  We propose a dual-path interferometry amplification configuration in cavity
axion dark matter searches. We show quantum-mechanically that in a
low-temperature cavity permeated by a magnetic field, the single axion-photon
conversion rate is enhanced by the cavity quality factor $Q$ and quantitatively
larger than the classical result by a factor $\pi/2$. Under modern cryogenic
conditions, thermal photons in the cavity are negligible; thus, the axion
cavity can be considered a quantum device emitting single photons with temporal
separations. This differs from the classical picture in which axions transition
in batches and the converted energy accumulates in the electromagnetic field
inside the cavity. It reveals a possibility for the axion cavity experiment to
handle the signal sensitivity at the quantum level, e.g., cross-power and
second-order correlation measurements. The correlation of photon field
quadratures in the amplification chain within current technology enhances the
signal-to-noise ratio compared with a single-path amplification scheme based on
a high electronic mobility transistor amplifier or Josephson Parametric
Amplifiers (JPAs). In particular, it is useful to combine the dual-path
interferometry scheme with other techniques, e.g., JPAs, to overcome the
inevitable microwave signal insertion loss (normally $\sim-3\,$dB) in the
channels between the cavity and the quantum-limited amplifiers. This
enhancement would greatly reduce the signal scanning time to improve the
sensitivity of the axion-photon coupling. In addition, the second-order
correlation function measurement in the dual-path scheme can provide an
additional verification of whether the candidate signals are axion converted or
other noises.
