Density matrix theory of transport and gain in quantum cascade lasers in a magnetic field

TL;DR

This paper develops a density matrix framework to analyze electron transport and optical gain in quantum cascade lasers under magnetic fields, highlighting differences between non-Markovian and Markovian models.

Contribution

It introduces a comprehensive quantum kinetic model that incorporates electron-phonon interactions and compares non-Markovian, Markovian, and Boltzmann approaches for quantum cascade lasers.

Findings

Non-Markovian calculations show distinct gain spectra with linewidth and polaronic features.

Current densities are similar across different theoretical approaches despite differing interpretations.

The model captures complex electron dynamics influenced by magnetic fields and phonon interactions.

Abstract

A density matrix theory of electron transport and optical gain in quantum cascade lasers in an external magnetic field is formulated. Starting from the general quantum kinetic treatment, we describe the intra- and inter-period electron dynamics at the non-Markovian, Markovian and Boltzmann approximation levels. Interactions of electrons with longitudinal optical phonons and classical light field are included in the present description. The non-Markovian calculation for a prototype structure reveals significantly different gain spectra in terms of linewidth and additional polaronic features in comparison to the Markovian and Boltzmann ones. Despite strongly opposed interpretations of the origin of the transport processes in the non-Markovian or Markovian and the Boltzmann approaches, they yield comparable values of the current densities.