Molecular optomechanics in the anharmonic regime: from nonclassical mechanical states to mechanical lasing

TL;DR

This paper explores how molecular anharmonicities in cavity optomechanics can enable the creation of nonclassical mechanical states and control mechanical lasing, advancing the field towards more sophisticated quantum effects.

Contribution

It proposes two novel pathways leveraging molecular anharmonicities to generate nonclassical states and suppress mechanical amplification in molecular optomechanics.

Findings

Isolation of two lowest vibrational states via anharmonicity

Suppression of mechanical amplification in driven systems

Feasibility within current Surface Enhanced Raman Scattering setups

Abstract

Cavity optomechanics aims to establish optical control over vibrations of mechanical systems, to heat, cool or to drive them toward coherent, or nonclassical states. This field was recently extended to include molecular optomechanics, which describes the dynamics of THz molecular vibrations coupled to the optical fields of lossy cavities via Raman transitions, and was developed to understand the anomalous amplification of optical phonons in Surface-Enhanced Raman Scattering experiments. But the molecular platform should prove suitable for demonstrating more sophisticated optomechanical effects, including engineering of nonclassical mechanical states, or inducing coherent molecular vibrations. In this work, we propose two pathways towards implementing these effects, enabled or revealed by the strong intrinsic anharmonicities of molecular vibrations. First, to prepare a nonclassical mechanical state, we propose an incoherent analogue of the mechanical blockade, in which the molecular aharmonicity and optical response of hybrid cavities isolate the two lowest-energy vibrational states. Secondly, we show that for a strongly driven optomechanical system, the anharmonicity can effectively suppress the mechanical amplification, shifting and reshaping the onset of coherent mechanical oscillations. Our estimates indicate that both effects should be within reach of the existing implementations of the Surface Enhanced Raman Scattering, opening the pathway towards the coherent and nonclassical effects in molecular optomechanics.