Bose–Einstein condensation of photons in an optical microcavity

By J. Klaers, J. Schmitt, F. Vewinger, M. Weitz. Nature, 2010

692 citations recorded by the source corpus.

Bose–Einstein condensation (BEC)—the macroscopic ground-state accumulation of particles with integer spin (bosons) at low temperature and high density—has been observed in several physical systems, including cold atomic gases and solid-state quasiparticles. However, the most omnipresent Bose gas, blackbody radiation (radiation in thermal equilibrium with the cavity walls) does not show this phase transition. In such systems photons have a vanishing chemical potential, meaning that their number is not conserved when the temperature of the photon gas is varied; at low temperatures, photons disappear in the cavity walls instead of occupying the cavity ground state. Theoretical works have considered thermalization processes that conserve photon number (a prerequisite for BEC), involving Compton scattering with a gas of thermal electrons or photon–photon scattering in a nonlinear resonator configuration. Number-conserving thermalization was experimentally observed for a two-dimensional photon gas in a dye-filled optical microcavity, which acts as a ‘white-wall’ box. Here we report the observation of a Bose–Einstein condensate of photons in this system. The cavity mirrors provide both a confining potential and a non-vanishing effective photon mass, making the system formally equivalent to a two-dimensional gas of trapped, massive bosons. The photons thermalize to the temperature of the dye solution (room temperature) by multiple scattering with the dye molecules. Upon increasing the photon density, we observe the following BEC signatures: the photon energies have a Bose–Einstein distribution with a massively populated ground-state mode on top of a broad thermal wing; the phase transition occurs at the expected photon density and exhibits the predicted dependence on cavity geometry; and the ground-state mode emerges even for a spatially displaced pump spot. The prospects of the observed effects include studies of extremely weakly interacting low-dimensional Bose gases and new coherent ultraviolet sources.

Subfields: Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/d917aaa6a81fb5615aaa52e56c75517af4b29397

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Citations in the corpus

Artificial gauge fields in materials and engineered systems (2017, positive): “The realization of the Bose–Einstein condensation of photons in such physical systems [97] brings novel perspectives in quantum simulation with optical photons.”
Optical wave turbulence: Towards a unified nonequilibrium thermodynamic formulation of statistical nonlinear optics (2014, background): “In the experiments [405,77] the authors achieve a number conserving thermalization process by considering a dye-filled optical micro-resonator, which plays the role of a ‘white-wall box’ for the two dimensional photon gas.”
Keldysh field theory for driven open quantum systems (2015, background): “Similar physics can also arise in a variety of other systems, including condensates of photons [151], magnons [152], and potentially excitons [153].”
Breakdown of Photon Blockade: A Dissipative Quantum Phase Transition in Zero Dimensions (2013, background): “Notable experiments are the realization of the Dicke quantum phase transition [43–45] through photon scattering from a superfluid gas in an optical cavity [46] and the observation of Bose-Einstein condensation of photons in an optical microcavity [47].”
Recent advances in solid-state organic lasers (2011, background): “Let’s notice that in optical microcavities, another exotic regime has been experimentally demonstrated for the first time in 2010 using dye molecules, namely a Bose-Einstein Condensate (BEC) of photons [184].”
Topological photonics (2018, background): “Except for very specific cases (Rasmussen et al., 2000; Silberberg et al., 2009; Klaers et al., 2010; Hafezi, Adhikari, and Taylor, 2015; Lebreuilly et al., 2017), the resulting state of the light field is thus quite distinct from a thermal equilibrium state.”
Supercurrent in a room-temperature Bose–Einstein magnon condensate (2015, background): “interacting quasiparticles such as photons [16], plasmonexciton polaritons [17] or magnons [18, 19].”