Superconducting Nanowire Single-Photon Detectors

Abstract

Single-photon-detector arrays can provide unparalleled performance and detailed information in applications that require precise timing and single photon sensitivity. Such arrays have been demonstrated using a number of single-photon-detector technologies, but the high performance of superconducting nanowire single photon detectors (SNSPDs) and the unavoidable overhead of cryogenic cooling make SNSPDs particularly likely to be used in applications that require detectors with the highest performance available. These applications are also the most likely to benefit from and fully utilize the large amount of information and performance advantages provided by a single-photon-detector array. Although the performance advantages of individual superconducting nanowire single photon detectors (SNSPDs) have been investigated since their first demonstration in 2001, the advantages gained by building arrays of multiple SNSPDs may be even more unique among single photon detector technologies. First, the simplicity and nanoscale dimensions of these detectors make it possible to easily operate multiple elements and to closely space these elements such that the active area of an array is essentially identical to that of a single element. This ability to eliminate seam-loss between elements, as well as the performance advantages gained by using multiple smaller elements, makes the multi-element approach an attractive way to increase the general detector performance (detection efficiency and maximum counting rate) as well as to provide new capabilities (photon-number, spatial, and spectral resolution). Additionally, in contrast to semiconductor-based single-photon detectors, SNSPDs have a negligible probability of spontaneously emitting photons during the detection process, eliminating a potential source of crosstalk between array elements. However, the SNSPD can be susceptible to other forms of crosstalk, such as thermal or electromagnetic interactions between elements, so it was important to investigate the operation and limitations of multi-element SNSPDs. This thesis will introduce the concept of a multi-element SNSPD with a continuous active area and will investigate its performance advantages, its potential drawbacks and finally its application to intensity correlation measurements.

Spatially dependent sensitivity of superconducting meanders as single-photon detectors

“…Dissipative crossing of such vortices, which hop over the edge barrier, or are created due to the unbinding of thermally activated vortex-antivortex pairs, provides a good description of the experiment [10]. This vortex-based mechanism was also shown to be the dominating origin for dark counts [11,12,14], which leads to decoherence in the photon detection process.To increase the efficiency of the photon counting, detectors are usually fabricated as a meandering superconducting wire [3]. However, these structures are vulnerable to edge imperfections [3], which significantly reduce the photon counting rate.…”

“…Moreover, the critical current in these systems is mostly determined by sharp inner corners where the supercurrent density is maximal due to current crowding [15,16]. While the appearance of edge imperfections can be reduced by present day technology [3], the effect of current crowding in such meandering geometries still demands further investigations.In this work we therefore study the effect of the turns of a meandering superconducting stripe on the response to a single-photon absorption event. Counterintuitive to many, we reveal that the current crowding at meandering turns does not facilitate dissipative vortex crossings upon the photon impact.…”

“…To increase the efficiency of the photon counting, detectors are usually fabricated as a meandering superconducting wire [3]. However, these structures are vulnerable to edge imperfections [3], which significantly reduce the photon counting rate.…”

“…Superconducting current-carrying thin-film stripes have recently received a revival of interest due to their promising application for single-photon detection [1] with a high maximum count rate, broadband sensitivity, fast response time and low dark counts [2][3][4]. The singlephoton absorption event leads to the formation of a nonequilibrium "hotspot" with suppressed superconductivity, the area of which grows in time, forming a normal belt across the strip [5].…”

“…To increase the efficiency of the photon counting, detectors are usually fabricated as a meandering superconducting wire [3]. However, these structures are vulnerable to edge imperfections [3], which significantly reduce the photon counting rate. Moreover, the critical current in these systems is mostly determined by sharp inner corners where the supercurrent density is maximal due to current crowding [15,16].…”