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arXiv:2505.01013 · Physical Review A

Quantum backaction evasion with reservoir engineering

Yohei Nishino, James W. Gardner, Yanbei Chen, Kentaro Somiya

Published Jul 14, 2025• 2 citations
arXivHTMLPDF

Abstract

We propose a back-action evading scheme for a free mass that combines reservoir engineering with velocity measurement. The underlying principle follows the double-pass-type speed meter, which measures the mirror's velocity using a nonreciprocal interaction. In our method, the nonreciprocal coupling is realized through reservoir engineering, following the recipe proposed in [Phys. Rev. X 5, 021025]. We show that reservoir engineering can reproduce the double-pass speed meter with optimal feedforward, using only reciprocal interactions. The resulting force sensitivity surpasses the standard quantum limit, providing an alternative route to quantum back-action evasion in cavity optomechanical systems.

DOI
10.1103/bv8m-fpv9

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We propose a back-action evading scheme for a free mass that combines reservoir engineering with velocity measurement. The underlying principle follows the double-pass-type speed meter, which measures the mirror's velocity using a nonreciprocal interaction. In our method, the nonreciprocal coupling is realized through reservoir engineering, following the recipe proposed in [Phys. Rev. X 5, 021025]. We show that reservoir engineering can reproduce the double-pass speed meter with optimal feedforward, using only reciprocal interactions. The resulting force sensitivity surpasses the standard quantum limit, providing an alternative route to quantum back-action evasion in cavity optomechanical systems.
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Continuous quantum displacement measurements are fundamentally limited by a trade-off between readout imprecision and measurement back-action, constrained by the Heisenberg uncertainty principle. In the Laser Interferometric Gravitational-Wave Observatory (LIGO), these two quantum noise components dominate much of the observation band, making it an excellent testbed. We induce a sub-Hz-linewidth optomechanical mode by trapping the differential motion of the 40-kg mirrors in a band where radiation-pressure back-action dominates the motion. Engineering the quantum state entering the dark port creates correlations between imprecision and back-action that partially cancel their contributions, reducing observed motion near resonance by ~47%. A framework resolving the imprecision, back-action, and correlation terms identifies the origin of this suppression. These results demonstrate quantum back-action evasion and quantum reservoir engineering in a macroscopic optomechanical system.
Engineering a detector for sensing an extremely tiny signal such as the gravitational-wave force is a very important subject in quantum physics. A major obstacle towards this goal is that, in the standard detection scheme, the measurement noise is lower bounded by the so-called standard quantum limit (SQL), which is originated from the intrinsic measurement back-action. Hence the detector system has to be carefully engineered so that it evades the back-action and eventually beats the SQL; feedback control is, of course, expected to be a very effective method to achieve this goal. In this paper, we show that this engineering problem can be formulated and solved within the framework of well-developed geometric control theory, for a specific opto-mechanical system.
The quantum measurement of any observable naturally leads to noise added by the act of measurement. Approaches to evade or reduce this noise can lead to substantial improvements in a wide variety of sensors, from laser interferometers to precision magnetometers and more. In this paper, we develop a measurement protocol based upon pioneering work by the gravitational wave community which allows for reduction of added noise from measurement by coupling an optical field to the momentum of a small mirror. As a specific implementation, we present a continuous measurement protocol using a double-ring optomechanical cavity. We demonstrate that, with experimentally relevant parameters, this protocol can lead to significant backaction noise evasion, yielding measurement noise below the standard quantum limit over many decades of frequency.
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.
The standard quantum limit (SQL) of a classical mechanical force detection results from quantum back action perturbing evolution of a mechanical system. In this paper we show that usage of a multidimensional optical transducer may enable a broadband quantum back action evading measurement. We study theoretically a corresponding technique of measurement of a resonant signal force acting on a linear mechanical oscillator coupled to a generic optical system with three optical modes with separation nearly equal to the mechanical frequency. The measurement is performed by optical pumping of the central optical mode and analyzing the light escaping the two other modes. By detecting optimal quadrature components of the optical modes and postprocessing the measurement results we are able to exclude the back action in a broad frequency band and characterize the force with sensitivity better than the SQL. We show that the proposed scheme is similar to the multidimensional system containing quantum-mechanics-free subsystems which can evade the SQL using the idea of the so-called negative mass [M. Tsang and C. M. Caves, Phys. Rev. X 2, 031016 (2012).].