  In this work, we present a novel device that is a combination of a
superconducting nanowire single-photon detector and a superconducting
multi-level memory. We show that these devices can be used to count the number
of detections through single-photon to single-flux conversion. Electrical
characterization of the memory properties demonstrates single-flux quantum
(SFQ) separated states. Optical measurements using attenuated laser pulses with
different mean photon number, pulse energies and repetition rates are shown to
differentiate single-photon detection from other possible phenomena, such as
multi-photon detection and thermal activation. Finally, different geometries
and material stacks to improve device performance, as well as arraying methods
are discussed.
