Optimizing waveguide-coupled superconducting nanowire single photon detectors for high magnetic fields

Superconducting nanowire single-photon detectors (SNSPDs) compatible with large magnetic fields are crucial for applications in nuclear physics, dark matter detection and color-center-based quantum technologies. SNSPDs show improved photon count rate (PCR) and reduced critical current in magnetic fields. Prior studies focus on saturation current shifts and reducing current crowding in bends, but the impact of nanowire dimensions on these effects remains underexplored. To study the cross-section dependence of PCR and critical current, we fabricated NbTiN SNSPDs between 60 nm and 130 nm wide and between 6 nm and 12 nm thick on Si₃N₄ waveguides and measured them at 1 K in the presence of a magnetic field. We use waveguide-coupled SNSPDs for their simple single-bend geometry and straightforward nanophotonic integration. To support the findings, we use 3D simulations based on time-dependent Ginzburg-Landau (TDGL) equations. Preliminary PCR measurements of narrow SNSPDs show a shift in saturation current toward higher values in magnetic fields. This is unlike the downward shifts reported in the literature for wider nanowire dimensions, highlighting the need for a deeper understanding of the cross-section's influence on PCR characteristics.