Terahertz Quantum Cascade Lasers as Enabling Quantum Technology

Quantum cascade lasers (QCLs) represent the most fascinating achievement of quantum engineering, showing how artificial materials can be generated through quantum design, with tailor-made properties. Their inherent quantum nature deeply affects their core physical parameters. QCLs indeed display intrinsic linewidths approaching the quantum limit, and show spontaneous phase-locking of their emitted modes via intracavity four-wave-mixing, meaning that they can naturally operate as miniaturized metrological frequency rulers, also in frontier frequency domains, as the far-infrared, yet unexplored in quantum science. Here, the authors discuss the fundamental quantum properties of QCLs operating at terahertz frequencies and their key technological performances, highlighting future perspectives of this frontier research field in disruptive areas of quantum technologies such as quantum sensing, quantum metrology, quantum imaging, and photonic-based quantum computation.