Abstract
The coupling of laser light to a mechanical oscillator via radiation pressure leads to the emergence of quantum mechanical correlations between the amplitude and phase quadrature of the laser beam. These correlations form a generic non-classical resource which can be employed for quantum-enhanced force metrology, and give rise to ponderomotive squeezing in the limit of strong correlations. To date, this resource has only been observed in a handful of cryogenic cavity optomechanical experiments. Here, we demonstrate the ability to efficiently resolve optomechanical quantum correlations imprinted on an optical laser field interacting with a room temperature nanomechanical oscillator. Direct measurement of the optical field in a detuned homodyne detector ("variational measurement") at frequencies far from the resonance frequency of the oscillator reveal quantum correlations at the few percent level. We demonstrate how the absolute visibility of these correlations can be used for a quantum-enhanced estimation of the quantum back-action force acting on the oscillator, and provides for an enhancement in the relative signal-to-noise ratio for the estimation of an off-resonant external force, even at room temperature.
Highlights
The radiation pressure interaction of light with mechanical oscillators has been the subject of intense theoretical research in the gravitational wave community [1,2,3], leading, for example, to an understanding of the quantum limits of interferometric position measurements
From the perspective of the light in the interferometer, quantum fluctuations in its amplitude quadrature drive the oscillator leading to quantum backaction, and the driven motion is imprinted onto the phase quadrature
We demonstrate a room-temperature cavity-enhanced interferometer where quantum correlations of light are generated in situ via the radiation pressure interaction between light and the effective harmonic motion of the cavity
Summary
The radiation pressure interaction of light with mechanical oscillators has been the subject of intense theoretical research in the gravitational wave community [1,2,3], leading, for example, to an understanding of the quantum limits of interferometric position measurements. In recent years has this challenge been broached, by the development of cavity optomechanical systems [13], which combine an engineered high-Q, cryogenically cooled micromechanical oscillator with a high-finesse optical (or microwave) cavity In such systems, it is possible to realize a regime in which the motion of the oscillator is dominated—or nearly so—by quantum backaction [14,15,16]. This has enabled studies of various effects related to optomechanical quantum correlations, such as ponderomotive squeezing [17,18,19,20,21] and motional sideband asymmetry (using autonomous [22,23,24,25] or measurementbased [20] feedback to cool the mechanical oscillator) Accessing this regime at room temperature is difficult, as the optical powers necessary to overwhelm thermal forces with backaction are typically accompanied by dynamic instabilities [26]. We conclude by showing how quantum correlations can be used to improve the signalto-noise ratio of an off-resonant test force
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