A distributed electrical model for superconducting nanowire single photon detectors

TL;DR

This paper introduces a distributed transmission line model for superconducting nanowire single photon detectors, revealing how nanowire geometry influences output signals and emphasizing the importance of microwave design for improved performance.

Contribution

The paper develops a novel distributed model for SNSPDs that accounts for nanowire length and geometry, enhancing understanding of their output dynamics and design considerations.

Findings

Distributed model matches experimental results

Nanowire behaves as a transmission line affecting pulse shape

Impedance matching improves detector output

Abstract

To analyze the switching dynamics and output performance of a superconducting nanowire single photon detector (SNSPD), the nanowire is usually modelled as an inductor in series with a time-varying resistor induced by absorption of a photon. Our recent experimental results show that, due to the effect of kinetic inductance, for a SNSPD made of a nanowire of sufficient length, its geometry length can be comparable to or even longer than the effective wavelength of frequencies contained in the output pulse. In other words, a superconducting nanowire can behave as a distributed transmission line so that the readout pulse depends on the photon detection location and the transmission line properties of the nanowire. Here, we develop a distributed model for a superconducting nanowire and apply it to simulate the output performance of a long nanowire designed into a coplanar waveguide. We compare this coplanar waveguide geometry to a conventional meander nanowire geometry. The simulation results agree well with our experimental observations. With this distributed model, we discussed the importance of microwave design of a nanowire and how impedance matching can affect the output pulse shape. We also discuss how the distributed model affects the growth and decay of the photon-triggered resistive hotspot.