Superfluids and Superconductors

The notion that atoms of a given isotope are indistinguishable has profound consequences in the quantum world. For liquids made of identical bosons, indistinguishability forces the particles into a quantum condensate at low temperature, where they all dance in perfect synchrony. Treated gently, such a condensate has no viscosity: once it is set in motion --say around a circular pipe -- flow will persist indefinitely (so long as the fluid is kept sufficiently cold!). John Chalker will discuss how the laws of quantum mechanics lead us from the microscopic world to macroscopic phenomena.

Stephen Blundell will review a theory of superconductivity that was developed in Oxford in the 1930’s by Fritz London. The idea is that under certain conditions quantum coherent effects can become manifest on a large scale. In an effect such as superconductivity, this idea can be put to use in such applications as magnetic resonance imaging, in which a living human patient is inserted inside a quantum coherent wave function. He will explain how coherent effects can be measured in real superconductors.

Superfluids spontaneously break a continuous symmetry linked to the conservation of particle number in a many-body system. Standard lore holds that such symmetries must remain unbroken at any temperature above absolute zero in a two-dimensional material, such as a thin sheet or film, apparently precluding superfluidity in such systems. In this talk, Siddharth Parameswaran will discuss how a topological approach to 2D systems reveal that they can indeed become superfluid, and lead to surprising and beautiful universal results whose implications continue to resonate today — and won its co-creators, David Thouless and Michael Kosterlitz, the 2016 Nobel Prize.