High Performance Superconducting Nanowire Single Photon Detectors for QKD Applications

The forthcoming era of quantum computers can be a threat to the conventional cryptography and data security. Quantum Key Distribution (QKD) provides unconditional security under real-life conditions with several protocols over long distances in fibre and free space communication. Superconducting Nanowire Single Photon Detectors (SNSPDs) are becoming a dominant technology for QKD thanks to their unique characteristics, such as a near-unity efficiency in the infrared, low dark counts and picoseconds time resolution. Where the detector is typically a weakness of QKD, these SNSPDs characteristics make exploitation difficult. In this work, we characterized NbN SNSPDs at 2.2 K, using a CW laser source at 1550 nm, varying both bias currents and input photon rates to prove their high efficiency at low dark counts with a high counting rate, consistent with the requirements for QKD over long distances or with a high secure key rate.