High quantum efficiency and low dark count rate in multi-layer superconducting nanowire single-photon detectors

Abstract

In this paper, we theoretically show that a multi-layer superconducting nanowire single-photon detector (SNSPD) is capable of approaching characteristics of an ideal SNSPD in terms of the quantum efficiency, dark count, and band-width. A multi-layer structure improves the performance in two ways. First, the potential barrier for thermally activated vortex crossing, which is the major source of dark counts and the reduction of the critical current in SNSPDs is elevated. In a multi-layer SNSPD, a vortex is made of 2D-pancake vortices that form a stack. It will be shown that the stack of pancake vortices effectively experiences a larger potential barrier compared to a vortex in a single-layer SNSPD. This leads to an increase in the experimental critical current as well as significant decrease in the dark count rate. In consequence, an increase in the quantum efficiency for photons of the same energy or an increase in the sensitivity to photons of lower energy is achieved. Second, a multi-layer structure improves the efficiency of single-photon absorption by increasing the effective optical thickness without compromising the single-photon sensitivity.

Unconventional Applications of Superconducting Nanowire Single Photon Detectors

“…Another technique, which is not yet standard in SNSPD applications, and could find another uses in the future is using multi-layer devices, with patterned superconducting layers separated by dielectric spacing layers [ 111 , 112 , 113 , 114 ] as shown in Figure 3 . As the most popular superconductors used for SNSPD fabrication have reflectivity of more than 0.5 in most of the interesting wavelength range [ 115 ], one requires to integrate them into photonic cavities or integrate anti-reflective coatings, which turn them into inherently narrowband detectors.…”

“…As the most popular superconductors used for SNSPD fabrication have reflectivity of more than 0.5 in most of the interesting wavelength range [ 115 ], one requires to integrate them into photonic cavities or integrate anti-reflective coatings, which turn them into inherently narrowband detectors. This can be alleviated by tuning the thickness of the dielectric spacing layers to increase absorption for different wavelengths in different superconducting layers and effectively making a broadband detector device, as was successfully demonstrated in NbN-based detectors [ 111 , 113 ]. Similar attempts were made using amorphous WSi as the superconducting material [ 112 ], but they didn’t achieve increase of detection efficiency as with the crystalline materials—something that is argued in the work to be due to fabrication defects and insufficiently low reduced working temperature .…”

The potential and challenges of time-resolved single-photon detection based on current-carrying superconducting nanowires

“…Below the Kosterlitz-Thouless topological transition, the vibration of vortex-antivortex pairs and pinned vortices or the thermal activation of magnetic Pearl vortices over the potential barrier will cause dissociation of pairs or vortex entry from one edge, resulting in dark and photon counts. Hence, the thermally excited hopping of magnetic vortices can be obviously affected by the thermal coupling of the superconducting nanowire [15,16]. By increasing the strength of the thermal coupling of the NbN nanowire to the heat sink or using stacked multi-layer pancake SNSPDs, the dark count rate can be significantly suppressed due to the lower obstruction of the vortex movement across the nanowire potential barrier.…”

Dynamics and heat diffusion of Abrikosov’s vortex-antivortex pairs during an annihilation process

“…In practice, mesoscopic superconducting materials have been applied in devices like amplifiers [33], imaging of single magnetic flux quantum (single vortex) [34], single electron [35] and single photon [36][37][38][39] detectors, and the knowledge of the V-AV dynamics in such materials is of great importance to improve specific characteristics to those applications.…”