Four-Channel Current-Biased Kinetic Inductance Detectors Using MgB$_2$ Nanowires for Sensing Pulsed Laser Irradiation

Abstract

We recently proposed the idea of a novel sort of superconducting detector, i.e., a current-biased kinetic inductance detector (CB-KID). This detector is different from a current-biased transition edge detector studied previously, and is able to sense a change in kinetic inductance $L_k$ given by $L_{k} = \Lambda _{k}l/S = m_{s}l/n_{s}{q_{s}}^{2}S$ ($\Lambda _{k}$; kinetic inductivity, $m_s$; mass of Cooper pair, $n_s$; density of Cooper pairs, $q_s$; charge of Cooper pair, $l$; length of device, $S$; cross sectional area) under a constant dc bias current $I_b$. In the present work, we first extend this idea to construct a multi-channel CB-KIDs array made of 200-nm-thick MgB$_2$ thin-film meanderline with 3-$\upmu$m thin wire. We succeeded in observing clear signals for imaging from the four-channel CB-KIDs at 4 K by irradiating focused pulsed laser. A scanning laser spot can be achieved by an XYZ piezo-driven stage and an optical fiber with an aspheric focused lens. We can see typical signals from all 4 channels at 4 K, and obtain the positional dependence of the signal as the contour in XY plane. Our CB-KIDs can be used as neutron detectors by utilizing energy released from a nuclear reaction between $^{10}$B and cold neutron.