Hunting for axions with the measurements of photon's birefringence

Axions are the hypothetical elementary particles with their small masses and tiny interactions to matter sectors, and they are known as promising candidates for the dark sector in our universe. Axions generically couple to the photon via the chiral anomaly effect and differentiate the phase velocities between two circularly-polarized photons, which leads to a rotation of the photon's polarization plane called the birefringence effect. In this talk, I will present a recent development of cosmic axion background search with the observations of photon's birefringence.