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arXiv:2003.12524 · Physical Review A

Efficient detection of inhomogeneous magnetic fields from a single spin with Dicke states

Hideaki Hakoshima, Yuichiro Matsuzaki

Published Oct 20, 2020• 14 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1103/physreva.102.042610

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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 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.
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.
Quantum sensing has become a key technology for precision measurement, with applications spanning magnetometry, gravitational sensing, navigation and geodesy, materials and device diagnostics, and biomedical detection. This motivates the study of quantum-enhanced magnetometry with entangled states. We focus on Greenberger–Horne–Zeilinger (GHZ) and Dicke states operated within a Kitaev phase estimation algorithm (PEA). We consider superconducting fluxonium-qubit sensors, which are modelled with relaxation and dephasing noise. Using a Bayesian update procedure, we evaluate the estimation performance and compare the GHZ and Dicke sensors in terms of sensitivity, dynamical range, and information gain. GHZ probes achieve the highest local sensitivity, while Dicke probes maintain comparable sensitivity over a substantially wider bias interval and exhibit improved tolerance to bias errors and edge effects in PEA sequence. Our results demonstrate a trade-off between local peak sensitivity and the achievable dynamical range and robustness under noise.
Entanglement is an essential resource in many quantum information tasks and the entanglement witness is a widely used tool for its detection. In experiments the prepared state generally deviates from the target state due to some noise. Normally the white-noise model is applied to quantifying such a derivation and at the same time reveals the robustness of the witness. However, there may exist other kinds of noise, in which the coherent noise can dramatically ``rotate'' the prepared state. In this way, coherent noise is likely to lead to a failure of detection, even though the underlying state is actually entangled. In this work, we propose an efficient entanglement detection protocol for NNN-partite Greenberger-Horne-Zeilinger (GHZ)--like states. The protocol can eliminate the effect of coherent noise and at the same time feedback the corresponding noise parameters, which are beneficial to further improvements of the experiment system. In particular, we consider two experiment-relevant coherent noise models; one is from the unconscious phase accumulation on NNN qubits, and the other is from the rotation on the control qubit. The protocol effectively realizes a family of entanglement witnesses by postprocessing the measurement results from N+2N+2N+2 local measurement settings, which adds only one more setting than the original witness specialized for the GHZ state. Moreover, by considering the trade-off between the detection efficiency and the white-noise robustness, we further reduce the number of local measurements to three without altering the performance under the coherent noise. Our protocol can enhance entanglement detection under coherent noises and act as a benchmark for state-of-the-art quantum devices.
Greenberger-Horne-Zeilinger (GHZ) state is a typical maximally entangled state which is pursued in both fundamental research and emerging quantum technologies. Preparing large-scale GHZ states in lattice spin systems is particularly appealing for quantum advantages, but conventional schemes face great challenges in scalability. Here we propose a universal and scalable scheme to generate large-scale GHZ-like states, which share similar entanglement and metrological properties with standard GHZ states, in lattice spin systems through global Floquet engineering. Our scheme requires only global operations and shows great advantage for large particle number. It is applicable to systems with arbitrary interaction ranges, offering a practical pathway for large-scale implementation of many-body entangled states in various systems.
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.