Bose-Einstein Condensation of just a few photons

Photons, like all bosons, exhibit Bose-Einstein condensation (BEC) under the right conditions. In this talk, I will give a brief overview of how these right conditions have been achieved using an optical microcavity, leading to Bose-Einstein condensation [1], before reporting on more recent results pushing such condensates down to the low photon number limit [2]. This low number limit for BEC raises questions, which I address, of how one can mark a condensation thresholds outside of the macroscopic limit.

We use focussed ion beam milling to create mirrors of near arbitrary shapes giving us a high degree of control over the dimensionality and potential landscape of our cavities, and hence the optical modes of the cavity.

I describe how our system can be fully characterised by a dynamical model, which in one limit recaptures complete thermal equilibrium behaviour, and in the other limit recaptures laser behaviour [3] as well as many other interesting non-equilibrium phenomena [4]. This plays into questions of how thermal equilibrium breaks down in driven-dissipative systems.

[1] J. Klaers, J. Schmitt, F. Vewinger, and M. Weitz, Nature 468, 545 (2010)

[2] B. T. Walker, L. C. Flatten, H. J. Hesten, F. Mintert, D. Hunger, A. A. P. Trichet, J. M. Smith, and R. A. Nyman, Nature Physics 14, 1173 (2018)

[3] J. Keeling and P. Kirton, Phys. Rev. A 93, 013829

[4] H. J. Hesten, R. A. Nyman, and F. Mintert, Phys. Rev. Lett. 120, 040601 (2018)

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