Observation of non-Hermitian degeneracies in a chaotic exciton-polariton billiard
Observation of non-Hermitian degeneracies in a chaotic exciton-polariton billiard
复制标题
DOI：
10.1038/nature15522
复制
发表时间：
2015-10-22
期刊：
影响因子：
64.8
通讯作者：
Ostrovskaya, E. A.
中科院分区：
文献类型：
--
作者：
Gao, T.;Estrecho, E.;Ostrovskaya, E. A.
激子-极化激元是半导体微腔中光子和激子（电子-空穴对）强烈相互作用形成的混合轻物质准粒子（1-3）。它们已经成为下一代光电应用以及量子多体物理基础研究的强大固态平台。重要的是，激子-极化激元是一个非常开放的（即，非厄米（4，5））量子系统，它需要不断泵浦能量并不断衰变，释放相干辐射（6）。因此，激子-极化激元总是存在于一个平衡的潜在景观的增益和损失。然而，这种势的固有非厄米性质迄今为止在激子-极化激元物理学中很大程度上被忽略了。在这里，我们证明了非厄米性极大地改变了激子-极化激元系统中的模式结构和光谱简并性，因此，将影响它们的量子输运，局域化和动力学性质（7-9）。利用空间结构光泵（10-12），我们产生了一个混沌激子-极化子台球-一个由弯曲势垒包围的二维区域。这个台球的本征模表现出多个非厄米谱简并，称为例外点（13，14）。这些点可以引起显著的波动现象，例如单向传输（15）、异常激光/吸收（16，17）和手征模式（18）。通过改变台球的参数，我们观察到能级的交叉和反交叉，并揭示了非厄米系统独有的非平凡拓扑模态结构（9，13 -22）。我们还观察到模式切换和拓扑Berry相位的参数环包围例外点（23，24）。我们的发现为激子-极化激元的非厄米量子动力学研究铺平了道路，这可能会揭示基于极化激元的器件的新工作原理。
Exciton-polaritons are hybrid light-matter quasiparticles formed by strongly interacting photons and excitons (electron-hole pairs) in semiconductor microcavities(1-3). 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-Hermitian(4,5)) quantum system, which requires constant pumping of energy and continuously decays, releasing coherent radiation(6). 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 properties(7-9). Using a spatially structured optical pump(10-12), 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 points(13,14). Such points can cause remarkable wave phenomena, such as unidirectional transport(15), anomalous lasing/absorption(16,17) and chiral modes(18). 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 systems(9,13-22). We also observe mode switching and a topological Berry phase for a parameter loop encircling the exceptional point(23,24). 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.