120, 123907 (2016); [doi].

Quantum entanglement is the foundation of quantum information science. In quantum sensing, quantum entanglement is a key to improving the sensitivity to the level of the Heisenberg limit. Quantum entanglement is also considered to play a crucial role in the functions of complex systems such as biological systems. We are investigating a methond to detect and control quantum entanglement and its dynamics.

Silicon-vacancy feature in the luminescence of diamond has been found to be particularly sensitive to the charge state of this defect. In particular, the negatively charged Si-V– emits at 738nm, whereas the charge-neutral (Si-V0) emits at 946 nm. Unlike NV emission, which is quite broad (~200 nm) at room temperature due to a wide array of phonon sidebands, the Si-V feature is spectrally narrow. These spectrally narrow photons have a high degree of indistinguishability and are ideal to create entangled photons.

Quantum decoherence is a central concept in physics. Applications such as quantum information science depend on understanding quantum decoherence. There are even fundamental theories proposed that go beyond quantum mechanics. A solid state spin is a great testbed to study fundamental quantum physics. We investigate the nature of quantum decoherence of molecular spins and solid state spins.

1. C. Abeywardana, A. M. Mowson, G. Christou, and S. Takahashi Appl. Phys. Lett. 108, 042401 (2016); [doi].

2. Z. Peng, J. Dallas and S. Takahashi, J. Appl. Phys. 128, 054301 (2020); [doi] [arXiv].

3. C. Abeywardana, Z. Peng, L. C. Mugica, E. Kleinsasser, K.-M. C. Fu and S. Takahashi, Appl. Mag. Res. 48, 571-577 (2017); [doi].

4. S. Takahashi, I. S. Tupitsyn, J. van Tol, C. C. Beedle, D. N. Hendrickson, and P. C. E. Stamp, Nature 476, 76 (2011); [doi].

5. V. Stepanov and S. Takahashi Phys. Rev. B 94, 024421 (2016); [doi].

6. Z.-H. Wang and S. Takahashi Phys. Rev. B 87, 115122 (2013); [doi].

Smilar to nuclear magnetic resonance (NMR), pulsed electron spin resonance (ESR) is highly advantageous at high magnetic fields (HF), as the higher field clearly separates spin systems with similar g values, improves spin polarization, increases sensitivity for molecules in motion, and offers generally greater control over the underlying spin dynamics. On the other hand, pulsed HF ESR often has the disadvantage of long pulse times due to low HF microwave power. The low microwave power limits the excitation bandwidth and, consequently, the sensitivity of pulsed ESR measurements. NV-ESR can overcome this limitation and improve the sensitivity of HF ESR drastically. However, only a few investigations of NV centers have been performed at high magnetic fields, and NV-ESR has not been demonstrated at a high magnetic field. Recently, we have built a high-field NV-ESR spectrometer and demonstrated NV-ESR at the highest magnetic field to date, 4.2 Tesla, using both ensemble and single NV centers. NV-ESR at this field would allow for spectral separation and clear identification of signals that severely overlap at low fields.

1. B. Fortman, L. Mugica-Sanchez, N. Tischler, C. Selco, Y. Hang, K. Holczer and, S. Takahashi, J. Appl. Phys. 130, 083901 (2021) [doi]

2. B. Fortman, J. Pena, K. Holczer and S. Takahashi, Appl. Phys. Lett. 116, 174004 (2020) [doi] [arXiv].

3. V. Stepanov, F. H. Cho, C. Abeywardana and S. Takahashi, Appl. Phys. Lett. 106, 063111 (2015); [doi].

A high-frequency/high-field (HF) ESR is highly advantageous for finer spectral resolution, faster time resolution and higher sensitivity with higher degree of spin polarization. It also has been shown that HF ESR enables extending spin coherence of various systems. We have constructed a HF ESR spectrometer (0-12.1 Tesla and 107-120/215-240 GHz) in the lab [1,2]. Among several HF ESR spectrometers in the world, our unique specrometer is capable to utilize multiple frequecies of microwave pulses for double electron-electron resonance and other advanced pulsed ESR experiments.

1. F. H. Cho, V. Stepanov and S. Takahashi, Rev. Sci. Instrum. 85, 075110 (2014); [doi].

2. R. D. Akiel, V. Stepanov and S. Takahashi, Cell Biochem. Biophys. 75, 151-157 (2016); [doi].