Large inverse transient phase response of titanium-nitride-based microwave kinetic inductance detectors

Abstract

Following optical pulses (λ=405 nm) on titanium nitride microwave kinetic inductance detectors cooled down at temperatures T≤Tc/20 (Tc≃4.6 K), we observe a large phase-response highlighting two different modes simultaneously that are nevertheless related. The first corresponds to the well-known transition of cooper-pair breaking into quasi-particles, which produces a known phase response. This is immediately followed by a large inverse response lasting several hundreds of microseconds to several milliseconds depending on the temperature. We propose to model this inverse pulse as the thermal perturbation of the superconductor and interaction with a two-level system (TLS) that reduces the dielectric constant, which in turn modifies the capacitance and, therefore, the resonance frequency. The ratio of the TLS responding to the illumination is on the order of that of the area of the inductor to the whole resonator.

Development of MKIDs in the Optical and Near-Infrared Bands for SPIAKID

“…It can be seen from Fig. 5D that energy-resolving power increases a bit as T bath increases, which can be attributed to the increasing signal-to-noise ratio (SNR) and a reduction in the noise of the two-level system [22,23], as indicated in Fig. 5C.…”

Investigation of quasi-particle relaxation in strongly disordered superconductor resonators

“…η tends to increase when T bath increases especially for TiN 2K . One of the possible reasons for the rise of η is due to the presence of the two-level system (TLS) on the interface between the TiN and the sapphire, which absorbs part of the photon energy [19]. As T bath increases, TLS saturates, and then η increases.…”

“…MKIDs in the optical and near-infrared bands are usually high-quality lumped superconducting resonators [7,10,[17][18][19][20] that are made of an interdigitated capacitor (IDC) and a meander. Photons (hω > 2∆) absorbed in the meander break Cooper pairs and generate QPs, recombining into Cooper pairs and emitting phonons within the QP lifetime.…”

“…The 1-photon and the 0-photon responses averaged from the FWHM of the corresponding peak in the pulse statistics of the measured MKID for Popt = 5 dBm. The photon absorption in the meander is obtained by removing the 0-photon event calculated by equation(19). The inset shows the pulse statistics illuminated with two different optical powers.…”

Development of TiN-Based Suspended Meander Kinetic Inductance Detectors (KIDs) for Visible and Near-Infrared Astronomy Applications

“…The first is the readout noise, which is mainly dominated by the first low-noise amplifier in the system. The other is two-level systems (TLS) featured on the interface between the dielectrics and the superconductor [2], which will also reduce the response of the resonator [3].…”