Abstract
Photon thermalisation and condensation in dye-filled microcavities is a growing area of scientific interest, at the intersection of photonics, quantum optics and statistical physics. We give here a short introduction to the topic, together with an explanation of some of our more important recent results. A key result across several projects is that we have a model based on a detailed physical description which has been used to accurately describe experimental observations. We present a new open-source package in Python called PyPBEC which implements this model. The aim is to enable the reader to readily simulate and explore the physics of photon condensates themselves, so this article also includes a working example code which can be downloaded from the GitHub repository.
Highlights
When the coupling between light and matter is coherent, this is known as the strong-coupling regime of cavity quantum electrodynamics (CQED)
There is a simpler, incoherent form of strong coupling between light and matter, which is reached when the absorption of light by the gain medium is at least as fast as loss from the resonator. This is the regime in which photon thermalisation to room temperature and BoseEinstein condensation (BEC) [8] can occur, and this regime is the topic of this work
We review some of our group’s recent experimental and theoretical results, with the perspective that photon condensation is an example of a wider class of dynamical phase transitions, from which one can learn a lot about phase transitions in general
Summary
Steady-state photon populations were categorised as functions of pump and absorption rates relative to cavity loss rate. For the simulation parameters used, the population of a mode was found to jump by at least a factor 100 in a range of about 10% variation in pump rate, which provided a working definition of a phase transition. Our apparatus allows us to measure the populations of individual energy levels, and we use those populations to assign phases to regions of experimental-parameter space (pump laser power and cavity length). The dynamics of phase transitions We turn to dynamical results (away from steady state), after quenches (theory work) and pulses (experiments). We conclude that the BEC phase transition is caused by (deterministic) stimulated scattering/emission but can only occur after (stochastic) spontaneous scattering of photons into the condensing mode. It is important to have an accurate theory of the system based on a fundamentally
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