Phonon Pumping by Modulating the Ultrastrong Vacuum

TL;DR

This paper proposes a method to generate real mechanical excitations from the virtual photons in the ground state of an ultrastrong light-matter coupled system, enabling observation of phonon pumping driven by virtual particles.

Contribution

It introduces a protocol for phonon generation via modulating a two-level system in an ultrastrong coupling regime, linking virtual photon populations to observable mechanical excitations.

Findings

Real phonons are emitted when modulating the two-level system at the mechanical resonator's frequency.

The effect is directly related to the virtual photon population in the ground state.

A feasible superconducting-optomechanical setup is proposed for experimental observation.

Abstract

The vacuum (i.e., the ground state) of a system in ultrastrong light-matter coupling contains particles that cannot be emitted without any dynamical perturbation and is thus called virtual. We propose a protocol for inducing and observing real mechanical excitations of a mirror enabled by the virtual photons in the ground state of a tripartite system, where a resonant optical cavity is ultrastrongly coupled to a two-level system (qubit) and, at the same time, optomechanically coupled to a mechanical resonator. Real phonons are coherently emitted when the frequency of the two-level system is modulated at a frequency comparable to that of the mechanical resonator and, therefore much lower than the optical frequency. We demonstrate that this hybrid effect is a direct consequence of the virtual photon population in the ground state. Within a classical physics analogy, attaching a weight to a spring only changes its resting position, whereas dynamically modulating the weight makes the system oscillate. In our case, however, the weight is the vacuum itself. We propose and accurately characterize a hybrid superconducting-optomechanical setup based on available state-of-the-art technology, where this effect can be experimentally observed.