Intracavity Squeezing Can Enhance Quantum-Limited Optomechanical Position Detection through Deamplification

Abstract

It has been predicted and experimentally demonstrated that by injecting squeezed light into an optomechanical device it is possible to enhance the precision of a position measurement. Here, we present a fundamentally different approach where the squeezing is created directly inside the cavity by a nonlinear medium. Counterintuitively, the enhancement of the signal to noise ratio works by de-amplifying precisely the quadrature that is sensitive to the mechanical motion without losing quantum information. This enhancement works for systems with a weak optomechanical coupling and/or strong mechanical damping. This could allow for larger mechanical bandwidth of quantum limited detectors based on optomechanical devices. Our approach can be straightforwardly extended to Quantum Non Demolition (QND) qubit detection.Recent progress in cavity optomechanics [1,2] has been so exceptional that the precision of a position measurement has been pushed until the limit set by the principles of quantum mechanics, the so-called Standard Quantum Limit (SQL) [3][4][5]. A measurement precision close to the SQL has been demonstrated in optomechanical devices with cavities both in the optical [6][7][8] and in the microwave [9] domain. Optomechanical position detection is not only of fundamental interest but finds also application in acceleration [10,11], magnetic field [12,13], and force detectors [14? ]. Thus, an important goal for the future is to develop new techniques to enhance its precision on different optomechanical platforms. Seminal efforts have focused on gravitational wave detection in optomechanical interferometers [16][17][18][19][20]. The standard route to enhance the detection precision consists in injecting squeezed light into the interferometer [16,17,21]. This technique has recently been demonstrated in the Laser Interferometer Gravitational Wave Observatory (LIGO) [22] and in a cavity optomechanics setup [23]. Externally generated squeezed light could also find application in QND qubit state detection [24,25]. Alternatively, one can enhance a dispersive quantum measurement by generating the appropriate squeezing directly inside the cavity by means of a Kerr nonlinearity [18,20,21,[26][27][28], by the dissipative optomechanical interaction [29], or potentially, by exploiting the ponderomotive squeezing [30][31][32].In this letter, we propose a new pathway to precision enhancement in optomechanical detection. In our approach, a nonlinear cavity is operated as a phase-sensitive parametric amplifier, as shown in Fig. 1. It amplifies a seed laser beam and its intensity fluctuations. Simultaneously, it de-amplifies the phase quadrature where the mechanical vibrations are imprinted. At first sight it might appear counter-intuitive that de-amplification can improve a (quantum) measurement. Here, we suggest that it might be worth to de-amplify a signal if the noise is suppressed by a larger factor thus obtaining a net enhancement of the signal to noise ratio. Indeed, our analysis shows that for optomechanical position detect...

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