Quantum measurements using single-photon detectors are opening interesting new perspectives in diverse fields such as remote sensing, quantum cryptography and quantum computing. A particularly demanding class of applications relies on the simultaneous detection of correlated single photons. In the visible and near infrared wavelength ranges suitable single-photon detectors do exist. However, low detector quantum efficiency or excessive noise has hampered their mid-infrared (MIR) counterpart. Fast and highly efficient single-photon detectors are thus highly sought after for MIR applications. Here we pave the way to quantum measurements in the MIR by the demonstration of a room temperature coincidence measurement with non-degenerate twin photons at about 3.1 μm. The experiment is based on the spectral translation of MIR radiation into the visible region, by means of efficient up-converter modules. The up-converted pairs are then detected with low-noise silicon avalanche photodiodes without the need for cryogenic cooling.

Mid-infrared integrated quantum photonics is a promising platform for applications in sensing and metrology. However, there are only a few examples of on-chip single-photon sources at these wavelengths. These have limited performances with respect to their C-band counterparts. In this work, we demonstrate a new approach to generate heralded single photons in the mid-infrared on a silicon chip. By using a standard C-band pump, the inter-modal spontaneous four-wave mixing enables the generation of the herald idler at 1259.7 nm and the heralded signal at 2015 nm. The idler photon is easily detected with a common infrared single-photon detector while the signal photon is upconverted to visible before its detection. In this way, we are able to operate a mid-infrared source without the need for mid-infrared detectors and laser sources. By measuring a heralded g (2) of 0.23 ± 0.08, we demonstrate the single-photon behavior of the source as well as the feasibility of multi-photon coincidence measurements beyond 2 μm with our setup. The source exhibits a high-intrinsic heralding efficiency of (59 ± 5)%, a maximum coincidence to accidental ratio of 40.4 ± 0.9, and a generation probability of (0.70 ± 0.10) W −2 .

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Piccione, S.; Mancinelli, M.; Trenti, A.; Fontana, G.; Dam, J.; Tidemand-Lichtenberg, Peter; Pedersen, C.; Pavesi, L. ABSTRACTIn the last years, the Mid Infrared (MIR) spectral region has attracted the attention of many areas of science and technology, opening the way to important applications, such as molecular imaging, remote sensing, freespace communication and environmental monitoring. However, the development of new sources of light, such as quantum cascade laser, was not followed by an adequate improvement in the MIR detection system, able to exceed the current challenges. Here we demonstrate the single-photon counting capability of a new detection system, based on efficient up-converter modules, by proving the correlated nature of twin photons pairs at about 3.1μm, opening the way to the extension of quantum optics experiments in the MIR.

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