Macroscopic quantum states at ultra-low temperature

Author(s): William Halperin

The reach of quantum mechanics to condensed matter phenomena on a macroscopic scale has resulted from engineering capability to maintain ultra-low temperatures for ultra-long times. Here I will discuss recent results on the quantum states of superfl uid 3He and their connection to topological superconductivity. We have learned how to control the fundamental symmetries of the superfl uid, including time reversal symmetry, mirror symmetry like that of DNA. Interestingly, new phases with these symmetries can be induced by imbibing the superfl uid into high porosity silica aerogel. The production of these gels and their wide range of applications are by themselves very intriguing. However, in our application we grow 98% porous aerogels with global, uniaxial anisotropy. It is the anisotropy that controls the symmetry of the order parameters of the quantum states of the superfl uid, including magnetic superfl uid states, liquid crystal superfl uid states, and states with chiral symmetry. We show that the same physics is evident in the topological superconductor, UPt3. It seems like a chance of nature that the lightest and heaviest superconductors can share a commonality in their unconventional quantum mechanical behaviour.