Development of Lumped Element Kinetic Inductance Detectors for phonon and photon detections

We present recent developments of our phonon and photon detections using Lumped Element Kinetic Inductance Detectors (LEKIDs). Photons or phonons incident on super-conducting material break Copper-pairs and change its kinetic inductance. If the superconductor is in a form of a resonator, the resonant frequency shifts depending on the deposited energy of the incident phonon or photon. We have been developing arrays of such detectors with different frequencies, and multiplex readouts in the frequency domain. We have optimized positions of resonators minimizing cross-talks between the neighboring resonators using simulation, and were able to detect phonons created in the substrate by irradiating α particles. We have also successfully counted photons incident on LEKIDs by a laser. We discuss possible future applications using LEKIDs. as well.