Polariton cascade phonon laser

TL;DR

This paper introduces a quantum cascade phonon laser that uses polariton condensates in semiconductor devices to generate high-frequency phonons, enabling new integrated optomechanical applications.

Contribution

It proposes and demonstrates a novel unipolar quantum cascade phonon laser based on polariton condensates in semiconductor microstructures.

Findings

Achieved stimulated phonon emission at 20, 60, and 100 GHz.

Demonstrated efficient phonon generation via polariton down-cascade.

Opened pathways for integrated high-frequency optomechanical devices.

Abstract

Phonon lasers, as their photon counterparts, rely on the physics of stimulated emission. Arguably, because light does not require a material substrate to propagate, while sound does, the impact of the two technologies has however been highly contrasting, with "sasers" (for sound amplification by stimulated emission of radiation) mostly remaining as an academic curiosity. This might be changing due to the possibility to use coherent sound generation for on-chip processing of information at ultra-high frequencies, and in the quantum realm, in integrated photonic and optomechanical devices. Inspired by the concept of unipolar lasers based on the quantum engineering of states in semiconductor heterostructures, we propose and implement a quantum cascade phonon laser (QCPL). A condensate of exciton-photon quasiparticles (polaritons) is optically induced in a microstructured semiconductor device to jump down a ladder of engineered levels. This down-cascade is accompanied by the efficient stimulated emission of phonons of $\sim 20$, $\sim 60$, and $\sim 100$~GHz, which are designed to strongly interact with the polaritons on the same chip. The proposed concept opens the path for the design of integrated high-frequency optomechanical devices, as for example for non-reciprocal photon transport and multi-wavelength Brillouin lasers.