Abstract An experimentally feasible magnetometer based on a dual‐coupling optomechanical system is proposed, where the radiation‐pressure coupling transduces the magnetic signal to the optical phase, and the quadratic optomechanical interaction induces a periodic squeezing effect. The latter not only amplifies the signal to be measured, but also accelerates the signal transducing rate characterized by an experimentally observable phase accumulation efficiency. In the vicinity of opto‐mechanical decoupled time, the ultimate bound to the estimability of magnetic signal is proportional to , and then the optimized accuracy of estimation can be enhanced nearly three orders with a controllable squeezing parameter . Moreover, this proposal is robust against the mechanical thermal noise, and the sensitivity of a specific measurement can reach to the order of in the presence of dissipations and without ground state cooling of mechanical oscillator. The proposal fundamentally broadens the fields of quantum metrology and cavity optomechanics, with the potential application for on‐chip magnetic detection with high precision.
Abstract An experimentally feasible magnetometer based on a dual‐coupling optomechanical system is proposed, where the radiation‐pressure coupling transduces the magnetic signal to the optical phase, and the quadratic optomechanical interaction induces a periodic squeezing effect. The latter not only amplifies the signal to be measured, but also accelerates the signal transducing rate characterized by an experimentally observable phase accumulation efficiency. In the vicinity of opto‐mechanical decoupled time, the ultimate bound to the estimability of magnetic signal is proportional to , and then the optimized accuracy of estimation can be enhanced nearly three orders with a controllable squeezing parameter . Moreover, this proposal is robust against the mechanical thermal noise, and the sensitivity of a specific measurement can reach to the order of in the presence of dissipations and without ground state cooling of mechanical oscillator. The proposal fundamentally broadens the fields of quantum metrology and cavity optomechanics, with the potential application for on‐chip magnetic detection with high precision.
Standard optomechanical sensors operating in the low-temperature regime often face fundamental precision limits imposed by vacuum fluctuations. Here, we demonstrate that moving beyond conventional radiation-pressure interactions and exploiting quadratic coupling can surpass these limits, generating intrinsic squeezing and non-Gaussian features in the probe state. We study quantum thermometry and magnetometry in a coupled two-resonator system, focusing on estimating the temperature of a thermal bath and an external magnetic field. The resonators are assumed to be in thermal equilibrium with a common bath, while a weak magnetic field acts on one of the resonators. We perform measurements on a single resonator, which serves as the probe to estimate both parameters. We compute the quantum Fisher information of the probe for two different interaction models between the resonators. Our results show that the counter-rotating terms in the quadratic interaction naturally induce squeezing at intermediate coupling and strong non-Gaussian correlations as the coupling increases further. These effects yield orders-of-magnitude enhancement in sensitivity in the low-temperature and weak-field regimes compared to standard radiation-pressure couplings. Finally, we investigate multiparameter estimation and find that, although the optimal measurements remain compatible, statistical correlations between parameters prevent the simultaneous estimation of temperature and magnetic field from attaining single-parameter precision.
Cavity optomechanics originated from the research of interferometric detection of gravitational waves, and later became a fast-growing area of techniques and approaches ranging from the fields of atomic, molecular, and optical physics to nano-science and condensed matter physics as well. Recently, it focused on the exploration of operating mechanical oscillators deep in the quantum regime, with an interest ranging from quantum-classical interface tests to high-precision quantum metrology. In this paper, recent theoretical work of our group in the field of quantum measurement with cavity optomechanical systems is reviewed. We explore the quantum measurement theory and its applications with several unconventional cavity optomechanical schemes working in the quantum regime. This review covers the basics of quantum noises in the cavity optomechanical setups and the resulting standard quantum limit of precision displacement and force measurement. Three novel quantum measurement proposals based on the hybrid optomechanical system are introduced. First, we describe a quantum back-action insulated weak force sensor. It is realized by forming a quantum-mechanics-free subsystem with two optomechanical oscillators of reversed effective mass. Then we introduce a role-reversed atomic optomechanical system which enables the preparation and the quantum tomography of a variety of non-classical states of atoms. In this system, the cavity field acts as a mechanical oscillator driven by the radiation pressure force from an ultracold atomic field. In the end, we recommend a multimode optomechanical transducer that can detect intensities significantly below the single-photon level via adiabatic transfer of the microwave signal to the optical frequency domain. These proposals demonstrate the possible applications of optomechanical devices in understanding of quantum-classical crossover and in achieving quantum measurement limit.
