Non-Hermitian Phase Transition from a Polariton Bose-Einstein Condensate to a Photon Laser

Ryo Hanai, Alexander Edelman, Yoji Ohashi, Peter B. Littlewood

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)


We propose a novel mechanism for a nonequilibrium phase transition in a U(1)-broken phase of an electron-hole-photon system, from a Bose-Einstein condensate of polaritons to a photon laser, induced by the non-Hermitian nature of the condensate. We show that a (uniform) steady state of the condensate can always be classified into two types, namely, arising either from lower or upper-branch polaritons. We prove (for a general model) and demonstrate (for a particular model of polaritons) that an exceptional point where the two types coalesce marks the end point of a first-order-like phase boundary between the two types, similar to a critical point in a liquid-gas phase transition. Since the phase transition found in this paper is not in general triggered by population inversion, our result implies that the second threshold observed in experiments is not necessarily a strong-to-weak-coupling transition, contrary to the widely believed understanding. Although our calculation mainly aims to clarify polariton physics, our discussion is applicable to general driven-dissipative condensates composed of two complex fields.

Original languageEnglish
Article number185301
JournalPhysical review letters
Issue number18
Publication statusPublished - 2019 May 8

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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