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Optics Express

Optomechanical noise suppression with the optimal squeezing process

Changwei Wang, Wei Niu, Yang Zhang, Jiong Cheng, Wen-Zhao Zhang

Published Mar 9, 2023• 4 citations
Publisher

Abstract

Quantum squeezing-assisted noise suppression is a promising field with wide applications. However, the limit of noise suppression induced by squeezing is still unknown. This paper discusses this issue by studying weak signal detection in an optomechanical system. By solving the system dynamics in the frequency domain, we analyze the output spectrum of the optical signal. The results show that the intensity of the noise depends on many factors, including the degree or direction of squeezing and the choice of the detection scheme. To measure the effectiveness of squeezing and to obtain the optimal squeezing value for a given set of parameters, we define an optimization factor. With the help of this definition, we find the optimal noise suppression scheme, which can only be achieved when the detection direction exactly matches the squeezing direction. The latter is not easy to adjust as it is susceptible to changes in dynamic evolution and sensitive to parameters. In addition, we find that the additional noise reaches a minimum when the cavity (mechanical) dissipation κ(γ) satisfies the relation κ = Nγ, which can be understood as the restrictive relationship between the two dissipation channels induced by the uncertainty relation. Furthermore, by taking into account the noise source of our system, we can realize high-level noise suppression without reducing the input signal, which means that the signal-to-noise ratio can be further improved.

DOI
10.1364/oe.477710

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Quantum squeezing-assisted noise suppression is a promising field with wide applications. However, the limit of noise suppression induced by squeezing is still unknown. This paper discusses this issue by studying weak signal detection in an optomechanical system. By solving the system dynamics in the frequency domain, we analyze the output spectrum of the optical signal. The results show that the intensity of the noise depends on many factors, including the degree or direction of squeezing and the choice of the detection scheme. To measure the effectiveness of squeezing and to obtain the optimal squeezing value for a given set of parameters, we define an optimization factor. With the help of this definition, we find the optimal noise suppression scheme, which can only be achieved when the detection direction exactly matches the squeezing direction. The latter is not easy to adjust as it is susceptible to changes in dynamic evolution and sensitive to parameters. In addition, we find that the additional noise reaches a minimum when the cavity (mechanical) dissipation κ(γ) satisfies the relation κ = Nγ, which can be understood as the restrictive relationship between the two dissipation channels induced by the uncertainty relation. Furthermore, by taking into account the noise source of our system, we can realize high-level noise suppression without reducing the input signal, which means that the signal-to-noise ratio can be further improved.
A coherent feedback scheme is used to enhance the degree of squeezing of the output field in a cavity optomechanical system. In the feedback loop, a beam splitter (BS) plays the roles of both a feedback controller and an input-output port. To realize effective enhancement, the output quadrature should take the same form as the input quadrature, and the system should operate at the deamplification situation in the meantime. This can be realized by choosing an appropriate frequency-dependent phase angle for the generalized quadrature. Additionally, both the transmissivity of the BS and the phase factor induced by time delays in the loop affect optical squeezing. For the fixed frequency, the optimal values of transmissivity and phase factor can be used to achieve the enhanced optical squeezing. The effect of optical losses on squeezing is also discussed. Optical squeezing is degraded by the introduced vacuum noise owing to the inefficient transmission in the loop. We show that the enhancement of squeezing is achievable with the parameters of the current experiments.
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.
Abstract A scheme of backaction evading and amplification of weak force signal is presented in an optomechanical system. By introducing the frequency modulation of the cavity field, the system can achieve the quantum nondemolition measurement interaction so that the backaction evading can be reached. With the help of the mechanical squeezing, the weak force signal can be amplified, which equals to amplifying the mechanical response function, reducing additional noise as well as thermal noise of mechanical oscillator. The current scheme opens up an alternative method for simultaneously surpassing the standard quantum limit and enhancing the mechanical response, and also reducing the mechanical thermal noise.
This research focuses on advanced noise suppression technologies for high-precision measurement systems, particularly addressing the limitations of classical noise reducing approaches. The noise level of laser sources is a crucial factor that directly affects the measurement sensitivity in applications such as gravitational wave detection and biomedical imaging. Classical feedback control technologies are effective but often encounter a bottleneck resulting from the classical noise suppression limits. To cope with these challenges, a novel method integrating quantum squeezed light with classical feedback control systems to reduce intensity noise is proposed in this work. By employing an amplitude-squeezed light field, a quantum-enhanced feedback control model is developed, thereby theoretically examining the influence of both the feedback loop gain and the degree of squeezing on the noise suppression performance. The results show that the injection of squeezed light significantly reduces the intensity noise, approaching the shot noise limit (SNL), thereby improving the system sensitivity beyond the classical noise reduction boundaries. Specifically, –10 dB squeezed state injection into the feedback system yields an additional noise suppression of approximately 8.97 dB, exceeding what is achievable using classical feedback alone. This demonstrates that the potential of the proposed method can enhance measurement precision close to the quantum noise limits without increasing the laser power. The analysis highlights the asymmetric noise suppression effects between the inner feedback loop and outer feedback loop. Although the outer loop benefits significantly from the squeezed light injection and achieves noise levels that are unattainable by classical feedback methods, the inner loop shows relatively minor improvements. This asymmetry is attributed to the inherent characteristics of quantum squeezing and the limitations of the feedback loop design. Further investigation into the individual noise components reveals that the primary contributors to the intensity noise include input noise, photodetector noise, and beam splitter-induced vacuum fluctuations. The injection of squeezed light effectively mitigates these vacuum fluctuations, which are typically a major noise source in high-precision laser systems. Theoretical research results show that the use of squeezed light in feedback control systems can effectively enhance noise suppression, equivalent to a nine fold increase in detected optical power, without the physical drawbacks of increasing laser power such as thermal noise. In conclusion, this study provides a theoretical validation of combining quantum squeezed states with classical feedback control to exceed classical noise suppression limits. The integration of a –10 dB squeezed state demonstrates a significant noise reduction, showing that this hybrid approach could revolutionize noise management in precision measurement applications. The results pave the way for further exploring quantum-enhanced control technologies in fields such as gravitational wave detection, quantum communication, and advanced optical sensing, providing a pathway for improving sensitivity and noise suppression without increasing additional power requirements.
A theoretical scheme is proposed to enhance the signal-to-noise ratio in ultrasensitive detection by quantum correlation in a composite optomechanical system. Introducing an auxiliary oscillator and treating it as an added probe for weak-field detection, the additional noise can be greatly suppressed, which may even break the standard quantum limit. A magnetic field is employed as an example to exhibit the detection capability of the scheme. The result shows that, compared with the traditional detection protocol, the scheme has a higher signal-to-noise ratio and a better detection accuracy. Furthermore, the signal intensity detection curve shows a good linearity. The results provide a promising platform for reducing the additional noise by utilizing quantum correlation in ultrasensitive detection.
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.