Superconducting noise bolometer with microwave bias and readout for array applications

TL;DR

This paper introduces a superconducting noise bolometer designed for terahertz detection, featuring microwave bias and readout, suitable for large arrays with high sensitivity and operation above 1 K.

Contribution

It presents a novel superconducting noise bolometer with microwave bias/readout for array applications, demonstrating feasibility and near-expected sensitivity at 4.2 K.

Findings

Achieved noise equivalent power of approximately 3×10⁻¹² W/√Hz.

Operates effectively at 4.2 K with a 5.6 GHz bias frequency.

Feasibility confirmed with a proof-of-concept device on Nb film.

Abstract

We present a superconducting noise bolometer for terahertz radiation, which is suitable for large-format arrays. It is based on an antenna-coupled superconducting micro-bridge embedded in a high-quality factor superconducting resonator for a microwave bias and readout with frequency-division multiplexing in the GHz range. The micro-bridge is kept below its critical temperature and biased with a microwave current of slightly lower amplitude than the critical current of the micro-bridge. The response of the detector is the rate of superconducting fluctuations, which depends exponentially on the concentration of quasiparticles in the micro-bridge. Excess quasiparticles are generated by an incident THz signal. Since the quasiparticle lifetime increases exponentially at lower operation temperature, the noise equivalent power rapidly decreases. This approach allows for large arrays of noise bolometers operating above 1 K with sensitivity, limited by 300-K background noise. Moreover, the response of the bolometer always dominates the noise of the readout due to relatively large amplitude of the bias current. We performed a feasibility study on a proof-of-concept device with a ${1.0\times 0.5 \rm \mu m^{2}}$ micro-bridge from a 9-nm thin Nb film on a sapphire substrate. Having a critical temperature of 5.8 K, it operates at 4.2 K and is biased at the frequency 5.6 GHz. For the quasioptical input at 0.65 THz, we measured the noise equivalent power ${\approx 3\times 10^{-12}\rm W/\sqrt Hz}$ , which is close to expectations for this particular device in the noise-response regime.