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arXiv:1912.06284 · Photonics Research

Pulse-width-induced polarization enhancement of optically pumped N-V electron spin in diamond

Yumeng Song, Yu Peng Tian, Zhiyi Hu, Feifei Zhou, Tengteng Xing, Dawei Lu, Bing Chen, Ya Wang, Nanyang Xu, Jiangfeng Du

Published Jun 4, 2020• 32 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1364/prj.386983

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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.
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.
The electron spin of the negatively charged the nitrogen vacancy center $({\mathrm{NV}}^{\ensuremath{-}}$) in diamond can be optically polarized through intersystem crossing, which enables the defect to be used for quantum computation and metrology. In this work, we studied the electron spin depolarization effect of the NV center induced by charge state conversion, which was proven to be a spin-independent process. The spin-state initialization fidelity was largely affected by the charge state conversion process. As a result, the optical polarization of the electron spin decreased about 1414%(31%14) with a high-power continuous-wave (pulsed) green laser. Moreover, the undefined fluorescence anomalous saturation effect of the NV center was analyzed and explained in detail based on the spin depolarization. The results demonstrated that a weak laser should be used for initialization of the NV center. In addition, the power and polarization of a laser for NV spin detection should be carefully adjusted to obtain the highest fluorescence signal. Our work also provided information that can increase the understanding of the charge state conversion and spin polarization processes of the NV center for quantum information and sensing.
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.
Nitrogen-vacancy (NV) color centers in diamond serve as promising atomic spin systems for measurement applications requiring high accuracy and sensitivity. A key challenge in NV-based quantum sensing is minimizing spin readout noise to approach the standard quantum limit (SQL). Based on a six-level model, this work analyze the dependence of NV-based quantum sensing performance, including spin state readout noise and signal-to-noise ratio (SNR), on controllable parameters such as the Purcell factor and excitation laser pulse characteristics. This study demonstrates that a shorter excitation pulse duration results in a higher saturation value of ground-state spin polarization, while the total time required for the polarization process remains constant. Additionally, the spin readout noise does not improve monotonically with decreasing excitation pulse duration; instead, it initially decreases and subsequently increases as the pulse duration varies. The spin readout noise reaches its optimal level when the pulse duration is 3 ns. Furthermore, no positive correlation exists between the signal-to-noise ratio (SNR) and the Purcell factor, and there is also an optimal value for SNR. When the pulse duration ranges from 1 ns to 40 ns, the variation in SNR is relatively insignificant. This research offers a novel perspective for enhancing the performance of quantum sensing based on diamond defects, such as nitrogen-vacancy (NV) centers.
The nitrogen-vacancy (NV) center in diamond has been developed as a promising platform for quantum sensing, especially for magnetic field measurements in the nano-tesla range with a nano-meter resolution. Optical spin readout performance has a direct effect on the signal-to-noise ratio (SNR) of experiments. In this work, we introduce an online optimization method to customize the laser waveform for readout. Both simulations and experiments reveal that our new scheme optimizes the optically detected magnetic resonance in NV center. The SNR of optical spin readout has been witnessed a 44.1% increase in experiments. In addition, we applied the scheme to the Rabi oscillation experiment, which shows an improvement of 46.0% in contrast and a reduction of 12.1% in mean deviation compared to traditional constant laser power SNR optimization. This scheme is promising to improve sensitivities for a wide range of NV-based applications in the future.
Initializing quantum registers with high fidelity is a fundamental precondition for many applications like quantum information processing and sensing. The electronic and nuclear spins of a nitrogen-vacancy (NV) center in diamond form an interesting hybrid quantum register that can be initialized by a combination of laser, microwave, and radio-frequency pulses. However, the laser illumination, which is necessary for achieving electron spin polarization, also has the unwanted side effect of depolarizing the nuclear spin. Here we study how the depolarization dynamics of the 14N^{14}\mathrm{N}14N nuclear spin depends on the laser wavelength. We show experimentally that excitation with an orange laser (594 nm) causes significantly less nuclear spin depolarization compared to the green laser (532 nm) typically used for excitation and hence leads to higher nuclear spin polarization. This could be because orange light excitation inhibits ionization of NV0{\mathrm{NV}}^{0}NV0 into ${\mathrm{NV}}^{\ensuremath{-}}$ and therefore suppresses one source of noise acting on the nuclear spin.