Controlling a superconducting nanowire single-photon detector using tailored bright illumination

TL;DR

This paper demonstrates that superconducting nanowire single-photon detectors can be controlled using bright illumination, revealing potential security vulnerabilities in quantum key distribution systems.

Contribution

It introduces a method to control superconducting nanowire detectors with bright light, similar to avalanche photodiodes, highlighting security risks.

Findings

Bright light can make the nanowire normally conductive temporarily.

Bright illumination extends the detector's deadtime after photon detection.

Hotspot formation during deadtime exhibits nonlinear sensitivity.

Abstract

We experimentally demonstrate that a superconducting nanowire single-photon detector is deterministically controllable by bright illumination. We found that bright light can temporarily make a large fraction of the nanowire length normally-conductive, can extend deadtime after a normal photon detection, and can cause a hotspot formation during the deadtime with a highly nonlinear sensitivity. In result, although based on different physics, the superconducting detector turns out to be controllable by virtually the same techniques as avalanche photodiode detectors. As demonstrated earlier, when such detectors are used in a quantum key distribution system, this allows an eavesdropper to launch a detector control attack to capture the full secret key without being revealed by to many errors in the key.