  Microwave Kinetic Inductance Detectors (MKIDs) have great potential for large
very sensitive detector arrays for use in, for example, sub-mm imaging. Being
intrinsically readout in the frequency domain, they are particularly suited for
frequency domain multiplexing allowing $\sim$1000s of devices to be readout
with one pair of coaxial cables. However, this moves the complexity of the
detector from the cryogenics to the warm electronics. We present here the
concept and experimental demonstration of the use of Fast Fourier Transform
Spectrometer (FFTS) readout, showing no deterioration of the noise performance
compared to low noise analog mixing while allowing high multiplexing ratios.

Instrumentation and Methods for Astrophysics;Superconductivity