Observation of non-Hermitian degeneracies in a chaotic exciton-polariton billiard
Oct 12, 2015Citations per year
Abstract: (Springer)
In non-Hermitian systems, spectral degeneracies can arise that can cause unusual, counter-intuitive effects; here exciton-polaritons—hybrid light–matter particles—within a semiconductor microcavity are found to display non-trivial topological modal structure exclusive to such systems. In non-Hermitian systems, which are open and subject to gain and loss, exceptional points can arise, spectral degeneracies that can cause unusual, counter-intuitive effects. Recent efforts to observe non-Hermitian physics have concentrated on various optical systems, but not yet on exciton-polaritons. These are hybrid light–matter particles, formed by strongly interacting photons and excitons (electron–hole pairs) in semiconductor microcavities. Such systems require constant pumping of energy and continuously decays releasing coherent radiation, so are a profoundly open quantum system. In a striking experiment involving a chaotic exciton-polariton billiard —a two-dimensional area enclosed by a curved potential barrier — these authors demonstrate this non-Hermitian nature for the first time. The experiment reveals the non-trivial topological modal structure exclusive to non-Hermitian systems. These findings open the way for novel types of operating principles for polariton-based optoelectronic devices. Exciton-polaritons are hybrid light–matter quasiparticles formed by strongly interacting photons and excitons (electron–hole pairs) in semiconductor microcavities1,2,3. They have emerged as a robust solid-state platform for next-generation optoelectronic applications as well as for fundamental studies of quantum many-body physics. Importantly, exciton-polaritons are a profoundly open (that is, non-Hermitian4,5) quantum system, which requires constant pumping of energy and continuously decays, releasing coherent radiation6. Thus, the exciton-polaritons always exist in a balanced potential landscape of gain and loss. However, the inherent non-Hermitian nature of this potential has so far been largely ignored in exciton-polariton physics. Here we demonstrate that non-Hermiticity dramatically modifies the structure of modes and spectral degeneracies in exciton-polariton systems, and, therefore, will affect their quantum transport, localization and dynamical properties7,8,9. Using a spatially structured optical pump10,11,12, we create a chaotic exciton-polariton billiard—a two-dimensional area enclosed by a curved potential barrier. Eigenmodes of this billiard exhibit multiple non-Hermitian spectral degeneracies, known as exceptional points13,14. Such points can cause remarkable wave phenomena, such as unidirectional transport15, anomalous lasing/absorption16,17 and chiral modes18. By varying parameters of the billiard, we observe crossing and anti-crossing of energy levels and reveal the non-trivial topological modal structure exclusive to non-Hermitian systems9,13,14,15,16,17,18,19,20,21,22. We also observe mode switching and a topological Berry phase for a parameter loop encircling the exceptional point23,24. Our findings pave the way to studies of non-Hermitian quantum dynamics of exciton-polaritons, which may uncover novel operating principles for polariton-based devices.- Bose–Einstein condensates
- Matter waves and particle beams
- Polaritons
- Quantum fluids and solids
References(41)
Figures(0)