  The axion, a hypothetical elementary pseudoscalar, is expected to solve the
strong CP problem of QCD and is also a promising candidate for dark matter. The
most sensitive axion search experiments operate at millikelvin temperatures and
hence rely on instrumentation that carries signals from a system at cryogenic
temperatures to room temperature instrumentation. One of the biggest limiting
factors affecting the parameter scanning speed of these detectors is the noise
added by the components in the signal detection chain. Since the first
amplifier in the chain limits the minimum noise, low-noise amplification is of
paramount importance. This paper reports on the operation of a flux-driven
Josephson parametric amplifier (JPA) operating at around 2.3 GHz with added
noise approaching the quantum limit. The JPA was employed as a first stage
amplifier in an experimental setting similar to the ones used in haloscope
axion detectors. By operating the JPA at a gain of 19 dB and cascading it with
two cryogenic amplifiers operating at 4 K, noise temperatures as low as 120 mK
were achieved for the whole signal detection chain.
