Researchers Count Photons in Exciton-Polariton Condensate


Researchers from University of Würzburg analyze condensate of quasiparticles contained in the cavity, by counting the photons emitted from a microcavity

An active medium of laser enters a state in which the atoms sync their emission to produce coherent laser light when the power of the light that drives a laser exceeds the lasing threshold. Previous research has counted photons emitted from a laser to study this coherent state. These researches derived a statistical distribution of the probability that 1, 2, or n photons are emitted at a given time. Now, a research led by Martin Klaas at the University of Würzburg, Germany, performed similar photon-counting experiments to study the novel coherent state of matter known as an exciton-polariton condensate.

Exciton polaritons that arise in semiconductor microcavities are hybrid light-matter quasiparticles. The state in semiconductor microcavities is due to the strong coupling between photons and electron-hole pairs called excitons. Researchers have observed that, exciton polaritons when present in sufficient density, can form a Bose-Einstein condensate (BEC). In this state, all of the particles occupy the same quantum state. The researchers hope to use these condensates to create polariton lasers. Moreover, the condensates can be used to study exotic quantum phases. However, researchers have not understood the complete nature of these BECs. It is unclear whether BCEs act more like lasers or more like condensates of atoms.

Therefore, to further understand the nature of BCEs, the researchers characterized the distribution of photons emitted from exciton polaritons in a micrometer-sized semiconductor pillar. The emitted photons were counted with single-photon precision with the help of a highly sensitive superconducting device known as a transition edge sensor. The measured photon distribution revealed that the exciton-polariton BEC is more closely related to a laser as compared to an atomic condensate. The findings were published in the journal of Physical Review Letters on July 25, 2018.


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