The Phononic Casimir Effect: An Analog Model

TL;DR

This paper explores the quantum fluctuations of sound waves in fluids as an analog for quantum field effects, highlighting potential observable phenomena related to boundaries and squeezed states.

Contribution

It introduces the quantization of sound in fluids as an analog model for quantum field boundary effects, including density fluctuations and their impact on light scattering.

Findings

Density fluctuations are small but potentially observable at room temperature.

Boundaries reduce mean squared density fluctuations and light scattering cross section.

Squeezed phonon states modify the quantum fluctuations in the fluid.

Abstract

We discuss the quantization of sound waves in a fluid with a linear dispersion relation and calculate the quantum density fluctuations of the fluid in several cases. These include a fluid in its ground state. In this case, we discuss the scattering cross section of light by the density fluctuations, and find that in many situations it is small compared to the thermal fluctuations, but not negligibly small and might be observable at room temperature. We also consider a fluid in a squeezed state of phonons and fluids containing boundaries. We suggest that the latter may be a useful analog model for better understanding boundary effects in quantum field theory. In all cases involving boundaries which we consider, the mean squared density fluctuations are reduced by the presence of the boundary. This implies a reduction in the light scattering cross section, which is potentially an observable effect.