Breakthrough in Mid-Infrared Single-Photon Generation Opens New Frontiers for Quantum Technologies

Researchers at the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at CFEL in collaboration with DTU Electro, the University of Sheffield and the University of Copenhagen, have proposed a novel method for efficiently generating single photons in the mid-infrared (MIR) range. This theoretical breakthrough, published in Science Advances, has the potential to revolutionize quantum technologies by enabling new applications in molecular sensing, precision metrology, and quantum communication.

A schematic of the MIR-photon generation protocol. (Left) Schematic of a quantum emitter (QE) with energy ℏω0 coupled to an optical cavity with energy ℏωc and light-matter coupling strength ℏgVis, interacting with a polar phonon mode of energy ℏΩν . The phonon mode is then coupled to a plasmonic or dielectric antenna tuned to its resonance, with coupling strength ℏgIR. The middle and right panels show the two-step photon generation protocol: (i) an initially excited quantum emitter emits a photon in the visible via the first phonon sideband, which is Purcell enhanced through the cavity interaction. The emitted photon is used to herald the generation of a single phonon. (ii) The phonon then radiates as a single MIR photon through the interaction with the MIR antenna structure.

Single photons are essential for quantum metrology and precision spectroscopy, where they significantly enhance measurement accuracy. While most existing single-photon sources (SPEs) operate in the visible and near-infrared ranges, their efficiency declines significantly in the MIR and terahertz domains. Advancing MIR single-photon sources could enable groundbreaking applications, such as non-invasive biological imaging, pollutant detection in biological fluids, and in-depth studies of molecular vibrations.

In the study, researchers developed a technique that leverages the coupling between visible-frequency single-photon sources and phonons—vibrational modes of a material’s crystal lattice—to generate single MIR photons. According to Nicolas Stenger, Associate Professor at DTU Electro, “the process enhances specific optical transitions, first preparing a phonon mode in a quantum state before converting it into a single MIR photon via a specially designed antenna. This method not only enables on-demand single-photon generation but is also adaptable to a wide range of quantum emitters, including two-dimensional materials, nanocrystals, and molecular systems.”

“By unlocking single-photon generation in the MIR regime, we are opening the door to more precise molecular studies and potential breakthroughs in fields such as drug development and materials science,” explains Mark Kamper Svendsen, junior professor at the University of Copenhagen and a former researcher at MPSD, and first author of this work with Jake Iles-Smith from the University of Sheffield.

“This work marks a major step forward in harnessing quantum light for practical applications and sets the stage for experimental validation and future technological advancements,” says Angel Rubio, Director of the Theory Department at the MPSD. The results pave the way for further exploration of cavity-engineered solid-state materials and the expansion of quantum electrodynamics (QED) in material science.

Text based on DTU’s press release about this work.