# The temporal coherence of a photon condensate: A quantum trajectory description

## TL;DR

This paper models the temporal coherence of a photon condensate using a quantum trajectory approach, analyzing effects of interactions and dissipation on coherence properties and validating a laser physics-inspired model.

## Contribution

It introduces a quantum-mechanical model for photon condensate dynamics, including effects of Kerr interactions and dissipation, and validates a laser physics-based heuristic in this context.

## Key findings

- Observation of long-$\tau$ antibunching effect.
- Identification of exponential and Gaussian decay regimes of phase correlations.
- The ratio of coherence times inversely relates to number fluctuations.

## Abstract

In order to study the temporal coherence of a single-mode dye-cavity photon condensate, a model is developed for the dynamics which treats the condensate mode on a quantum-mechanical level. The effects of driving-dissipation and Kerr interactions on the number fluctuations are studied analytically and numerically, including the finding of a long-$\tau$ antibunching effect. Depending on the interaction strength, we quantitatively observe an exponential Schawlow-Townes-like decay or Gaussian Henry-like decay of phase correlations. The adequacy of a heuristic phasor model originating from laser physics in describing number and phase dynamics is validated within the experimentally relevant parameter regime. The ratio of the first and second order coherence times is shown to be inversely proportional to the number fluctuations, with a prefactor that varies smoothly throughout the crossover between canonical and grandcanonical statistics.