Robust Performance of Superconducting Nanowire Single Photon Detectors under High Magnetic Fields*

Superconducting nanowire single photon detectors (SNSPDs) offer high-quantum-efficiency and low-dark-count single photon detection. For quantum applications, operation may require high magnetic fields if integrated with a spin-based device. Here, we explore the magnetic field dependence of amorphous SNSPDs, determining they are robust up to ±6T with a negligible dark count rate and unchanged quantum efficiency at operation bias currents. However, the maximum bias current is suppressed asymmetrically under opposing fields. The asymmetric dark count origins are under investigation, with additional experiments under perpendicular fields using a milliKelvin scanning confocal microscope. This enables near-diffraction limited resolution of the incident light on the SNSPD, allowing additional study of the position dependence of the SNSPD readout waveforms. Together, these measurements will provide a fundamental improvement in our understanding of the material constraints on SNSPDs.