Engineered entropic forces allow ultrastrong dynamical backaction

TL;DR

This paper introduces a method to surpass traditional radiation pressure limits using entropic forces from light absorption, enabling ultrastrong dynamical backaction and low-threshold phonon lasing in superfluid helium.

Contribution

It demonstrates that entropic forces can be engineered to exceed radiation pressure, achieving significantly stronger backaction and lower phonon lasing thresholds than previous approaches.

Findings

Entropic forces can be eight orders of magnitude stronger than radiation pressure.

Achieved phonon lasing with a threshold three orders of magnitude lower.

Developed a framework to engineer dynamical backaction from entropic forces.

Abstract

When confined within an optical cavity, light can exert strong radiation pressure forces. Combined with dynamical backaction, this enables important processes such as laser cooling, and applications ranging from precision sensors to quantum memories and interfaces. However, the magnitude of radiation pressure forces is constrained by the energy mismatch between photons and phonons. Here, we overcome this barrier using entropic forces arising from the absorption of light. We show that entropic forces can exceed the radiation pressure force by eight orders of magnitude, and demonstrate this using a superfluid helium third-sound resonator. We develop a framework to engineer the dynamical backaction from entropic forces, applying it to achieve phonon lasing with a threshold three orders of magnitude lower than previous work. Our results present a pathway to exploit entropic forces in quantum devices, and to study nonlinear fluid phenomena such as turbulence and solitons.