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Extension of Spin Dephasing Time of Continuously Excited Ensemble Nitrogen Vacancy Centers by Double-Quantum Ramsey Magnetometry with Spin Bath Driving

伊久哉 藤崎, Ikuya Fujisaki, 裕太 荒木, Yuta Araki, 雄治 波多野, Yuji Hatano, T. Sekiguchi, Hiromitsu Kato, Sninobu Onoda, 孝之 岩崎, Takayuki Iwasaki, 睦子 波多野, Takayuki Iwasaki, Mutsuko Hatano

Published Jul 1, 2023• 0 citations
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Crossed two-layer coplanar-waveguide circuit for extending spin dephasing time T2* of ensemble NV centers in a bulk diamond

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The nitrogen-vacancy (NV) center in diamond is extensively studied for a next-generation high-sensitivity magnetometer. The DC magnetic sensitivity can be improved by extending the inhomogeneous spin dephasing time through suppressing the effects of inhomogeneous fluctuations or by increasing the number of effective NV centers through expanding the sensor volume. It has been demonstrated that strain-induced dephasing can be suppressed by double quantum (DQ) technique with two-tone microwaves (MW), and spin bath-induced dephasing can be suppressed by spin bath drive (SBD) technique with multi-tone radio-frequency (RF) to drive the P1 centers. To combine these T2* -extension techniques with a bulk diamond, it is necessary to apply MW and RF uniformly to the sample. A coplanar waveguide (CPW) circuit has been reported to be useful for uniform microwave irradiation to a bulk sample. In this study, we reports the newly designed and fabricated a cross-aligned two-layer CPW circuit.

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Quantum magnetic sensors based on nitrogen vacancy (NV) centers are expected to be used for various biological and medical applications. Continuously excited (CE) Ramsey magnetometry is one of the most sensitive measurement protocols and has the potential to improve the sensitivity of sensors using additional quantum manipulations to extend the spin dephasing time. In a typical ensemble NV measurement, the spin dephasing time is limited by inhomogeneous coupling. To overcome this limitation, a magnetometry that extends the CE Ramsey protocol with a double‐quantum (DQ) Ramsey sequence and spin bath driving is developed. It is demonstrated that the electric noise due to the spatial inhomogeneity of the crystal strain is cancelled out by the DQ Ramsey, and the magnetic noise due to the P1 centers was suppressed by spin bath driving. Compared to the conventional CE Ramsey, the CE‐DQ Ramsey with spin bath driving effectively doubles the gyromagnetic ratio and yields a twofold extension of , corresponding to a fourfold enhancement of the photon‐shot‐noise limited sensitivity.
Nitrogen-vacancy (NV) centers in diamond have found broad applications owing to optical spin initialization and readout as well as long spin coherence time at room temperature.1 Recently, we have reported the construction of a pulsed optically detected magnetic resonance (ODMR) system based on double quantum (DQ) Ramsey magnetometry with lock-in (LI) detection towards DC magnetic field sensitivity sufficient for magnetoencephalography.2 The LI detection of fluorescence allowed reduction of the noise floor, removal of the signal offset, and real-time monitoring of the magnetic field. Beyond the CW-ODMR, where spectral broadening and contrast reduction are induced by high-power excitation, the DQ-Ramsey is expected to have highersensitivity, as it allows extension of spin dephasing time T2 * and increase of contrast and fluorescence rates.2 In practice, however, the magnetic sensitivity depends also on how the optical excitation is applied. In this study, we report the excitation power stabilization by reducing the phase noise and the effect of the excitation power on the fluorescence saturation behavior.
The nitrogen-vacancy (NV) center in diamond is extensively studied for a next-generation high-sensitivity magnetometer. The DC magnetic sensitivity can be improved by extending the inhomogeneous spin dephasing time through suppressing the effects of inhomogeneous fluctuations or by increasing the number of effective NV centers through expanding the sensor volume. It has been demonstrated that strain-induced dephasing can be suppressed by double quantum (DQ) technique with two-tone microwaves (MW), and spin bath-induced dephasing can be suppressed by spin bath drive (SBD) technique with multi-tone radio-frequency (RF) to drive the P1 centers. To combine these T2* -extension techniques with a bulk diamond, it is necessary to apply MW and RF uniformly to the sample. A coplanar waveguide (CPW) circuit has been reported to be useful for uniform microwave irradiation to a bulk sample. In this study, we reports the newly designed and fabricated a cross-aligned two-layer CPW circuit.