arXiv:1510.05562 · New Journal of Physics

Spatiotemporal coherence of non-equilibrium multimode photon condensates

Jakov Marelic, Lydia Neary‐Zajiczek, Henry J Hesten, Kon H Leung, Edward Y X Ong, Florian Mintert, Robert A. Nyman

Published Oct 12, 2016• 46 citations

Abstract

We report on the observation of quantum coherence of Bose–Einstein condensed photons in an optically pumped, dye-filled microcavity. We find that coherence is long-range in space and time above condensation threshold, but short-range below threshold, compatible with thermal-equilibrium theory. Far above threshold, the condensate is no longer at thermal equilibrium and is fragmented over non-degenerate, spatially overlapping modes. A microscopic theory including cavity loss, molecular structure and relaxation shows that this multimode condensation is similar to multimode lasing induced by imperfect gain clamping.

DOI: 10.1088/1367-2630/18/10/103012

Related papers

Spatiotemporal coherence of non-equilibrium photon condensates

Jakov Marelic, Lydia Neary‐Zajiczek, Robert A. Nyman

Spontaneously formed coherence is the hallmark of condensation of identical bosons. Here we study the coherence of condensates of photons in a dye-filled microcavity, which is a two-dimensional, dissipative system. Our interferometer permits us to measure coherence as a function of both space and time, above and below condensation threshold pump power. We find that coherence is long range in both time and space above threshold, but short-range below threshold, consistent with thermal equilibrium at room temperature. Far above threshold, the condensate is no longer at equilibrium and is fragmented over non-degenerate, spatially-overlapping modes.

Oct 19, 20150 citations

Nonequilibrium Model of Photon Condensation

Peter Kirton, Jonathan Keeling

We develop a nonequilibrium model of condensation and lasing of photons in a dye filled microcavity. We examine in detail the nature of the thermalization process induced by absorption and emission of photons by the dye molecules, and investigate when the photons are able to reach a thermal equilibrium Bose-Einstein distribution. At low temperatures, or large cavity losses, the absorption and emission rates are too small to allow the photons to reach thermal equilibrium and the behavior becomes more like that of a conventional laser.

arXiv:1303.3459Physical Review LettersSep 4, 2013162 citations

Bose-Einstein condensation of photons

Jakov Marelic

A Bose-Einstein condensate can be made of photons. The photons are held at thermodynamic equilibrium in a dye-filled microcavity and pumped with a laser. Thermalisation can be demonstrated and above the threshold a Bose-Einstein condensate will form. A Mach-Zehnder interferometer is built and used to measure the spatial and temporal first-order coherence under various conditions. We build a momentum-resolved spectrometer and use it to obtain views into the phase-space distribution of the photon condensate. We put an upper bound on the value of the interaction strength parameter and find that the microcavity system is ergodic even when not at thermal equilibrium. We build a setup to stabilise the pump laser power with the aim to observe the λ-point of the condensate.

Oct 1, 20170 citations

Photon Bose-Einstein Condensation in a Dye-Filled Microcavity

Karindra Perrier

Bose-Einstein condensation (BEC) is the transition to a macroscopic occupation of the ground state of a system of bosonic particles. In 1995 the first experimental realization of BEC was achieved by condensing a dilute atomic gas [1,2]. It was long thought only massive particles could undergo BEC. However, in 2010 it was shown that photon BEC was achieved in an optical dye-filled microcavity [3]. In 2015, we became the second group to successfully repeat these experiments.\n\nBEC is a phase transition and thus it occurs at thermal equilibrium. To achieve a thermal photon gas the cavity is filled with a fluorescent dye solution. The dye molecules thermalize the photons by means of repeated absorption-emission cycles. We optically pump the cavity. With the pump we determine the number of photons absorbed by the dye, consequently defining a nonvanishing chemical potential. This ensures a conserved photon number. The photons are trapped by the harmonic potential induced by the concave cavity mirrors. Due to the cutoff energy determined by the cavity length, the trapped photons have a dispersion similar to that of a massive particle in a quantum harmonic oscillator. The cavity length is tuned such that the free spectral range is larger than the bandwidth of the dye. Therefore, only one longitudinal mode fits inside the cavity, making the photon gas effectively two-dimensional. We end up with a thermalized two-dimensional photon gas that has the eigenenergies of a quantum harmonic oscillator. The Bose-Einstein distribution function predicts a critical photon number. Pumping the thermal photon gas beyond this critical number will lead to photon BEC.\n\nWe measure the spectral- and spatial distributions of our two-dimensional photon gas. In both distributions we observe photon BEC. Results show the characteristics of a phase transition: the appearance of a sharp peak on top of the thermal cloud that coincides with a converging chemical potential to zero. Both the spectral- and spatial distribution are in agreement with the theoretical distribution of photons with an effective mass in a quantum harmonic oscillator. Expansion of the condensate has been measured. This could indicate nonlinear optical effects such as thermal lensing or repulsive photon-photon interactions.

May 31, 20160 citations

Decondensation in Nonequilibrium Photonic Condensates: When Less Is More

Henry J. Hesten, Robert A. Nyman, Florian Mintert

We investigate the steady state of a system of photons in a pumped dye-filled microcavity. By varying pump and thermalization the system can be tuned between Bose-Einstein condensation, multimode condensation, and lasing. We present a rich nonequilibrium phase diagram which exhibits transitions between these phases, including decondensation of individual modes under conditions that would typically favor condensation.

arXiv:1705.02173Physical Review LettersJan 23, 201841 citations

On the theory and simulation of photonic condensates

Henry J. Hesten

Photons in a dye filled microcavity have been proven to form Bose-Einstein condensates both theoretically and experimentally. The system may also be placed in a fundamentally non- equilibrium state where multiple modes are condensed. This thesis theoretically examines some of the deviations from traditional Bose-Einstein condensate models which have been observed and which may be expected in future experiments. Unusual and potentially unseen condensed states are predicted, along with the unexpected non-critical slowing down of system evolution when in these states. A rigorous derivation of a master equation from a microscopic Hamiltonian is given in chapter two. This is used to study the multimode phases of the condensate in chapter three along with transitions between them. The temporal evolution of the condensate in various phases and close to phase boundaries is presented in chapter four. Dramatic improvements in the simulation of photonic condensates are also discussed in chapter four. These improvements also offer a conceptual shift in the theoretical description of photonic condensates which allows new insights to be made. The fifth chapter establishes a foundation of coupled rate equations which may be used to model the higher order coherences of photons and molecules in future work. Finally the transport of photons across non-standard cavities is modelled, providing guidance for future experiments and possible applications of photonic condensates.

Aug 1, 20190 citations