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Optics Express

Surpassing the standard quantum limit via gain-assisted auxiliary cavities and parametric amplification

Yingjian Zhu, Xue Yan Han, Hong‐Fu Wang, Shou Zhang

Published Aug 25, 2025• 0 citations
Publisher

Abstract

The detection of weak forces plays a crucial role in various fields, from gravitational wave astronomy to biological sensing. A fundamental limitation in such measurements arises from quantum and thermal noise. Here, we present a theoretical scheme for force sensing that incorporates an optical parametric amplifier (OPA) in conjunction with a gain-assisted auxiliary cavity. We show that, in contrast to conventional lossy configurations, the presence of optical gain in the auxiliary cavity enables a substantial enhancement in sensitivity, allowing the system to exceed the standard quantum limit across a broad detection bandwidth. By carefully tuning the gain parameter, cavity-cavity coupling strength, OPA driving phase, and detuning conditions, the system achieves optimal noise suppression. Remarkably, this performance persists even under a twentyfold increase in environmental temperature, underscoring the robustness of the proposed scheme. Detailed noise analysis reveals that the contribution of the gain-assisted auxiliary cavity appears to be a negative value in the noise spectrum, effectively reducing the overall noise level of the system. This study is of significant importance to the design and fabrication of high-performance optomechanical sensors.

DOI
10.1364/oe.571212

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The detection of weak forces plays a crucial role in various fields, from gravitational wave astronomy to biological sensing. A fundamental limitation in such measurements arises from quantum and thermal noise. Here, we present a theoretical scheme for force sensing that incorporates an optical parametric amplifier (OPA) in conjunction with a gain-assisted auxiliary cavity. We show that, in contrast to conventional lossy configurations, the presence of optical gain in the auxiliary cavity enables a substantial enhancement in sensitivity, allowing the system to exceed the standard quantum limit across a broad detection bandwidth. By carefully tuning the gain parameter, cavity-cavity coupling strength, OPA driving phase, and detuning conditions, the system achieves optimal noise suppression. Remarkably, this performance persists even under a twentyfold increase in environmental temperature, underscoring the robustness of the proposed scheme. Detailed noise analysis reveals that the contribution of the gain-assisted auxiliary cavity appears to be a negative value in the noise spectrum, effectively reducing the overall noise level of the system. This study is of significant importance to the design and fabrication of high-performance optomechanical sensors.
The weak force sensing based on a coherent quantum noise cancellation (CQNC) scheme is presented in a hybrid cavity optomechanical system containing a trapped ensemble of ultracold atoms and an optical parametric amplifier (OPA). In the proposed system, the back-action noise can be completely eliminated at all frequencies and through the proper choice of the OPA parameters, and the noise spectral density can also be reduced at lower frequencies. This leads to a significant enhancement in the sensitivity of the cavity optomechanical weak force sensor, and the noise spectral density also surpasses the standard quantum limit (SQL) even for the small input power at the lower detection frequency. Furthermore, the experimental feasibility of this scheme is also briefly discussed. This study can be used for the realization of a force sensor based on hybrid cavity optomechanical systems and for the coherent quantum control in macroscopic systems.
ABSTRACT The sensitivity of optomechanical sensors is fundamentally constrained by the combined effects of shot noise and quantum back‐action. Here we show that the joint action of cross‐Kerr nonlinearity and an optical parametric amplifier (OPA) can effectively suppress these noises. By tailoring the cross‐Kerr strength, the force‐sensing sensitivity can surpass the standard quantum limit (SQL), while an optimal driving power broadens the detection bandwidth. We further find that the system becomes unstable when the detuning falls below . Importantly, the inclusion of an OPA enhances robustness against thermal fluctuations, allowing the sensitivity of force measurement to surpass the SQL even at temperatures up to 300 K. A detailed noise analysis reveals that cross‐Kerr nonlinearity predominantly suppresses back‐action noise, whereas the OPA provides a strong reduction of shot noise. These results establish a promising hybrid strategy for realizing optomechanical sensors that combine high sensitivity with thermal resilience, with broad applications ranging from medical diagnostics to gravitational‐wave astronomy.
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.
We theoretically investigate quantum measurement noise in a hybrid optomechanical system, focusing on radiation pressure back action and its impact on force sensing. The setup consists of an optomechanical cavity with a movable mirror, a fixed semi transparent mirror, an ensemble of quantum dots (QD) coupled to the cavity mode, and an intracavity optical parametric amplifier (OPA). We show how the QD induced response, together with the system nonlinearity, modifies the noise spectral density and thereby improves the force measurement sensitivity. In this setup, coherent quantum noise cancellation (CQNC) can completely remove the back action noise. In addition, increasing the OPA pump gain enables sensitivity beyond the standard quantum limit (SQL) at reduced laser power. These combined effects allow weak force sensing beyond the SQL.
We theoretically investigate quantum measurement noise in a hybrid optomechanical system, focusing on radiation-pressure back-action and its impact on force sensing. The setup consists of an optomechanical cavity with a movable mirror, a fixed semitransparent mirror, an ensemble of quantum dots (QDs) coupled to the cavity mode, and an intracavity optical parametric amplifier (OPA). We show how the QD-induced response, together with the system nonlinearity, modifies the noise spectral density and thereby improves the force measurement sensitivity. In this setup, coherent quantum noise cancellation (CQNC) can completely remove the back-action noise. In addition, increasing the OPA pump gain enables sensitivity beyond the standard quantum limit (SQL) at reduced laser power. These combined effects allow weak-force sensing beyond the SQL.
We theoretically study how quantum measurement noise can be engineered in a hybrid cavitymagnomechanical platform for precision force sensing. The proposed configuration consists of a driven optomechanical cavity, with a movable mirror on one side plus a fixed semi-transparent mirror on the other side, coupled to a magnon mode, with an OPA placed inside the cavity. We show that the magnon mediated dynamics reshapes the added-noise spectrum leading to improved sensitivity compared to a conventional optomechanical sensor. In particular, by satisfying the coherent quantum noise cancellation (CQNC) criterion, radiation-pressure back-action can be fully suppressed. In addition, a larger OPA pump gain permits operation beyond the standard quantum limit at substantially reduced laser power, thereby mitigating power-related constraints without sacrificing performance. These combined advantages provide a practical pathway to below-SQL weak force detection and can outperform existing approaches based on squeezing in magnomechanics.