a SCDs of a 55-nm-wide YBCO nanowire measured at 5.4 K for different LED irradiances. Regions I and II (blue) correspond to ground and exited energy states of the nanowire. Region III (red) is the current region, in which switching can only occur by the hotspot effect. Source data are provided as a Source Data file. b Illustration of the interaction of optical photons with the YBCO nanowire. The populated energy level is shown by a red dot. Photon absorption and escape events are indicated by wavy yellow and red arrows, respectively. Collapse of the order parameter after photon absorption is shown by an inclined blue line. The currents I1, I2, and I3 are the same as in Fig. 4e. The current IHS indicates the boundary of the hotspot regime.