A SQUID-based microwave cavity search for dark-matter axions

TL;DR

The first result from such an axion search using a superconducting first-stage amplifier (SQUID) replacing a conventional GaAs field-effect transistor amplifier is reported, setting the stage for a definitive axions search utilizing near quantum-limited SQUID amplifiers.

Abstract

Axions in the micro eV mass range are a plausible cold dark matter candidate and may be detected by their conversion into microwave photons in a resonant cavity immersed in a static magnetic field. The first result from such an axion search using a superconducting first-stage amplifier (SQUID) is reported. The SQUID amplifier, replacing a conventional GaAs field-effect transistor amplifier, successfully reached axion-photon coupling sensitivity in the band set by present axion models and sets the stage for a definitive axion search utilizing near quantum-limited SQUID amplifiers.

Figures (5)

• Figure 1: Schematic of ADMX experiment. The lower left-hand sweep oscillator, which is weakly coupled to the cavity, determines the resonant frequency of the TM$_{010}$ mode, while the upper left-hand oscillator allows for a reflection check in order to critically couple the signal antenna to the cavity.
• Figure 2: Schematic of a microstrip SQUID amplifier.
• Figure 3: Noise temperature of two representative SQUID amplifiers (with resonant frequency f) as a function of physical temperature. Dashed line indicates $T_Q$, the quantum noise temperature at $\approx$ 700 MHz. Dotted line has unity slope, indicating that $T_A \propto T$ in the classical regime.
• Figure 4: Dark matter axion signals simulated with Monte Carlo and imposed on real data for two dark matter axion distribution models (masses arbitrarily chosen).
• Figure 5: Axion-photon coupling excluded at the 90% confidence level assuming a local dark matter density of 0.45 $\mathrm{GeV/cm^3}$ for two dark matter distribution models. The shaded region corresponds to the range of the axion photon coupling models discussed in PhysRevD.58.055006.