The axion was originally postulated to explain why the strong interactions conserve parity (P) and the product of parity with charge conjugation (CP). It has been shown that, for a range of values of the axion mass in the neighborhood of 10^-6 to 10^-5 eV/c², axions are the most abundant form of matter in the universe. They are, in fact, an excellent candidate for being the constituent matter of the dark halos that envelop galaxies.

An experiment that attempts to detect Milky Way halo axions has been built at Livermore National Laboratory and has operated for 4 years now. The aim of the experiment is to observe the conversion of axions to microwave photons in an electromagnetic cavity which is tuned to the axion mass and which is permeated by a larger static magnetic field. The experiment has set the first significant limits on the axion density for part of the interesting mass range.

An upgrade to this apparatus adds SQUID amplifiers to the front-end electronics of the experiment, with the potential to improve the noise temperature by more than an order of magnitude.

Now, I take you to the ADMX axion page.