Quantum vacuum radiation in optical glass

TL;DR

This paper examines whether observed quantum vacuum radiation in optical glass experiments is truly Hawking radiation or a different quantum vacuum effect, emphasizing the importance of physical effects like pulse steepening and cresting.

Contribution

It challenges the interpretation of experimental results as Hawking radiation and highlights the significance of physical effects that could produce similar observations.

Findings

Naive estimates of quantum vacuum radiation are insufficient.

Pulse steepening and cresting significantly influence radiation estimates.

Dynamical Casimir effect warrants further investigation.

Abstract

A recent experimental claim of the detection of analogue Hawking radiation in an optical system [PRL 105 (2010) 203901] has led to some controversy [PRL 107 (2011) 149401, 149402]. While this experiment strongly suggests some form of particle creation from the quantum vacuum (and hence it is per se very interesting), it is also true that it seems difficult to completely explain all features of the observations by adopting the perspective of a Hawking-like mechanism for the radiation. For instance, the observed photons are emitted parallel to the optical horizon, and the relevant optical horizon is itself defined in an unusual manner by combining group and phase velocities. This raises the question: Is this really Hawking radiation, or some other form of quantum vacuum radiation? Naive estimates of the amount of quantum vacuum radiation generated due to the rapidly changing refractive index --- sometimes called the dynamical Casimir effect --- are not encouraging. However we feel that naive estimates could be misleading depending on the quantitative magnitude of two specific physical effects: "pulse steepening" and "pulse cresting". Plausible bounds on the maximum size of these two effects results in estimates much closer to the experimental observations, and we argue that the dynamical Casimir effect is now worth additional investigation.