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arXiv:2207.09261 · Physical Review A

Enhancing the sensitivity of nonlinearity sensors through homodyne detection in dissipatively coupled systems

Dianzhen Cui, Jianning Li, Fude Li, Zhi‐Cheng Shi, X. X. Yi

Published Jan 17, 2023• 12 citations
arXivHTMLPDF

Abstract

In this paper, we propose a sensing mechanism to enhance the sensitivity of a quantum system to nonlinearities by homodyning the amplitude quadrature of the cavity field. The system consists of two dissipatively coupled cavity modes, one of which is subject to single- and two-photon drives. In the regime of low two-photon driving strength, the spectrum of the system acquires a real spectral singularity. We find that this singularity is very sensitive to the two-photon drive and nonlinearity of the system, and compared to the previous nonlinearity sensor, the proposed sensor achieves an unprecedented sensitivity around the singularity point. Moreover, the scheme is robust against fabrication imperfections. This work would open a different avenue for quantum sensors, which could find applications in many fields, such as precise measurement and quantum metrology.

DOI
10.1103/physreva.107.013709

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In this paper, we propose a sensing mechanism to enhance the sensitivity of a quantum system to nonlinearities by homodyning the amplitude quadrature of the cavity field. The system consists of two dissipatively coupled cavity modes, one of which is subject to single- and two-photon drives. In the regime of low two-photon driving strength, the spectrum of the system acquires a real spectral singularity. We find that this singularity is very sensitive to the two-photon drive and nonlinearity of the system, and compared to the previous nonlinearity sensor, the proposed sensor achieves an unprecedented sensitivity around the singularity point. Moreover, the scheme is robust against fabrication imperfections. This work would open a different avenue for quantum sensors, which could find applications in many fields, such as precise measurement and quantum metrology.
Cavity optomechanical systems have emerged as a promising platform for quantum sensing. Quantum mechanics imposes a standard quantum limit (SQL) on the force-sensitivity for the standard homodyne phase quadrature measurement of the cavity's output field. In this paper, we investigate ways to enhance weak force sensitivity beyond SQL by employing a variational homodyne quadrature readout and quantum squeezing. Our study reveals a remarkable improvement in the force sensitivity of a cavity optomechanical sensor at a suitable homodyne angle, compared with standard phase quadrature detection of the cavity output field within a specific frequency band. We further demonstrate improved force sensitivity via intra-cavity squeezing (ICS) or injected external squeezing (IES) of the cavity mode. Both variational homodyne readout and quantum squeezing induce quantum correlations between the amplitude and phase quadratures of the cavity's output field, thereby improving force sensitivity. Our results suggest that IES is preferable to ICS for sub-SQL force sensing with system stability and lower probe power requirements. The squeezing-enhanced variational homodyne detection scheme can enable high-precision quantum sensing across various hybrid quantum platforms.
The study of force sensitivity based on a cavity optomechanical system plays a prominent role in quantum precision measurement and provides an ideal platform for precision sensing technology. Here, we propose a scheme to enhance the force sensitivity of a dissipatively coupled optomechanical system by inducing Duffing nonlinearity. The numerical analysis shows that inducing Duffing nonlinearity significantly improves the force sensitivity compared to the system without Duffing nonlinearity, even surpassing the standard quantum limit (SQL) by more than five orders of magnitude. Moreover, we demonstrated that the sensitivity of force sensing is robust to temperature when Duffing nonlinearity is induced. More interestingly, the induction of Duffing nonlinearity broadens the detection bandwidth. At the same time, the detection frequency below the SQL also experiences a significant frequency shift with changes in the nonlinear amplitude. Our scheme not only holds potential for applications in quantum manipulation but also realizes macroscopic quantum effects.
Recent progress has revealed that quantum systems with multiple position-dependent couplings, e.g., giant atoms, can exhibit some unconventional phenomena, such as non-exponential decay. However, their potential applications are still open questions. In this paper, we propose a giant-cavity-based quantum sensor for the first time, whose performance can be greatly enhanced compared to traditional cavity-based sensors. In our proposal, two cavities are coupled to a dissipative reservoir at multiple points while they couple to a gain reservoir in a single-point way. To detect an unknown parameter entering the sensor, a waveguide is coupled to one of the cavities where detecting fields can pass through for homodyne detection. We find that multiple position-dependent couplings can induce an inherent non-reciprocal coupling between the cavities, which can enhance the performance of sensors. Compared to the results in the work of Lau and Clerk, (Nat Commun, 2018, 9: 4,320), our output noise can remain at the shot noise level, which is about one order of magnitude lower. In addition, the signal-to-noise ratio per photon is also enhanced by about one order of magnitude. These results showed that the multiple-point coupling structure is beneficial to existing quantum devices.
The precise measurement of weak optomechanical coupling is fundamentally limited by the inevitable thermal noise and the stringent parameter control. To overcome these limitations, we propose what we feel is a novel sensing scheme based on self-Kerr nonlinearity. Remarkably, the self-Kerr nonlinearity induced by the Born-Oppenheimer (BO) adiabatic separation between the optical and mechanical modes enables a sensitivity scaling law proportional to g −7/3 , which is the source of extraordinary sensitivity to weak optomechanical coupling. By developing an effective indirectly coupled dual-cavity model featuring self-Kerr nonlinearity and applying Gaussian quantum information theory, we demonstrate that a weak optomechanical coupling can be detected with both an excellent signal-to-noise ratio (SNR) and high precision. Specifically, our scheme improves the SNR and precision by several orders of magnitude, surpassing the capabilities of conventional nonlinear response methods. This work elucidates a fundamental mechanism based on self-Kerr nonlinearity for achieving ultra-high sensitivity in non-Hermitian sensors, thereby paving the way for the development of high-performance sensors in anharmonic systems and advancing the field of ultrasensitive quantum metrology.
Abstract A theoretical scheme is proposed to enhance the sensitivity of force sensors with quantum non-demolition measurement (QND) in an optomechanical setup assisted by four-tone optical driving and an optical parametric amplifier (OPA). With the help of special drive, the system can be simplified as the typical type of QND for force sensing, so that the backaction noise can be evaded to surpass the standard quantum limit. Besides, the added noise can be suppressed owing to the modified optical susceptibility resulting from the OPA. By introducing two oscillators coupling with two charged bodies respectively, the signal can be enhanced with the nonlinearity caused by Coulomb interaction, while the noise presents an exponential decrease. Moreover, considering the homodyne detection effect, the range of system parameters and frequency bands will be broadened. The present investigation may provide a route toward simultaneously evading backaction noise, reducing the mechanical thermal noise, and enhancing the external signal, which can be an alternative design for sensitive devices.
The challenge of developing high-precision temperature sensors is an important issue that has recently received a lot of attention. In this work, we introduce an estimation technique to precisely measure the temperature of a quantum reservoir using a Kerr-nonlinear resonator with drive. Thermalization in our suggested protocol is assessed using Uhlmann-Jozsa fidelity, then we utilize quantum Fisher information to evaluate the metrological potential of our thermometery scheme. We observe that increasing the Kerr-nonlinearity coefficient and driving amplitude significantly enhances precision in the temperature estimation. Furthermore, we also explore the underlying physical mechanisms by analyzing probe purity in the steady state and evaluating the performance of homodyne versus heterodyne detection methods. Our results demonstrate that neither of these Gaussian measurements is optimal; instead, optimal homodyne detection always surpasses heterodyne detection.