Macroscopic Quantum Phenomena

Macroscopic Quantum Phenomena

Quantum physics is generally characterized as the science of the very small, but under certain circumstances quantum effects lead to dramatic changes in the properties of materials on macroscopic scales. ‘Macroscopic’ quantum phenomena involve collective behavior of enormous numbers of interacting quantum particles, and quantitative analysis of many of these systems (like high temperature superconductors) is extremely challenging. Many-body quantum systems are often difficult to handle theoretically, and in some important cases the true nature of the phase diagram is not yet accurately known. One possible path to gain deeper understanding of these incredibly rich physical systems is to engineer a “synthetic” many body quantum system that maps onto a particular system of interest, but has more conveniently tunable properties.

One important advantage to studying quantum states of matter using ultracold atoms is that we can control the interactions between the atoms by varying an externally applied magnetic field.The ability to make the interactions weak or strong, attractive or repulsive, allows us to extract far more information about a given system than when these parameters are not tunable, as is the case with most  “real” condensed matter systems.

Recent Posts

Persistent Currents in a Molecular BEC of Fermions

We have just shown that we can clearly distinguish between a ring with a persistent current flowing around it and a stationary superfluid (molecular BEC of Li-6). The basic procedure is to relax the radial confinement of the atoms in the ring trap in a prescribed way, then suddenly release the atoms completely and allow the cloud to expand for several milliseconds. If there is (quantized) circulation around the ring then we see a hole in the middle of the expanded cloud, because of the phase singularity that must be present in the superfluid.

For comparison, if there is no circulation in the superfluid, then the expanded cloud looks like this:

Detecting the vortex signature in this expanding fermionic superfluid is a little more challenging to do well than in previous experiments with atomic Bose condensates (of e.g. rubidium or sodium). The cloud expands quite rapidly even for small numbers of atoms, because the momentum of the atoms is comparatively high due to degeneracy pressure. We’ve got a handle on this, though and it’s clearly not going to be an obstacle to the experiments we have planned. The images above mostly look noisy due to photon shot noise, and we expect to be able to du much better than this soon.

 

  1. Stirring Beam Installed Comments Off on Stirring Beam Installed
  2. Fermionic Atoms in Ring Lattices Comments Off on Fermionic Atoms in Ring Lattices
  3. Fermionic Lithium in a Ring Trap Comments Off on Fermionic Lithium in a Ring Trap
  4. Evaporation in the “Sheet” Trap Comments Off on Evaporation in the “Sheet” Trap