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arXiv:1908.10147 · Japanese Journal of Applied Physics

Single spin detection with entangled states

Hideaki Hakoshima, Yuichiro Matsuzaki

Published Dec 24, 2019• 5 citations
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Abstract

Abstract Single spin detection is an interesting subject in the field of quantum metrology. Many experiments regarding single spin measurements have been performed recently. However, to detect weak magnetic fields from a single spin, it is necessary to take an extremely long measurement time toward realizing a reasonably high signal-to-noise ratio. In this paper, we propose an alternative method to accomplish rapid and accurate detection of a single spin with entangled states. While entanglement is a well-known resource to improve the signal-to-noise ratio when we measure globally applied magnetic fields, we examine a strategy to exploit the entanglement to detect spatially inhomogeneous magnetic fields from a target single spin. We find that entanglement significantly enhances the signal-to-noise ratio for single spin detection, even under the effect of realistic noise. Our results will contribute a great deal to the development of practical single spin detection.

DOI
10.7567/1347-4065/ab656a

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Abstract Single spin detection is an interesting subject in the field of quantum metrology. Many experiments regarding single spin measurements have been performed recently. However, to detect weak magnetic fields from a single spin, it is necessary to take an extremely long measurement time toward realizing a reasonably high signal-to-noise ratio. In this paper, we propose an alternative method to accomplish rapid and accurate detection of a single spin with entangled states. While entanglement is a well-known resource to improve the signal-to-noise ratio when we measure globally applied magnetic fields, we examine a strategy to exploit the entanglement to detect spatially inhomogeneous magnetic fields from a target single spin. We find that entanglement significantly enhances the signal-to-noise ratio for single spin detection, even under the effect of realistic noise. Our results will contribute a great deal to the development of practical single spin detection.
Single spin detection is one of the important tasks in the field of quantum metrology.Many experiments about the single spin detection has been performed.However, due to the weak magnetic fields from the single spin, a long measurement time is required to achieve a reasonably high signalto-noise ratio.Here, we propose an alternative way to realize rapid and accurate single spin detection with entangled states.While it is known that entanglement can improve the sensitivity to measure globally applied magnetic fields, we investigate a strategy to use the entanglement for detecting spatially inhomogeneous magnetic fields from the target single spin.We show that the entanglement significantly increases the signal to noise ratio for the single spin detection even under the effect of realistic noise.Our results pave the way for practical single spin detection.
The efficient detection of a single spin is a significant goal of improving the sensitivity of quantum magnetic-field sensors. Recent results show that a specific type of entanglement such as Greenberger-Horne-Zeilinger (GHZ) states can be used as a resource to improve the performance of single spin detection. However, scalable generation of the GHZ states is experimentally difficult to realize. It is desirable to use a practical entangled state that can be easily generated. In this paper, we propose the efficient detection of a single spin with Dicke states. We show a way to prepare and measure Dicke states via a global control. Moreover, we investigate how dephasing due to unwanted coupling with the environment affects the performance of our proposal, and show that single spin detection with Dicke states with dephasing has a significant advantage over the classical strategy with separable states. Our results are important toward realizing entanglement enhanced single spin detection.
Single spin detection is a key objective in the field of metrology. There have been many experimental and theoretical investigations for the spin detection based on the use of probe spins. A probe spin shows the precession due to dipole-dipole interaction from a target spin, and measurement results of the probe spin allow us to estimate the state of the target spin. Here, we investigate performance of single-spin detection when using an ensemble of probe spins. Even though the ensemble of probe spins inevitably induces projection noise that could hinder the signal from the target spin, optimization of the configuration of the spin ensemble improves the sensitivity such that enhancement of the signal can be much larger than the projection noise. The probe-spin ensemble is especially useful at a large distance from the target spin, where it is difficult for a single spin to read out the target spin within a reasonable repetition time. Our results pave the way for a new strategy to realize efficient single-spin detections.
Entanglement is a resource to improve the sensitivity of quantum sensors. In an ideal case, using an entangled state as a probe to detect target fields, we can beat the standard quantum limit by which all classical sensors are bounded. However, since entanglement is fragile against decoherence, it is unclear whether entanglement-enhanced metrology is useful in a noisy environment. Its benefit is indeed limited when estimating the amplitude of DC magnetic fields under the effect of parallel Markovian decoherence, where the noise operator is parallel to the target field. In this paper, on the contrary, we show an advantage to using an entanglement over the classical strategy under the effect of parallel Markovian decoherence when we try to detect AC magnetic fields. We consider a scenario to induce a Rabi oscillation of the qubits with the target AC magnetic fields. Although we can, in principle, estimate the amplitude of the AC magnetic fields from the Rabi oscillation, the signal becomes weak if the qubit frequency is significantly detuned from the frequency of the AC magnetic field. We show that, by using the GHZ states, we can significantly enhance the signal of the detuned Rabi oscillation even under the effect of parallel Markovian decoherence. Our method is based on the fact that the interaction time between the GHZ states and AC magnetic fields scales as 1/L1/L1/L to mitigate the decoherence effect where LLL is the number of qubits, which contributes to improving the bandwidth of the detectable frequencies of the AC magnetic fields. Our results open up the way for new applications of entanglement-enhanced AC magnetometry.
Entanglement is a resource to improve the sensitivity of quantum sensors. In an ideal case, using an entangled state as a probe to detect target fields, we can beat the standard quantum limit by which all classical sensors are bounded. However, since entanglement is fragile against decoherence, it is unclear whether entanglement-enhanced metrology is useful in a noisy environment. Its benefit is indeed limited when estimating the amplitude of dc magnetic fields under the effect of parallel Markovian decoherence, where the noise operator is parallel to the target field. In this paper, on the contrary, we show an advantage to using an entanglement over the classical strategy under the effect of parallel Markovian decoherence when we try to detect ac magnetic fields. We consider a scenario to induce a Rabi oscillation of the qubits with the target ac magnetic fields. Although we can, in principle, estimate the amplitude of the ac magnetic fields from the Rabi oscillation, the signal becomes weak if the qubit frequency is significantly detuned from the frequency of the ac magnetic field. We show that, by using the Greenberger-Horne-Zeilinger (GHZ) states, we can significantly enhance the signal of the detuned Rabi oscillation even under the effect of parallel Markovian decoherence. Our method is based on the fact that the interaction time between the GHZ states and ac magnetic fields scales as 1/L1/L1/L to mitigate the decoherence effect, where LLL is the number of qubits, which contributes to improving the bandwidth of the detectable frequencies of the ac magnetic fields. Our results pave the way for new applications of entanglement-enhanced ac magnetometry.
Abstract Recently, there have been significant developments to detect nuclear spins with nitrogen vacancy (NV) centers in diamond. However, due to the nature of the short range dipole–dipole interaction, it takes a long time to detect distant nuclear spins with the NV centers. Here, we propose a rapid detection of nuclear spins with an entanglement between the NV centers. We show that the necessary time to detect the nuclear spins with the entanglement is several orders of magnitude shorter than that with separable NV centers. Our results pave the way for new applications in nanoscale nuclear magnetic resonance spectroscopy.