Exciton-polariton physics connects broader fields of solid state physics and quantum optics. Our research interests include fundamental properties of exciton-polariton quantum gases, phase transitions far from equilibrium, and mean-field phenomena. We collaborate with leading experimental and theoretical groups in the field.
Exciton-polaritons are very interesting quantum quasiparticles that can find potential applications in various fields, such as extremely accurate interferometric measurements, ultra-low power lasers or information processing with very low energy losses.
Exciton-polaritons are formed in semiconductor materials with a specially designed structure, thanks to the strong coupling of photons and excitons, which are material particles composed of electrons and “holes”. Polaritons possess a “Schrödinger cat” structure. The quantum state contains two alternatives: cat alive when the exciton exists, or dead cat when instead of an exciton a photon exists in the system.
In 2006 came the news that condensation of exciton-polaritons was achieved in a specially prepared semiconductor sample. The idea of Bose-Einstein condensation was sparked in the mid-twenties of the last century, when Albert Einstein, inspired by the Indian physicist Satyendra Nath Bose working on the statistical properties of optical radiation, predicted a particular type of phase transition in the system of non-interacting bosons at temperature close to the absolute zero. In 1938, Fritz London linked this phenomenon with the recently discovered superfluidity of helium, thereby pointing to the first practical application of this rather abstract concept. The observation of a Bose-Einstein condensate of rubidium and sodium gases was achieved much later, in 1995, opening a new chapter in the field of atomic and molecular physics and quantum optics. But only when the condensation of exciton-polaritons was achieved, it could be realized at room temperature, bringing it much closer to real-life applications.
Imagine a crowd of people, each person going in its own direction, sometimes bouncing against the others. This can be thought of as a model of a classical as of particles in a typical thermal state. Now consider an army of soldiers marching at the same pace, moving in unison. This will be the picture of the Bose-Einstein condensate, a quantum gas of bosons at low temperature. From time to time, however, one of the soldiers will do something unexpected, which will break the complete coherence of their movement. This is what happens when quantum fluctuations come into play, which are in fact unavoidable in quantum theory once we consider the individual movements of particles.
A link to a video from the University of Sheffield describing the basics of exciton-polariton physics is provided below.