Numerical analysis of detection-mechanism models of superconducting nanowire single-photon detector

Abstract

The microscopic mechanism of photon detection in superconducting nanowire single-photon detectors is still under debate. We present a simple but powerful theoretical model that allows us to identify essential differences between competing detection mechanisms. The model is based on quasi-particle multiplication and diffusion after the absorption of a photon. We then use the calculated spatial and temporal evolution of this quasi-particle cloud to determine detection criteria of three distinct detection mechanisms, based on the formation of a normal conducting spot, the reduction of the effective depairing critical current below the bias current, and a vortex-crossing scenario, respectively. All our calculations as well as a comparison to experimental data strongly support the vortex-crossing detection mechanism by which vortices and antivortices enter the superconducting strip from the edges and subsequently traverse it thereby triggering the detectable normal conducting domain. These results may therefore help to reveal the microscopic mechanism responsible for the detection of photons in superconducting nanowires. V C 2013 AIP Publishing LLC.

Optically probing the detection mechanism in a molybdenum silicide superconducting nanowire single-photon detector

“…For 220 nm-wide NbN SNSPDs made from nanobridges, and also with nanodetectors and meanders, the energy-current relation was found to be linear in the range of 0.75-8.26 eV using the quantum detector tomography (QDT). 24 A result consistent with this was found for TaN detectors 37 and for a series of NbN meanders of varying widths. 38 Nevertheless, a nonlinear behaviour for NbN meanders probed with a filtered black body light source was later observed in the 0.5-2.75 eV range 28 by using the two probability thresholds g ¼ 50% and 90% of the normalised PCR.…”

Detection mechanism of superconducting nanowire single-photon detectors

“…The background of thermally excited QPs is neglected. This results in the coupled differential equations [105] ∂C e ( r, t) ∂t…”

“…In [105] numerical results were compared with implementations of the normal-core hotspot model and the diffusion-based hotspot model within the same framework. The authors found clear indications that their new model and the underlying physics would lead to the entry of a vortex and thus the trigger of a normal domain before either of the other models predicts a detection event.…”

“…Its weak point is the assumption that the local velocity of the superconducting condensate is uniform across the strip. A model was proposed [105], with some later corrections [106], that combines the generation and diffusion of QPs after photon absorption with the formation of the normal-conducting cross-section due to vortices overcoming the edge-barrier for vortex entry. It turns out that a realistic description of the underlying processes can only be obtained with numerical methods.…”

Position-Dependent Local Detection Efficiency in a Nanowire Superconducting Single-Photon Detector

“…SSPDs have high efficiency, low jitter, low dark count rate and fast reset time [2], and are therefore a key technology for, among others, quantum key distribution Although progress has been made recently, the underlying physical mechanism responsible for photon detection on the nanoscale is still under active investigation. A combination of theory [6,7], experiments [8][9][10] and simulations [11,12] on NbN SSPDs indicates that the absorption of a photon destroys Cooper pairs in the superconductor and creates a localized cloud of quasiparticles that diverts current across the wire. This makes the wire susceptible to the entry of a superconducting vortex from the edge of the wire.…”