# Phonon induced optical gain in a current carrying two-level quantum dot

## TL;DR

This paper investigates how a current-carrying two-level quantum dot coupled to a phonon bath can exhibit optical gain and lasing due to population inversion, with the phenomenon depending on bias voltage and system parameters.

## Contribution

It demonstrates phonon-induced optical gain and lasing in a quantum dot system, analyzing the conditions for different absorption regimes and population inversion effects.

## Key findings

- Lasing occurs at high bias voltages due to population inversion.
- The lasing frequency depends on level spacing and phonon frequency.
- The electron-phonon coupling strength does not affect the lasing frequency.

## Abstract

In this work we consider a current carrying two level quantum dot(QD) that is coupled to a single mode phonon bath. Using self-consistent Hartree-Fock approximation, we obtain the I-V curve of QD. By considering the linear response of our system to an incoming classical light, we see that depending on the parametric regime, the system could have weak or strong light absorption or may even show lasing. This lasing occurs at high enough bias voltages and is explained by a population inversion considering side bands, while the total electron population in the higher level is less than the lower one. The frequency at which we have the most significant lasing depends on the level spacing and phonon frequency and not on the electron-phonon coupling strength.