SCL Online Seminar by Axel Pelster

You are cordially invited to the SCL online seminar of the Center for the Study of Complex Systems, which will be held on Thursday, 23 December 2021 at 14:00 on Zoom. The talk entitled

On the theoretical description of photon Bose-Einstein condensates

will be given by Dr. Axel Pelster (Department of Physics, Technical University of Kaiserslautern, Germany). Abstract of the talk:

Since the advent of experiments with photon Bose-Einstein condensates in dye-filled microcavities in 2010 [1], many investigations have focused upon the emerging effective photon-photon interaction. Despite its smallness, it can be identified to stem from two physically distinct mechanisms [2]. On the one hand, a Kerr nonlinearity of the dye medium yields a photon-photon contact interaction, whose microscopic theoretical description is based on a Lindblad master equation [3]. On the other hand, a heating of the dye medium leads to an additional thermo-optic interaction, which is both delayed and non-local [4]. The latter turns out to represent the leading contribution to the effective interaction for the current 2D experiments.

A new experimental platform, which is currently built up in Kaiserslautern, will be devoted to analyse the dimensional crossover in trapped photon gases from 2D to 1D. As the photon-photon interaction is generically quite weak, they behave nearly as an ideal Bose gas. Moreover, since the current experiments are conducted in a microcavity, the longitudinal motion is frozen out and the photon gas represents effectively a two-dimensional trapped gas of massive bosons, where the anisotropy of the confinement allows for a dimensional crossover. A detailed investigation for such a system allows to determine its effective dimensionality from thermodynamic quantities [5].

Furthermore, we investigate how the effective photon-photon interaction changes when the system dimension is reduced from 2D to 1D [6]. To this end, we consider an anisotropic harmonic trapping potential and determine via a variational approach how the properties of the photon Bose-Einstein condensate in general, and both aforementioned interaction mechanisms in particular, change with increasing anisotropy. We find that the thermo-optic interaction strength increases at first linearly with the trap aspect ratio and later on saturates at a certain value of the trap aspect ratio. Furthermore, in the strong 1D limit the roles of both interactions get reversed as the thermo-optic interaction remains saturated and the contact Kerr interaction becomes the leading interaction mechanism. Finally, we discuss how the predicted effects can potentially be measured experimentally.

[1] J. Klaers, J. Schmitt, F. Vewinger, and M. Weitz, Nature 468, 545 (2010).
[2] J. Klaers, J. Schmitt, T. Damm, F. Vewinger, and M. Weitz, Appl. Phys. B 105, 17 (2011).
[3] M. Radonjic, W. Kopylov, A. Balaz, and A. Pelster, New J. Phys. 20, 055014 (2018).
[4] E. Stein, F. Vewinger, and A. Pelster, New J. Phys. 21, 103044 (2019).
[5] E. Stein and A. Pelster, arXiv:2011.06339 (2020).
[6] E. Stein and A. Pelster, arXiv:2109.11211 (2021).

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