Bose-Einstein condensation of photons in a vertical-cavity surface-emitting laser

TL;DR

This paper demonstrates Bose-Einstein condensation of photons in a vertical-cavity surface-emitting laser, revealing equilibrium-like behavior and potential for superfluid photon physics and high-power single-mode emission.

Contribution

It provides the first observation of photon Bose-Einstein condensation in a broad-area VCSEL with positive detuning, linking laser physics with quantum statistical phenomena.

Findings

Bose-Einstein condensate observed in the fundamental mode at critical phase-space density

Experimental results follow the equation of state for a 2D boson gas in thermal equilibrium

Spectral temperatures are lower than device temperatures, indicating driven-dissipative effects

Abstract

Many bosons can occupy a single quantum state without a limit. This state is described by quantum-mechanical Bose-Einstein statistics, which allows the formation of a Bose-Einstein condensate at low temperatures and high particle densities. Photons, historically the first considered bosonic gas, were late to show this phenomenon, which was observed in rhodamine-filled microlaser cavities and doped fiber cavities. These more recent findings have raised the natural question as to whether condensation is common in laser systems, with potential technological applications. Here, we show the Bose-Einstein condensation of photons in a broad-area vertical-cavity surface-emitting laser with positive cavity mode-gain peak energy detuning. We observed a Bose-Einstein condensate in the fundamental transversal optical mode at the critical phase-space density. The experimental results follow the equation of state for a two-dimensional gas of bosons in thermal equilibrium, although the extracted spectral temperatures were lower than those of the device. This is interpreted as originating from the driven-dissipative nature of the device and the stimulated cooling effect. In contrast, non-equilibrium lasing action is observed in the higher-order modes in a negatively detuned device. Our work opens the way for the potential exploration of superfluid physics of interacting photons mediated by semiconductor optical non-linearities. It also shows great promise for enabling single-mode high-power emission from a large aperture device.