Quantum sensing in axion dark matter search

Cosmological evidence shows the presence in the universe of more mass than what can be inferred from luminosity measurements. This excess of mass, known as \gls{DM}, forms halos around the galaxies. It is still unknown what DM is made of. Axions are hypothetical particles among leading DM candidates. Experimental axion search requires detectors at the ultimate level of sensitivity allowed by quantum mechanics. Haloscopes are detectors employed in axion search made of a resonant cavity immersed in a strong magnetic field. With today’s leading technology based on quantum-limited linear amplifiers, the sensitivity is fundamentally limited by vacuum fluctuations of the cavity field and it may take centuries to probe the most plausible parameter space. Such quantum limits can be overcome if microwave photon counting is adopted. The microwave domain detection of individual photons is a challenging task because the photon energy is roughly five orders of magnitude lower than at optical frequencies. Very recently a practical single microwave photon detectors have been introduced in the field of quantum information science. The low dark count rate, tunability, and the continuous operation of this device will be exploited to demonstrate a quantum-enhanced search of axions at the QUAX haloscope.