  Detecting spatial and temporal information of individual photons by using
single-photon-detector (SPD) arrays is critical to applications in
spectroscopy, communication, biological imaging, astronomical observation, and
quantum-information processing. Among the current SPDs1,detectors based on
superconducting nanowires have outstanding performance2, but are limited in
their ability to be integrated into large scale arrays due to the engineering
difficulty of high-bandwidth cryogenic electronic readout3-8. Here, we address
this problem by demonstrating a scalable single-photon imager using a single
continuous photon-sensitive superconducting nanowire microwave-plasmon
transmission line. By appropriately designing the nanowire's local
electromagnetic environment so that the nanowire guides microwave plasmons, the
propagating voltages signals generated by a photon-detection event were slowed
down to ~ 2% of the speed of light. As a result, the time difference between
arrivals of the signals at the two ends of the nanowire naturally encoded the
position and time of absorption of the photon. Thus, with only two readout
lines, we demonstrated that a 19.7-mm-long nanowire meandered across an area of
286 {\mu}m * 193 {\mu}m was capable of resolving ~590 effective pixels while
simultaneously recording the arrival times of photons with a temporal
resolution of 50 ps. The nanowire imager presents a scalable approach to
realizing high-resolution photon imaging in time and space.