Cavity optomechanical (COM) sensors, enhanced by quantum squeezing or entanglement, have become powerful tools for measuring ultra-weak forces with high precision and sensitivity. However, these sensors usually rely on linear COM couplings, a fundamental limitation when measurements of the mechanical energy are desired. Very recently, a giant enhancement of the signal-to-noise ratio was predicted in a quadratic COM system. Here we show that the performance of such a system can be further improved surpassing the standard quantum limit by using quantum squeezed light. Our approach is compatible with available engineering techniques of advanced COM sensors and provides new opportunities for using COM sensors in tests of fundamental laws of physics and quantum metrology applications.
We study the fundamental sensitivity that can be achieved with an ideal optomechanical system in the nonlinear regime for measurements of time-dependent gravitational fields. The optomechanical system consists of a cavity mode and a mechanical oscillator coupled to it via (non-linear) radiation pressure coupling. Using recently developed methods to solve the dynamics of a nonlinear optomechanical system with a time-dependent Hamiltonian, we compute the quantum Fisher information for linear displacements of the mechanical element due to gravity. We demonstrate that the sensitivity can be further enhanced by injecting squeezed states of the cavity field or by modulating the light–matter coupling of the optomechanical system. We specifically apply our results to the measurement of gravitational fields from small oscillating masses, where we show that, in principle, the gravitational field of an oscillating nanogram mass can be detected based on experimental parameters that will likely be accessible in the near-term future. Finally, we identify the experimental parameter regime necessary for gravitational wave detection with a quantum optomechanical sensor.
ABSTRACT In this paper, we investigate how to achieve strong optomechanical entanglement and mechanical squeezing in a membrane‐embedded cavity optomechanical system incorporating a coherent feedback loop, where the membrane interacts with the cavity mode through both linear and quadratic optomechanical couplings. This hybrid optomechanical architecture offers a flexible tunability of intrinsic system parameters, thereby enabling controlled stiffening or softening of the mechanical mode through adjusting quadratic optomechanical coupling, as well as effective modulation of the cavity decay rate via feedback control. More importantly, the synergistic interplay effect allows for a strategic reconfiguration of the system's stability regime, which in turn permits the presence of significantly enhanced effective optomechanical coupling strengths before entering the unstable regime. Exploiting these unique features, we showcase that optomechanical entanglement can be substantially enhanced with positive coupling sign and suitable feedback parameters, while strong mechanical squeezing beyond the 3dB limit is simultaneously achieved over a broad parameter range with negative coupling sign, reaching squeezing degree above 10dB under optimized conditions. Our proposal, establishing an all‐optical method for generating highly entangled or squeezed states in cavity optomechanical systems, opens up a new route to explore macroscopic quantum effects and to advance quantum information processing.
Quantum sensing, leveraging the principles of quantum mechanics, has revolutionized the field of precision measurement by achieving sensitivities beyond the classical limits. Among the various platforms for quantum sensing, cavity optomechanics has emerged as a particularly promising field. It studies the interaction between light and mechanical resonators within high-Q optical cavities, providing unique opportunities for enhancing measurement precision and sensitivity in quantum sensing. With advancements in technology, the range of applications for cavity optomechanics in quantum sensing is expanding rapidly. Particularly, the integration of optoelectronic technologies and miniaturization techniques holds promise for the development of more compact, efficient, and scalable quantum sensors. Quantum sensing with cavity optomechanics has been extensively studied and has progressed enormously over the past decades. This paper provides a systematic review of research on quantum sensing with cavity optomechanics, starting from the fundamental principles of optomechanical coupling, to the achievement of quantum ground-state cooling of mechanical oscillators and the preparation of basic quantum states, and then to the mechanisms of quantum sensing based on cavity optomechanics. Furthermore, we survey recent advancements in quantum sensing utilizing cavity optomechanics, including the enhancement of optomechanical sensing through the use of entanglement, squeezing, and quantum exceptional points. Finally, perspectives and opportunities for future developments of this field are provided.