Quest towards ultimate performance in superconducting nanowire single photon detectors

In 2007, superconducting nanowire single photon detectors （SSPD or SNSPD） [ 1 ] made an outstanding impact in the field of quantum information technology by demonstrating quan- tum key distribution （QKD） over a 200-kin optical fiber with a 42-dB optical loss using a practical SNSPD system [2]. This successful demonstration was realized thanks to its extremely low dark count rate （DCR） of a few Hz and short timing jitter of 60 ps, while the system detection efficiency （SDE） showed a poor value of 0.7% at a wavelength of 1550 nm.