Getting down to liquid helium temperatures (4K) may be fairly straight forward, but cooling below that requires taking advantage of quantum phenomena. In this video Associate Professor Andrea Morello from the University of New South Wales explains how 'zeropoint motion' makes it possible to use Helium3 and Helium4 in a dilution fridge to get down to only thousandths of degrees above absolute zero.
It is this technique which is used to cool the MiniGrail at Leiden so that it can act as a gravitational wave antenna.
For more on Dr. Morello, see: http://bit.ly/17wZ7lt