Probing Virtual ALPs by Precision Phase Measurements: Time-Varying
  Magnetic Field Background
  We propose an experimental scheme for detecting the effects of off-shell
axion-like particles (ALPs) through optical cavities. In this proposed
experiment, linearly polarized photons are pumped into an optical cavity where
an external time-dependent magnetic field is present. The magnetic field
mediates an interaction between the cavity photons and ALPs giving rise to a
modification in the phase of the cavity photons. The time-dependent nature of
the external magnetic field prompts a novel amplification effect which
significantly enhances this phase modification. A detection scheme is then
proposed to identify such axion-induced phase shifts. We find that the phase
modification is considerably sensitive to the photon-ALPs coupling constants
$g_{a\gamma\gamma}$ for the range of ALPs mass
$2\times10^{-6}\:\textrm{eV}\leqslant m_a \leqslant
6.3\times10^{-5}\:\textrm{eV}$.
