Microwave cavity searches

Abstract

This chapter will cover the search for dark matter axions based on microwave cavity experiments proposed by Pierre Sikivie. We will start with a brief overview of halo dark matter and the axion as a candidate. The principle of resonant conversion of axions in an external magnetic field will be described as well as practical considerations in optimizing the experiment as a signal-to-noise problem. A major focus of this chapter will be the two complementary strategies for ultra-low noise detection of the microwave photons -the "photon-as-wave" approach (i.e., conventional heterojunction amplifiers and soon to be quantum-limited SQUID devices), and the "photon-as-particle" approach (i.e., Rydberg-atom single-quantum detection). Experimental results will be presented; these experiments have already reached well into the range of sensitivity to exclude plausible axion models, for limited ranges of mass. The chapter will conclude with a discussion of future plans and challenges for the microwave cavity experiment. © 2008 Springer-Verlag Berlin Heidelberg.