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arXiv:2010.00954

Optimal optical polarization of nitrogen-vacancy center with arbitrary waveform pulse

Jixing Zhang, Tianzheng Liu, Lixia, Xu, Guodong Bian, Pengcheng Fan, Mingxin Li, Ning, Zhang, Heng, Yuan

Published Oct 2, 2020• 1 citation
arXivHTMLPDF

Abstract

The current work proposes a method for pulsed-light polarization of nitrogen-vacancy (NV) center electron spin. To evaluate the influence of pulsed spin polarization, we establish a polarization evaluation index based on polarizability and polarization time. Master equation model are utilized to theoretically calculate the spin polarization dynamics under light excitation and the optimal polarization conditions for the conventional methods are obtained. A novel pulsed-light polarization method is proposed by changing the optical pumping rate in the master equation from a fixed value to a time variable and an optimal waveform for proposed method is demonstrated through the variational method, which can simultaneously achieve high polarizability and requires a short polarization time. Hence, the polarization evaluation index is improved by ~10%. Moreover, the proposed method is verified by a pulsed-laser experimental system based on an arbitrary waveform generator. The current report shall expand the application horizon of NV center based quantum sensing.

DOI
10.48550/arxiv.2010.00954

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The current work proposes a method for pulsed-light polarization of nitrogen-vacancy (NV) center electron spin. To evaluate the influence of pulsed spin polarization, we establish a polarization evaluation index based on polarizability and polarization time. Master equation model are utilized to theoretically calculate the spin polarization dynamics under light excitation and the optimal polarization conditions for the conventional methods are obtained. A novel pulsed-light polarization method is proposed by changing the optical pumping rate in the master equation from a fixed value to a time variable and an optimal waveform for proposed method is demonstrated through the variational method, which can simultaneously achieve high polarizability and requires a short polarization time. Hence, the polarization evaluation index is improved by ~10%. Moreover, the proposed method is verified by a pulsed-laser experimental system based on an arbitrary waveform generator. The current report shall expand the application horizon of NV center based quantum sensing.
Abstract In this work, a time-varying pulse waveform spin readout sequence method is proposed to improve the spin readout efficiency of nitrogen-vacancy (NV) centers. The method consists of performing the readout signal-to-noise ratio (SNR) analysis via the construction of a rate equation model of the NV center. We demonstrate a superior performance from the time-varying waveform readout approach and focus on the role of the readout optimization in quantum measurements. A detailed comparison of the readout SNR of the time-varying waveform and conventional waveform is provided. We experimentally demonstrate that the readout SNR is increased by 8% by utilizing an optimized waveform. It is anticipated that the improved method will effectively benefit the sensing capability of NV center ensembles and provide support for high-precision measurements of solid systems.
Initializing a set of qubits to a given quantum state is a basic prerequisite for the physical implementation of quantum-information protocols. Here, we discuss the polarization of the electronic and nuclear spin in a single nitrogen vacancy center in diamond. Our initialization scheme uses a sequence of laser, microwave and radio-frequency pulses, and we optimize the pumping parameters of the laser pulse. A rate equation model is formulated that explains the effect of the laser pulse on the spin system. We have experimentally determined the population of the relevant spin states as a function of the duration of the laser pulse by measuring Rabi oscillations and Ramsey-type free-induction decays. The experimental data have been analyzed to determine the pumping rates of the rate equation model.
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Abstract In this work, a spin readout method using fluorescence dynamics is proposed based on maximum likelihood estimation (MLE) for improving the pulsed spin readout accuracy of nitrogen vacancy (NV) center. This estimation method can saturate the Cramér–Rao bound and enhance the photon-shot-noise-limited spin readout accuracy by 20% compared with conventional photon summation method. By employing a rate equation model of the NV center, the exact solution for the fluorescence dynamics is obtained. Additionally, according to the rate equation model’s relationship with fluorescence dynamics, spin, and pumping light power, a practical MLE readout scheme is furnished, which is able to distinguish spin readout information and classical noise. Compared with the conventional method, the classical noise suppression capability can be improved by 300 times. It is anticipated that the MLE method will effectively benefit sensing capability based on the NV centers even other scalable defect complexes in solid systems.
Implementation of many quantum information protocols requires an efficient initialization of the quantum register. In the present paper, we optimize a population trapping protocol for initializing a hybrid spin register associated with a single nitrogen-vacancy (NV) center in diamond. We initialize the quantum register by polarizing the electronic and nuclear spins of the NV with a sequence of microwave, radio-frequency, and optical pulses. We use a rate equation model to explain the distribution of population under the effect of the optical pulses. The model is compared to the experimental data obtained by performing partial quantum state tomography. To further increase the spin polarization, we propose a recursive protocol with optimized optical pulses. We also discuss the role of the relative values of the nuclear- and electronic-spin pumping rate in achieving the maximum degree of spin polarization.
The nitrogen-vacancy (N-V) center in diamond is a widely used platform for quantum information processing and sensing. The electron-spin state of the N-V center could be initialized, read out optically, and manipulated by resonate microwave fields. In this work, we analyze the dependence of electron-spin initialization on widths of laser pulses. We build a numerical model to simulate this process and to verify the simulation results in experiments. Both simulations and experiments reveal that shorter laser pulses are helpful to the electron-spin polarization. We therefore propose to use extremely short laser pulses for electron-spin initialization. In this new scheme, the spin-state contrast could be improved about 10% in experiments by using laser pulses as short as 4 ns in width. Furthermore, we provide a mechanism to explain this effect, which is due to the occupation time in the meta-stable spin-singlet states of the N-V center. Our new scheme is applicable in a broad range of N-V-based applications in the future.