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Kazuyuki Takeda

Publications and source records attributed to Kazuyuki Takeda.

7 recordsLinked to original sources
arXiv2025

Overtone Rabi oscillation of optically polarized triplet electron spins and nuclear hyperpolarization in powder

We report coherent overtone Rabi oscillations of optically-polarized triplet electron spins and nuclear hyperpolarization in powder samples at room temperature. The strong dependence of the single-quantum resonance on the orientation of the zero-field splitting (ZFS) interaction is overcome by coherently driving the significantly narrower overtone transition. Analytical formulas for the overtone lineshape and nutation functions for axially symmetric ZFS interactions are derived. Overtone Rabi oscillations are observed in pentacene-doped \textit{p}-terphenyl and NV$^-$ centers in microdiamonds. For the former, overtone triplet dynamic nuclear polarization using the integrated solid effect leads to $^1$H spin polarization of $0.183\pm0.005$\% at a magnetic field of 0.2~T. The $^1$H NMR polarization is enhanced by a factor of 2600 with respect to thermal equilibrium and reaches a large portion of the randomly oriented microcrystals.

quant-ph↗
arXiv2025

First-order nuclear dipolar order in rotating solids

Nuclear spins' dipolar order is created under magic angle spinning through the first-order process made possible by simultaneous implementation of dipolar recoupling and adiabatic demagnetization in a reference frame reached out through nested transformations, firstly from the laboratory frame into the rotating frame, and then into the spin coordinate system nutating inside its parent frame. In such a nutating frame, both the static and resonantly rotating radio-frequency (RF) fields are invisible, and the re-introduced dipolar interaction provides a secular eigenstate on which dipolar order develops with assist of an additional portion of RF field designed to implement adiabatic demagnetization in the nutating frame.

quant-ph↗
arXiv2021

Speedup of nuclear-spin diffusion in hyperpolarized solids

We propose a correction to the coefficient of nuclear-spin diffusion by a factor $1/\sqrt{1-\overline{p}^{2}}$, where $\overline{p}$ is the average nuclear-spin polarization. The correction, derived by extending the Lowe-Gade theory to low-temperature cases, implies that transportation of nuclear magnetization through nuclear-spin diffusion accelerates when the system is hyperpolarized, whereas for low-polarization the correction factor approaches unity and the diffusion coefficient coincides with the conventional diffusion coefficient valid in the high-temperature limit. The proposed scaling of the nuclear-spin diffusion coefficient can lead to observable effects in the buildup of nuclear polarization by dynamic nuclear polarization.

cond-mat.other↗
arXiv2020

Nuclear Surface Acoustic Resonance with Spin-Rotation Coupling

We show that, under an appropriate out-of-plane static magnetic field, nuclear spins in a thin specimen on a surface acoustic wave (SAW) cavity can be resonantly excited and detected through spin-rotation coupling. Since such a SAW cavity can have the quality factor as high as $10^{4}$ and the mode volume as small as $10^{-2}$ mm$^{3}$ the signal-to-noise ratio in detecting the resonance is estimated to be quite high. We argue that detecting nuclear spin resonance of a single flake of an atomically-thin layer of two-dimensional semiconductor, which has so far been beyond hope with the conventional inductive method, can be a realistic target with the proposed scheme.

cond-mat.mes-hall↗
arXiv2018

Electro-mechano-optical detection of nuclear magnetic resonance

Signal reception of nuclear magnetic resonance (NMR) usually relies on electrical amplification of the electromotive force caused by nuclear induction. Here, we report up-conversion of a radio-frequency NMR signal to an optical regime using a high-stress silicon nitride membrane that interfaces the electrical detection circuit and an optical cavity through the electro-mechanical and the opto-mechanical couplings. This enables optical NMR detection without sacrificing the versatility of the traditional nuclear induction approach. While the signal-to-noise ratio is currently limited by the Brownian motion of the membrane as well as additional technical noise, we find it can exceed that of the conventional electrical schemes by increasing the electro-mechanical coupling strength. The electro-mechano-optical NMR detection presented here opens the possibility of mechanical parametric amplification of NMR signals. Moreover, it can potentially be combined with the laser cooling technique applied to nuclear spins.

quant-ph↗
arXiv2005

Entanglement Witness Derived from NMR Superdense Coding

We show that it is possible to transfer two-bit information via encoding a single qubit in a conventional nuclear magnetic resonance (NMR) experiment with two very weakly polarized nuclear spins. Nevertheless, the experiment can not be regarded as a demonstration of superdense coding by means of NMR because it is based on the large number of molecules being involved in the ensemble state rather than the entanglement of the NMR states. Following the discussions, an entanglement witness, particularly applicable for NMR, is introduced based on separate and simultaneous measurement of the individual nuclear spin magnetizations.

quant-ph↗