Photon detectors based on type-2 superconductors have found widespread applications from on-chip quantum computing to quantum remote sensing. Here, we develop the theory for a new class of type-1.5 superconducting nanowire single photon detectors (SNSPDs) based on two bandgap superconductors with high transition temperatures such as MgB2 (Tc ~38.6K). We show that vortex-vortex interactions in two component condensates lead to a unique operating regime where single photons can seed multiple vortices within a hotspot. We also show that dark counts are suppressed in the type-1.5 regime compared to the widely studied type-2 SNSPDs. Our work opens the door for exploring the unique vortex physics of two-gap superconductors for quantum device applications.
@article{arxiv.2507.01240,
title = {Type-1.5 SNSPD: Interacting vortex theory of two bandgap superconducting single photon detectors},
author = {Leif Bauer and Daien He and Sathwik Bharadwaj and Shunshun Liu and Prasanna V. Balachandran and Zubin Jacob},
journal= {arXiv preprint arXiv:2507.01240},
year = {2025}
}