Coincidence Detection of Double-Layered Current-Biased Kinetic Inductance Detectors Using a 20 ps Pulsed Laser

We demonstrated the operation of double-layered current-biased kinetic inductance detectors (CB-KIDs) made of Nb by irradiating pulsed laser. A Nb-based CB-KID operates at temperatures appreciably lower than a superconducting transition temperature Tc because it senses a time derivative of kinetic inductance dLk/dt in a Nb meanderline. We fabricated double-layered meanderlines to detect a coordinate. Two meanderlines of 40 nm thickness and 1 μm line width have an orthogonal configuration with each other. We deposited a 10B layer of thickness 300 nm to insulate between two Nb meanderlines. The total area of the meanderlines is 10.4 mm × 10.4 mm at the center of chip with the size of 22 mm × 22 mm. The pulse width and wavelength of pulsed laser is 20 ps and 1547 nm, respectively. We obtained the output signals from two CB-KIDs simultaneously by irradiating a focused pulsed laser. The response time is a few tens ns, and operating margin is 300-350 μA.