Intensity correlations in quantum cascade laser harmonic frequency combs

TL;DR

This paper investigates intensity correlations in quantum cascade laser harmonic frequency combs, revealing potential for quantum light sources and discussing technological limits and future detection methodologies.

Contribution

It demonstrates the presence of intensity correlations in QCL harmonic combs driven by Four-Wave Mixing, advancing understanding of their quantum properties.

Findings

Intensity correlations observed between twin modes.

Discussion of limits of current technology.

Potential pathways for detecting non-classical phenomena.

Abstract

A novel study on harmonic frequency combs emitted by Quantum Cascade Lasers (QCLs) is here presented, demonstrating the presence of intensity correlations between twin modes characterising the emission spectra. These originate from a Four-Wave Mixing (FWM) process driven by the active medium's third-order non-linearity. The study of such correlations is essential for the engineering of a new generation of semiconductor devices with the potential of becoming integrated emitters of light with quantum properties, such as squeezing and entanglement. Starting from experimental results, the limits of state-of-the-art technology are discussed as well as the possible methodologies that could lead to the detection of non-classical phenomena, or alternatively improve the design of QCLs, in the compelling perspective of generating quantum correlations in mid-infrared light.