Fermions from Cold Atoms to Neutron Stars:
Benchmarking the Many-Body Problem

March 14 – May 20, 2011

This program is now complete. Much of the information is summarized on the wiki or in the online talks:

• Wikispace Website:

  This wiki is still in progress and only open to program participants: if you have a scientific interest in the program and would like to contribute to the discussion, please contact Michael M^cNeil Forbes. Once finalized, the wiki will be opened to the public and a link posted here.

• Talks Online:

  Here you will find many of the talks as both podcasts and as static pdf (some ppt) files.

• Obtain an INT preprint number:

  Program participants: please obtain a preprint number for any work related to your experience in the program. This is useful to us even if retroactive: if you have put work on the arXiv, you can still generate a preprint number and add this as a "Report Number" without generating a new version.

• Friends of the INT:

  Please consider making a tax-deductible donation to help support coffee, cookies, and other amenities at the INT that do not qualify for DOE funding.

Overview

The goal of this program is to identify a set of reliable techniques for studying complex behaviors – both static and dynamic – of fermionic many-body systems. The program will:

• Bring together experimentalists and theorists to coherently advance the field, solve present problems, and set an agenda for future many-body studies.
• Make accessible a set of useful tools and models that have been quantitatively benchmarked against experiment and ab initio calculations.

This 9-week program will consist of solicited lectures intermixed with presentations of new results, with ample time for collaboration and directed discussions. A short but intensive experimental symposium will be held at the end of the program May 16^th to May 20^th (2011) including a moderated discussion to directly address questions posed during the longer program. The goal here is to address issues such as:

• How can theory help the experiments? (e.g. What needs to be calculated? Suggestions for new measurement techniques.)
• What are the current and projected capabilities of the experiments?
• What quantities could be measured to efficiently test various theories (including required error and confidence levels)?
• How can results about cold atoms be most effectively used in other systems?

Background

The study of cold fermionic atoms impacts many fields of physics, and the ability to control most aspects of these systems – especially the interaction strength and trapping potentials – has led to an explosion of interest in the universal properties of ultra-cold atomic gases.

Experimental and theoretical studies have led to the fundamental result that cold atoms provide us with the most strongly paired environment in the universe: cold atoms at unitarity have gaps which are of the order of the Fermi energy, leading to the highest relative critical temperatures in any realizable system. They exhibit a richness of phenomena and phases, and exhibit novel properties found in many condensed-matter systems.

The relevance of this physics bridges many orders of magnitude to nuclear and astrophysics. There is a direct connection with dilute neutron matter in neutron stars, and many indirect connections with nuclei, high-density quark matter, the quark-gluon plasma, AdS/CFT, and other quantum field theories.

Despite the broad applicability of the strongly interacting Fermi gas, only a handful of properties have been directly calculated or measured – generally confirming expected properties. However, it is becoming evident that new features await discovery and elucidation, including a pseudogap similar to that found in high-temperature superconductors, exotic superfluid phases such as the FFLO supersolids, p-wave or f-wave superfluidity (similar to liquid ³He), and time-dependent phenomena such as vortex dynamics and quantum turbulence.

A reason for the limited results is that, despite the apparent simplicity of the relevant Hamiltonian, the unitary regime admits no consistent perturbative expansion. For definitive results, one is restricted to costly ab initio calculations for small systems, or to experiments. To theoretically access systems of interest, various models must be employed, since the ubiquitous but simplistic mean-field techniques are no longer accurate to within the precision of experiments and more elaborate calculations.

The primary goal of this program, is to collect, develop, and benchmark a set of practical tools for studying fermionic many-body systems, and to set an agenda for testing these tools. Such a focused theoretical effort would help in singling out the most relevant observables to be measured and calculated, giving clear guidance to the experimental and ab initio efforts.