Searches for Cosmological Axions

What constitutes the dark matter is one of the premier questions in 
science today. A leading candidate is a very light axion. As shown by 
Sikivie, halo axions may be detected by their coherent conversion to 
microwave photons in a high-Q cavity permeated by a strong magnetic 
field. A collaboration from LLNL, Florida, Berkeley and NRAO has 
developed the world's quietest radio receiver for this search and has 
achieved sensitivity well into the range of axion models. The 
Berkeley group has developed a breakthrough technology, 
near-quantum-limited SQUID amplifiers, which will reduce the noise 
temperature of the experiment by a factor of 30, thus enabling a 
truly definitive search.  A similar effort in Kyoto is attempting to 
implement a Rydberg-atom single-quantum detector as the back end of 
the Sikivie microwave cavity experiment, that could evade the quantum 
limit entirely.