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Journal of Physics D Applied Physics

An improved spin readout for nitrogen vacancy center ensemble based on a maximum likelihood estimation method

Jixing Zhang, Lixia Xu, Tao Shi, Guodong Bian, Pengcheng Fan, Mingxin Li, Peirong Chen, Chang Xu, Ning Zhang, Heng Yuan

Published Jul 21, 2020• 14 citations
Publisher

Abstract

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.

DOI
10.1088/1361-6463/aba7de

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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.
This article introduces a real-time Bayesian estimation algorithm aimed at enhancing the spin readout efficiency of the nitrogen vacancy (NV) center ensemble in the diamond. By integrating both the prior probability distribution and the fluorescence likelihood function, stemming from the implementation of the NV center dynamics model, we offered an innovative solution to surpass the Cramer–Rao lower bound of the readout variance and improve the readout efficiency. The proposed real-time Bayesian estimation readout algorithm was experimentally realized by combining high-performance acquisition and processing hardware, and the Rabi oscillation experiments divulged that the signal-to-noise ratio of our approach was improved by 28.6%. This research illustrates the potential of the Bayesian estimation readout to enhance the NV ensemble's sensing capabilities and support the development of compact and scalable quantum sensors devices on a monolithic platform.
The optical-noise-limited spin readout sensitivity determines the precision of quantum measurement based on nitrogen-vacancy (NV) center. This article investigates the fluorescence dynamics of NV centers by solving the optical rate equations and obtains complete theoretical formulas for the existing optical spin readout method. A transfer coefficient of optical noise to signal noise in the existing differential methods at different frequencies is introduced so as to analyze the optical noise suppression ability and the signal-to-noise ratio (SNR) results under the influence of photon shot noise and optical noise. To further reduce the influence of optical noise on the signal, we propose a modified method to minimize the transfer coefficient by adding a first-order compensation term. Compared with conventional methods, our modified method showed a twofold optical noise suppression ability improvement in the measurement frequency bandwidth. The experiment proves that the final SNR is increased by 43.4% for a long-term measurement. This modified method should lead to immediate improvements in pulsed spin readout of NV center ensembles without extra instrumentation for applications in magnetic field, electric field, and temperature measurements.
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.
Nitrogen-vacancy (NV) centers in diamond have been used in recent years for a wide range of applications, from nanoscale NMR to quantum computation. These applications depend strongly on the efficient readout of the NV center's spin state, which is currently limited. Here we suggest a method of reading the NV center's spin state, using the weak optical transition in the singlet manifold. We numerically calculate the number of photons collected from each spin state using this technique, and show that an order of magnitude enhancement in spin-readout signal-to-noise ratio is expected, making single-shot spin readout within reach. Thus, this method could lead to an order of magnitude enhancement in sensitivity for ubiquitous NV-based sensing applications, and remove a major obstacle from using NVs for quantum information processing.
Nitrogen vacancy centers in diamond are among the leading solid state quantum platforms, offering exceptional spatial resolution and sensitivity for applications such as magnetic field sensing, thermometry, and bioimaging. However, in high background environments,such as those encountered in in vitro diagnostics, the performance of NV based sensors can be compromised by strong background fluorescence, particularly from substrates such as nitrocellulose. In this work, we analytically and experimentally investigate the use of pulsed laser excitation combined with time gating techniques to suppress background fluorescence and enhance the signal to noise ratio in NV based quantum sensing, with an emphasis on spin enhanced biosensing. Through experimental studies using mixed ensembles of silicon vacancy and NV centers in bulk diamond, as well as fluorescent nanodiamonds on NC substrates, we demonstrate significant improvements in NV spin resonance visibility, demonstrated by an increase of the SNR by up to 4x, and a resulting measurement time reduction by 16x. The presented technique and results here can help significantly increase the readout efficiency and speed in future applications of NV centers in high background environments, such as in IVD, where the NV centers are used as a fluorescent label for biomolecules.
Nitrogen-vacancy centers in diamond allow coherent spin state manipulation and optical readout at room temperature, which has powerful applications in nanoscale sensing. Nanophotonic structures such as plasmonic waveguides, nanoantennae, metamaterials, and metasurfaces can enhance the detected fluorescence rate from such broadband emitters. The fluorescence of the coupled emitter is directed into confined plasmonic modes with high photonic density of states. However, an accurate spin readout requires both high photon counts and a strong contrast between the spin states, both of which can be influenced by the Purcell effect. We introduce a novel method for measuring the spin contrast in large nitrogen-vacancy ensembles. We use this method to study how the photonic density of states must be engineered in order to minimize the uncertainty of spin readout in dense NV ensembles. We describe these results using a kinetic model of the nitrogen-vacancy’s internal dynamics.