Atto-Watt Photo-Detection at Mid-Infrared Wavelengths by a Room-Temperature Balanced Heterodyne Set-Up

Year: 2025

Authors: Mancini L., Ulpiani P., Vecchi C., Daga L., Proietti M., Liorni C., Dispenza M., Cappelli F., De Natale P., Borri S., Palaferri D.

Autors Affiliation: GEM Elettron SRL, Photon Res & Appl Nav Sci Lab, Via Amerigo Vespucci 9, I-63074 San Benedetto Tronto, Italy; Leonardo Innovat Labs, Via Tiburtina Km 12400, I-00131 Rome, Italy; CNR, Ist Nazl Ott, Largo E Fermi 6, I-50125 Florence, Italy.

Abstract: Balanced heterodyne detection (BHD) is a key technology at visible and near-infrared wavelengths for quantum communication and quantum sensing applications based on coherent read-out schemes. Extending BHD at mid-infrared wavelengths (4-11 mu m), given the reduced scattering and favourable transparent atmospheric windows, could enable robust earth-satellite links and few-photon imaging in high-noise environments. Currently, quantum applications at these wavelengths are hindered by the lack of high-sensitivity, room-temperature photoreceivers; moreover, mid-infrared single-photon-detectors reported to date (superconductors, single-electron-transistors, or avalanche-photodiodes) require cryogenic operation, limiting practicality. Here, a room-temperature BHD system operating at 4.6 mu m-wavelength with atto-watt sensitivity level, corresponding to a few tens of photons per second, is demonstrated. This result is obtained by selecting commercially available photodetectors with the highest detectivity and exploiting two heterodyne setups -one involving a single quantum-cascade-laser (QCL) and an acousto-optic-modulator (AOM), and the other one including two QCLs with mutual coherence ensured by a phase-locked-loop. Combining a sufficiently high local oscillator (LO) power and the high phase-coherence between signal and LO is crucial to push the system noise-equivalent-power (NEP) to values approaching the shot-noise-limit, as confirmed by few-photons interferometry measurements. This work not only validates viable methods to detect ultra-low-intensity signals, but is also potentially scalable to the entire wavelength range already accessible by state-of-the-art mid-infrared technology.

Journal/Review: LASER & PHOTONICS REVIEWS

More Information: This project has received funding from the European Defence Fund (EDF) under Grant No. 101103417 EDF-2021-DIS-RDIS-ADEQUADE. D.P., L.M., C.V., and L.D. acknowledge funding from the European Union’s Horizon Europe research and innovation program under the project INPHOMIR (Grant No. 101135749 HORIZON-CL4-2023-DIGITAL-EMERGING-01). F.C., P.D.N., and S.B. acknowledge funding from the European Union’s NextGenerationEU Programme with the I-PHOQS Infrastructure (IR0000016, ID D2B8D520) Integrated infrastructure initiative in Photonic and Quantum Sciences. Funded by the European Union. Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission, or the European Health and Digital Executive Agency (HADEA). Neither the European Union nor the granting author ity can be held responsible for them. L.M. and P.U. contributed equally to this work. S.B. and D.P. equally supervised this work.
KeyWords: balanced heterodyne detection; mid-infrared; quantum cascade laser
DOI: 10.1002/lpor.202501339