Quantum-Level Crosstalk Characterization of a 16x16 MEMS Optical Switch for Dynamic Quantum Communications

As quantum networks expand, there is a growing need to integrate commercial, off-the-shelf photonic components—such as MEMS optical switches—to manage complex, multi-user network topologies. This study investigates whether the crosstalk (photon leakage) inherent in a commercial 16x16 MEMS optical switch is low enough to allow for the coexistence of quantum channels without compromising the security or performance of Quantum Key Distribution (QKD) protocols.

The authors performed an all-to-all characterization of a 16x16 MEMS optical switch using superconducting nanowire single-photon detectors (SNSPDs). By systematically routing a classical laser signal through every possible input-output port combination, they measured the resulting photon leakage. They then correlated this empirical data with a theoretical model of the decoy-state BB84 QKD protocol to determine how much crosstalk-induced noise would be required to cause specific levels of Secret Key Rate (SKR) degradation under varying channel loss conditions.

The experimental results reveal that crosstalk in the MEMS switch is highly non-uniform, with specific port combinations exhibiting significantly higher leakage than others. While some configurations showed leakage as high as 2 million counts per second, the majority of port combinations maintained noise levels low enough to support QKD operations even with up to 20 dB of channel attenuation. The study concludes that while careful port management is necessary to avoid high-noise configurations, commercial MEMS switches are a viable, cost-effective solution for dynamic quantum network architectures.

This research provides a practical roadmap for scaling quantum networks. By validating that standard, commercially available optical switches can be used in quantum environments, the authors demonstrate a path toward reducing the cost and complexity of quantum infrastructure, potentially eliminating the need for specialized, custom-built quantum optical components.