Quantum theory of intersubband polarons

TL;DR

This paper develops a microscopic quantum theory of intersubband polarons, revealing extremely strong coupling between intersubband transitions and optical phonons, with potential applications in optoelectronics and quantum physics.

Contribution

It introduces a second quantized model incorporating both Fröhlich and Coulomb interactions, highlighting the possibility of ultrastrong coupling regimes in intersubband polarons.

Findings

Coupling is strong enough to resolve spectral splitting.

Coupling can reach the ultrastrong regime, comparable to excitation frequencies.

Potential applications in optoelectronics and quantum vacuum physics.

Abstract

We present a microscopic quantum theory of intersubband polarons, quasiparticles originated from the coupling between intersubband transitions and longitudinal optical phonons. To this aim we develop a second quantized theory taking into account both the Fr\"ohlich interaction between phonons and intersubband transitions and the Coulomb interaction between the intersubband transitions themselves. Our results show that the coupling between the phonons and the intersubband transitions is extremely intense, thanks both to the collective nature of the intersubband excitations and to the natural tight confinement of optical phonons. Not only the coupling is strong enough to spectroscopically resolve the resonant splitting between the modes (strong coupling regime), but it can become comparable to the bare frequency of the excitations (ultrastrong coupling regime). We thus predict the possibility to exploit intersubband polarons both for applied optoelectronic research, where a precise control of the phonon resonances is needed, and also to observe fundamental quantum vacuum physics, typical of the ultrastrong coupling regime.