  The axion particle, a consequence of an elegant hypothesis that resolves the
strong-CP problem of quantum chromodynamics, is a plausible origin for
cosmological dark matter. In searches for axionic dark matter that detect the
conversion of axions to microwave photons, the quantum noise associated with
microwave vacuum fluctuations will soon limit the rate at which parameter space
is searched. Here we show that this noise can be partially overcome either by
squeezing the quantum vacuum using recently developed Josephson parametric
devices, or by using superconducting qubits to count microwave photons. The
recently demonstrated ability of superconducting qubits to make QND
measurements of microwave photons offers great advantages over destructive
photon counting methods such as those using Rydberg atoms.
