Tunable anharmonicity in cavity optomechanics in the unresolved sideband regime

TL;DR

This paper presents a theoretical study of how to induce and control anharmonicity in mechanical oscillators within cavity optomechanics, especially in the unresolved sideband regime, revealing signatures in the displacement spectrum and light field.

Contribution

It introduces a method to tune anharmonicity in mechanical systems via ponderomotive coupling in the unresolved sideband regime, with analytical and numerical predictions of observable signatures.

Findings

Mechanical displacement spectrum shows signatures of anharmonicity.

Tuning system parameters can lead to a purely quartic potential.

Mechanical state can be highly non-Gaussian despite high-temperature thermalization.

Abstract

Introducing a controlled and strong anharmonicity in mechanical systems is a present challenge of nanomechanics. In cavity optomechanics a mechanical oscillator may be made anharmonic by ponderomotively coupling its motion to the light field of a laser-driven cavity. In the regime where the mechanical resonating frequency and the single-photon coupling constant are small compared to the decay rate of the cavity field, it turns out that the quantum electromagnetic fluctuations of the laser field drive the oscillator into a high-temperature thermal state. The motional state may however be highly non-Gaussian; we show that a precise tuning of system parameters may even lead to a purely quartic effective potential for the mechanical oscillator. We present a theory that predicts the measurable signatures left by the mechanical anharmonicity. In particular, we obtain analytically and numerically the mechanical displacement spectrum, and explore the imprints of the mechanical anharmonicity on the cavity light field.