Observation of quantum depletion in a non-equilibrium exciton-polariton condensate.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 31969565.
- Also identified by DOI 10.1038/s41467-019-14243-6 and PMC identifier 6976592.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Superfluidity, first discovered in liquid <sup>4</sup>He, is closely related to Bose-Einstein condensation (BEC) phenomenon. However, even at zero temperature, a fraction of the quantum liquid is excited out of the condensate into higher momentum states via interaction-induced fluctuations-the phenomenon of quantum depletion. Quantum depletion of atomic BECs in thermal equilibrium is well understood theoretically but is difficult to measure. This measurement is even more challenging in driven-dissipative exciton-polariton condensates, since their non-equilibrium nature is predicted to suppress quantum depletion. Here, we observe quantum depletion of a high-density exciton-polariton condensate by detecting the spectral branch of elementary excitations populated by this process. Analysis of this excitation branch shows that quantum depletion of exciton-polariton condensates can closely follow or strongly deviate from the equilibrium Bogoliubov theory, depending on the exciton fraction in an exciton polariton. Our results reveal beyond mean-field effects of exciton-polariton interactions and call for a deeper understanding of the relationship between equilibrium and non-equilibrium BECs.