External seminar archive:

Bose-Einstein condensation of just a few photons

23 May 2019
Dr Benjamin Walker, Imperial College London

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).