# Third sound detectors in accelerated motion

## TL;DR

This paper proposes an experiment using a laser beam in circular motion to detect the Unruh effect via third sound waves in superfluid helium-4, accounting for realistic initial temperatures and demonstrating feasible observation of acceleration-dependent signals.

## Contribution

It introduces a novel experimental setup to observe the Unruh effect with superfluid helium-4, including a theoretical framework for non-zero initial temperatures.

## Key findings

- Acceleration-dependent signal persists regardless of initial temperature
- Signal-to-noise ratio indicates experimental feasibility
- The proposed method can detect observer-dependent particle responses

## Abstract

An accelerated observer moving through empty space sees particles appearing and disappearing, while an observer with a constant velocity does not register any particles. This phenomenon, generally known as the Unruh effect, relies on an initial vacuum state, thereby unifying the experience of all inertial observers. We propose an experiment to probe this observer-dependent detector response, using a laser beam in circular motion as a local detector of superfluid helium-4 surface modes or third sound waves. To assess experimental feasibility, we develop a theoretical framework to include a non-zero temperature initial state. We find that an acceleration-dependent signal persists, independent of the initial temperature. By introducing a signal-to-noise measure we show that observing this signal is within experimental reach.