Cavity optomechanics in a levitated helium drop

Abstract

We describe a proposal for a type of optomechanical system based on a drop of liquid helium that is magnetically levitated in vacuum. In the proposed device, the drop would serve three roles: its optical whispering-gallery modes would provide the optical cavity, its surface vibrations would constitute the mechanical element, and evaporation of He atoms from its surface would provide continuous refrigeration. We analyze the feasibility of such a system in light of previous experimental demonstrations of its essential components: magnetic levitation of mm-scale and cm-scale drops of liquid He, evaporative cooling of He droplets in vacuum, and coupling to high-quality optical whispering-gallery modes in a wide range of liquids. We find that the combination of these features could result in a device that approaches the single-photon strong-coupling regime, due to the high optical quality factors attainable at low temperatures. Moreover, the system offers a unique opportunity to use optical techniques to study the motion of a superfluid that is freely levitating in vacuum (in the case of 4 He). Alternatively, for a normal fluid drop of 3 He, we propose to exploit the coupling between the drop's rotations and vibrations to perform quantum nondemolition measurements of angular momentum.

Beyond linear coupling in microwave optomechanics

“…Beyond the standard optical frequency pulling proportional to mechanical position x, higher-order couplings appear to also be significant or even desirable for specific realizations: From an x 2 coupling, one can measure the energy of the mechanics and build quantum nondemolition (QND) measurements [26,27], i.e., measuring an eigenstate of the Hamiltonian while not perturbing its evolution. Successful experimental implementations of such nonlinear couplings have been realized using optics with membrane-in-the-middle configurations [28] and superfluid optomechanics [29]. On a more fundamental level, experiments which seek to use optomechanical systems to probe gravity's quantum signatures, a completely new frontier of physics [30,31], require necessarily to have characterized the higher order (beyond linear) mechanical couplings in the optomechanical Hamiltonian [32].…”

Encoding a qubit in a molecule

“…Though we have emphasized the potential applications to atoms and molecules, the same ideas can be applied to any quantized 3-dimensional rigid body that can be coherently manipulated. While there is a size limitation due to decoherence, we are on the cusp of entering the quantum regime for levitated nanoscale particles of helium [118], vaterite [119], diamond (alone [120] or doped [121]), and silicon [122][123][124], to name a few. Nanoparticles may seem to be unlikely candidates for quantum computing, but it would be interesting nonetheless to try to stabilize quantum superpositions of their orientational states (cf.…”

Decoherence of nonrelativistic bosonic quantum fields

“…Quantum systems with a large number of interacting constituents can often be effectively described in terms of quantum fields. Examples include degenerate quantum gases and fluids [1,2], collective degrees of freedom in strongly correlated solid-state systems [3,4], acoustic vibrations in superfluid helium [5][6][7], micromechanical oscillators [8,9], and closely spaced chains of harmonic oscillators realized, for example, in ion traps [10] and superconducting circuits [11]. For such many-body systems a minimal and generic field-theoretic model that appropriately accounts for the decoherence dynamics toward a corresponding classical field theory is desirable.…”