Quantum sensing has a bright future for applications in need of impeccable sensitivities. The study of periodic fields has resulted in various techniques, which deal with the limited coherence time of the quantum sensor in several ways. However, the periodic signal to measure could include forms of randomness as well, such as changes in phase or in frequency. In such cases, long measurement times required to detect the smallest of field amplitudes hamper the effectiveness of conventional techniques. In this paper, we propose and explore a robust sensing technique to combat this problem. For the technique, instead of measuring the signal amplitude directly, we measure another global property of the signal, in this case the standard deviation. This results in a much-improved sensitivity. We analyze the advantages and limitations of this technique, and we demonstrate the working with a measurement using a nitrogen-vacancy center. This work encourages scouting measurements of alternative statistics.
Quantum sensing has a bright future for applications in need of impeccable sensitivities. The study of periodic fields has resulted in various techniques, which deal with the limited coherence time of the quantum sensor in several ways. However, the periodic signal to measure could include forms of randomness as well, such as changes in phase or in frequency. In such cases, long measurement times required to detect the smallest of field amplitudes hamper the effectiveness of conventional techniques. In this paper, we propose and explore a robust sensing technique to combat this problem. For the technique, instead of measuring the signal amplitude directly, we measure another global property of the signal, in this case the standard deviation. This results in a much-improved sensitivity. We analyze the advantages and limitations of this technique, and we demonstrate the working with a measurement using a nitrogen-vacancy center. This work encourages scouting measurements of alternative statistics.
Quantum sensing aims to detect signals with unparalleled sensitivity, potentially surpassing classical limitations. Solid-state spin defects, particularly nitrogen-vacancy centers in diamond, have emerged as promising platforms due to their long coherence time, optical addressability, high field sensitivity, and spatial and spectral resolution, making them ideal for sensing and imaging applications. Their compact size and robust performance under room temperature and ambient conditions further enhance their suitability for real-world applications. We provide an overview of quantum sensing principles and explore efforts to improve sensor functionality, including advanced sensing protocols, spatial imaging techniques, and integration with optical systems to enhance detection efficiency. We also highlight recent progress in the applications of these sensors across various use cases, including biomedical diagnostics, semiconductor device inspection, and industrial and military applications.
The sensing of external fields using quantum systems is a prime example of an emergent quantum technology. Generically, the sensitivity of a quantum sensor consisting of N independent particles is proportional to sqrt[N]. However, interactions invariably occurring at high densities lead to a breakdown of the assumption of independence between the particles, posing a severe challenge for quantum sensors operating at the nanoscale. Here, we show that interactions in quantum sensors can be transformed from a nuisance into an advantage when strong interactions trigger a dissipative phase transition in an open quantum system. We demonstrate this behavior by analyzing dissipative quantum sensors based upon nitrogen-vacancy defect centers in diamond. Using both a variational method and a numerical simulation of the master equation describing the open quantum many-body system, we establish the existence of a dissipative first order transition that can be used for quantum sensing. We investigate the properties of this phase transition for two- and three-dimensional setups, demonstrating that the transition can be observed using current experimental technology. Finally, we show that quantum sensors based on dissipative phase transitions are particularly robust against imperfections such as disorder or decoherence, with the sensitivity of the sensor not being limited by the T_{2} coherence time of the device. Our results can readily be applied to other applications in quantum sensing and quantum metrology where interactions are currently a limiting factor.
