Spatial dependence of output pulse delay in a niobium nitride nanowire superconducting single-photon detector

We report on the position-dependent variation in output pulse timing across a superconducting single-photon detector. Our device consists of a single niobium nitride nanowire meander (100 nm width, 4 nm film thickness, 2 mm length). We use a confocal microscope configuration (full width at half maximum-spot size 1.3 μm at 1550 nm wavelength) and a femtosecond laser to study local variations in detection efficiency and output pulse timing. Pulse delays of up to 50 ps across the device correlate to local detection efficiency and resistance variations. This study indicates an underlying mechanism for timing jitter in superconducting nanowire devices.