IEEE Transactions on Applied Superconductivity

Spontaneous Parametric Down Conversion Source Multi-Photon Component Reduction via Photon-Number-Resolving Detector

Ciro Bruscino, Matteo Di Giancamillo, Pasquale Ercolano, A. Porzio, Mikkel Ejrnaes, Daniela Salvoni, Martina Peluso, Chengjun Zhang, Hao Li, Paolo Martelli, L. You, Mario Martinelli, L. Parlato, Giovanni Piero Pepe

Published Mar 30, 2026• 0 citations

Publisher

Abstract

Quantum Key Distribution (QKD) is an optical communication technique that allows two authenticated parties to exchange an encryption key using protocols grounded in the laws of quantum mechanics, making the communication intrinsically secure. A fundamental requirement for key exchange through such protocols is the use of high-performance single-photon detectors and infrared single-photon sources with low multi-photon components. In addition to the rapid progress in single-photon sources (SPSs), achieving the ideal scenario where a source emits only single photons at telecom wavelength with high efficiency remains a theoretical concept. Multi-photon components emitted by non-ideal light sources such as lasers or Spontaneous Parametric Down Conversion (SPDC) sources can open the door to successful attacks from non-legitimate parties. In this work, we demonstrate, by using a Photon-Number-Resolving Detector (PNRD), based on parallel superconducting strips, the possibility of obtaining a single-photon source with extremely multi-photon components starting from a non-single-photon light source, namely an SPDC one. To estimate the reduction of the multi-photon component, we analyzed the second-order autocorrelation function, g(2)(0), of the light source using a PNRD modelled as 8 independent pixels in parallel, in a heralding protocol. We managed to obtain a reduction of the g(2)(0) using a CW SPDC with an emission rate of about 10 MHz using several sampling bin-widths, spanning from less than one nanoseconds to hundreds of nanoseconds. These results align with the goals of the Quantum Italy Deployment project, as sources with suppressed multi-photon components could play a key role in improving the performance of QKD systems.

DOI: 10.1109/tasc.2026.3677328

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