Nonequilibrium thermodynamics of the acoustoelectric quantum vacuum

This paper investigates the thermodynamic properties of the quantum vacuum in acoustoelectric systems. Specifically, it explores how the kinematics of charge carriers—when drifting at a constant velocity through a semiconducting medium—alter the vacuum state perceived by a mechanical resonator coupled to these carriers.

The authors employ an open quantum systems framework to analyze the interaction between a mechanical oscillator and a bath of plasmons (oscillations of free charge). By deriving the Heisenberg-Langevin equations for the oscillator, they capture the backreaction and noise imparted by the moving charge carriers. The study utilizes the fluctuation-dissipation theorem to demonstrate that the nonequilibrium fluctuations of the vacuum, driven by the drift current, manifest as a thermal state.

The study shows that when charge carriers drift at a velocity $v_d$ exceeding the speed of sound, the vacuum fluctuations are Doppler-shifted. This shift allows for the spontaneous emission of phonon-plasmon pairs, which drives the mechanical resonator into an effective thermal state. The effective temperature $T_{AE}$ is defined by the drift velocity and the spatial frequency $q$ of the mechanical mode ($T_{AE} \approx \hbar v_d q / 2k_B$). For realistic parameters, this temperature can reach several Kelvin, making these systems a viable platform for studying nonequilibrium quantum vacuum effects without requiring relativistic conditions.

This research provides a bridge between quantum field theory and solid-state physics. By demonstrating that thermal-like vacuum effects can be generated in accessible acoustoelectric devices, the paper offers a new, low-energy testbed for exploring phenomena typically associated with high-energy physics, such as the Unruh effect. This could lead to new ways to probe nonequilibrium thermodynamics and quantum vacuum fluctuations in a laboratory setting.