Stepping closer to pulsed single microwave photon detectors for axions search

TL;DR

This paper explores two superconducting device approaches for detecting single microwave photons, aiming to improve axion search sensitivity by achieving ultra-low dark counts and high photon detection efficiency.

Contribution

It introduces and tests two novel superconducting device configurations for pulsed microwave photon detection relevant to axion searches.

Findings

Device with Josephson junction detects ~10 photons at 8 GHz

Resonator coupled with qubit shows modulation of resonance frequency up to 4 MHz

Both approaches have potential for single photon sensitivity after optimization

Abstract

Axions detection requires the ultimate sensitivity down to the single photon limit. In the microwave region this corresponds to energies in the yJ range. This extreme sensitivity has to be combined with an extremely low dark count rate, since the probability of axions conversion into microwave photons is supposed to be very low. To face this complicated task, we followed two promising approaches that both rely on the use of superconducting devices based on the Josephson effect. The first one is to use a single Josephson junction (JJ) as a switching detector (i.e. exploiting the superconducting to normal state transition in presence of microwave photons). We designed a device composed of a coplanar waveguide terminated on a current biased Josephson junction. We tested its efficiency to pulsed (pulse duration 10 ns) microwave signals, since this configuration is closer to an actual axions search experiment. We show how our device is able to reach detection capability of the order of 10 photons with frequency 8 GHz. The second approach is based on an intrinsically quantum device formed by two resonators coupled only via a superconducting qubit network (SQN). This approach relies on quantum nondemolition measurements of the resonator photons. We show that injecting RF power into the resonator, the frequency position of the resonant drop in the transmission coefficient (S21) can be modulated up to 4 MHz. We anticipate that, once optimized, both the devices have the potential to reach single photon sensitivity.