Observation of the formation of long-range order during superradiant emission in a high-density e-h system

TL;DR

This paper reports the experimental observation of long-range temporal and spatial coherence in a high-density electron-hole system in GaAs during femtosecond superradiant emission at room temperature, indicating the formation of a macroscopically ordered quantum state.

Contribution

It provides the first experimental evidence of long-range order formation during superradiant emission in a high-density e-h system at room temperature.

Findings

Observation of long-range temporal coherence.

Detection of spatial phase coherence.

Evidence of macroscopically ordered quantum state.

Abstract

The transition of atomic, electronic, or e-h systems to quantum phases is an extraordinary process when both microscopic and macroscopic properties of the system undergo fundamental changes. Bose-Einstein condensation, has been observed in a number of physical systems, including super-cold atomic gases and solid- state quasiparticles. The most typical example of equilibrium condensation is the superconducting state of Cooper pairs in metals. However, in many cases the lifetime of particles or quasiparticles under study is finite, ranging from picoseconds to milliseconds. And even in this case condensation is possible. It is generally understood at present that coherence and off-diagonal long-range order in the density matrix are the most important characteristic features of condensed quantum states. Phase coherence established over microscopic distances is an intrinsic property of all Bose condensates. Experiments featuring interference between either two condensates or two separate parts of the same condensate are often considered as more convincing than observation of the macroscopic occupation of the ground state. The formation of long-range order and spatial phase coherence can be measured by studying interference patterns using either a Michelson interferometer or Young double slit arrangement. Here we present experimental results of observation of long-range temporal and spatial coherence of a macroscopically ordered state of a high-density e-h system in GaAs during the generation of femtosecond superradiant emission at room temperature