From cold atoms to quark-gluon plasmas

In 2007 Gordon Baym gave a fascinating talk New States of Quantum Matter which is nicely summarised in a short conference paper. You can watch a 2010 version of the talk here.

Baym discusses similarities of the physics associated with cold atomic gases and quark-gluon plasmas. These similarities occur in spite of the fact that the relevant energy scales in the two systems differ by more than 20 orders of magnitude!

For example, the phase diagram below shows the different phases of a many-body quark system as a function of temperature and chemical potential.
Increasing the chemical potential corresponds to increasing the density. [Remember that for a non-interacting Fermi gas the Fermi energy increases with density].

Note that at "low" temperatures there is a continuous cross-over from a hadronic superconductor [roughly a BEC of paired quarks] to a quark superconductor. Baym points out that some level this is analogous to the BEC-BCS crossover that occurs in ultracold Fermi gases as one tunes the interaction from repulsion to attraction (e.g. via a Feshbach resonance). However, like all analogies this is not perfect. The quark system involves three different "colours" of fermion with different masses, whereas the cold gas one involves two with identical mass. An interesting challenge for the cold atom community is to design the corresponding three fermion system. This has been discussed by Rapp, Zarand, Honerkamp, and Hofstetter  (see the associated Nature Physics News and Views by Frank Wilczek).