Axion Search with Q & A Experiment
  Dark matter is a focused issue in galactic evolution and cosmology. Axion is
a viable particle candidate for dark matter. Its interaction with photon is an
effective way to detect it, e.g., pseudoscalar-photon interaction will generate
vacuum dichroism in a magnetic field. Motivated to measure the QED vacuum
birefringence and to detect pseudoscalar-photon interaction, we started to
build up the Q & A experiment (QED [Quantum Electrodynamics] and Axion
experiment) in 1994. In this talk, we first give a brief historical account of
planet hunting and dark matter evidence. We then review our 3.5 m Fabry-Perot
interferometer together with our results of measuring vacuum dichroism and
gaseous Cotton-Mouton effects. Our first results give (-0.2 $\pm$ 2.8) $\times$
10$^{-13}$ rad/pass, at 2.3 T with 18,700 passes through a 0.6 m long magnet,
for vacuum dichroism measurement. We are upgrading our interferometer to 7 m
arm-length with a new 1.8 m 2.3 T permanent magnet capable of rotation up to 13
cycles per second. We aim at 10 nrad/Hz$^{1/2}$ optical sensitivity with 532 nm
cavity finesse around 100,000. When achieved, vacuum dichroism would be
measured to 8.6 $\times$ 10$^{-17}$ rad/pass in about 50 days, and QED
birefringence would be measured to 28 %.