Nitrogen—Vacancy (NV) center in diamond can detect tiny magnetic field due to relative long coherence time even at room temperature. Its optical accessibility and capability of thin-film formation provide us an interesting sensing modality such as wide field imaging. We have reported phase sensitive protocol for ac magnetic field designed for wide field setup.[1] In this study we demonstrate an application of phase sensitive protocol; measuring distribution of ac magnetic field strength by phase sensing. Previous methods of multi-pulse quantum sensing such as XY8 realize quite high sensitivity of ac magnetic field. Since XY8 has dependencies on strength and phase of ac magnetic field, it is necessary to adjust ac phase to an optimal point in order to obtain a best sensitivity, and we cannot distinguish the effect of amplitude and phase. Recent studies have showed utilizing time-domain information is effective for improving frequency resolution of quantum sensing,[2,3] and we found same technique is also effective for simultaneous measurement of strength and phase. Here we propose a robust method for amplitude estimation by phase sensing. We added another signal for reference, then sensing phase difference between target signal and reference can be converted into amplitude. Conventional XY8 sensing is based upon fluorescence measurement which can be affected easily by many obstacles such as stray light, autofluorescence, and fringes of excitation laser. In the other hand, our method can be more robust because it is based on phase measurement. Nothing can change the phase except absorption of ac signal. This work was supported by MEXT Q-LEAP, CAO PRISM, Japan. [1] Mizuno et al., AIP advances 2018 [2][3] Boss, Schmitt
Magnetic spectroscopy at the nanoscale provides unique insights into material properties and dynamics, with quantum sensors like nitrogen-vacancy (NV) centers being ideally suited for these scales. However, detecting low-frequency signals remains a challenge due to finite coherence times (T2∗), as signals oscillating slower than 1/T2∗ decay before sufficient phase accumulation occurs. We present RESOLUTE (Ramsey corrElation SpectroscOpy puLse seqUence wiTh phasE cycling), a protocol that overcomes these limitations by combining Ramsey measurements with correlation spectroscopy. By storing accumulated phase as a population imbalance during a correlation period (Tcorr<T1) between two sensing periods, RESOLUTE generates an effective coherence time T2p>T2∗. This shifts the frequency-matching condition to the correlation time, enabling detection in the previously inaccessible spectral region between 1/T1 and 1/T2p. We experimentally demonstrate an extension of the effective coherence time from T2∗=0.38μs to T2p=5.1μs, surpassing Hahn Echo measurements. The technique successfully detects 13C nuclear spin Larmor precession at fields as low as 49G ($\sim50\,$kHz). We further provide theoretical insight using Fisher information to characterize RESOLUTE's frequency estimation capabilities compared to existing protocols. Finally, by integrating adiabatic pulses and phase cycling, we demonstrate robust spin control and effective DC signal extraction. These advancements provide enhanced sensitivity to weak dipolar interactions, essential for single-molecule imaging and quantum sensing applications.
Quantum sensors hold great promise for achieving better sensitivity in the measurement of physical quantities compared to their classical counterparts. However, the conditions under which quantum advantage in sensing can be achieved are rather restrictive, and most quantum enhancements in sensing are lost in the presence of noise, errors, or a poorly calibrated system. To overcome these limitations, we are motivated to import ideas from fault-tolerant quantum computing to quantum sensing. Specifically, we consider a qubit noise model where the probability of phase-flip errors is exponentially smaller (in qubit number) compared to the probability of bit-flip errors that occur with probability p. For this noise structure, we demonstrate that, given a total sensing time T, Heisenberg scaling can be attained for times up to T∝1/p(N+1)/2 for a N-qubit repetition code, in contrast with T∝1/p without using a fault-tolerant sensing protocol.
This paper proposes a novel approach to quantum sensing that fundamentally shifts the perspective on quantum noise. Instead of viewing it as an unwanted disturbance, we argue that quantum noise is a critical resource for extracting subtle environmental information. The core concept involves designing a quantum sensor that leverages the statistical properties of quantum noise to precisely measure and interpret its distribution, ultimately enabling the detection of extremely weak signals. This approach moves beyond traditional quantum sensing methodologies which often rely on minimizing noise. We present a theoretical framework and mathematical formalism for this concept, outlining the principles of operation and potential performance characteristics. The underlying mechanism hinges on the ability to correlate the statistical fluctuations of quantum noise with the underlying environmental signal. This work represents a significant departure from conventional thinking and offers a new paradigm for quantum sensing technology. ---