  Recent progress in the development of superconducting nanowire single-photon
detectors (SNSPD) has delivered ex-cellent performance, and their increased
adoption has had a great impact on a range of applications. One of the key
characteristic of SNSPDs is their detection rate, which is typically higher
than other types of free-running single-photondetectors. The maximum achievable
rate is limited by the detector recovery time after a detection, which itself
is linked to the superconducting material properties and to the geometry of the
meandered SNSPD. Arrays of detectors biased individually can be used to solve
this issue, but this approach significantly increases both the thermal load in
the cryo-stat and the need for time processing of the many signals, and this
scales unfavorably with a large number of detectors. One potential scalable
approach to increase the detection rate of individual detectors further is
based on parallelizing smaller meander sections. In this way, a single
detection temporarily disables only one subsection of the whole active area,
thereby leaving the overall detection efficiency mostly unaffected. In practice
however, cross-talk between parallel nanowires typically leads to latching,
which prevents high detection rates. Here we show how this problem can be
avoided through a careful design of the whole SNSPD structure. Using the same
electronic readout as with conventional SNSPDs and a single coaxial line, we
demonstrate detection rates over 200 MHz without any latching, and a
fibre-coupled SDE as high as 77%, and more than 50% average SDE per photon at
50 MHz detection rate under continuous wave illumination.

Applied Physics;Quantum Physics