Using Ultracold Atoms to Model Nuclei and Neutron Matter
It may seem surprising that a dilute, ultracold atomic gas could share anything in common with nuclei or neutron star matter since the details of their interactions and their absolute energy scales differ so dramatically. Yet when the deBroglie wavelength greatly exceeds the range of interactions and the scattering length is large, universal predictions can be made that apply equally well to both systems. For example, we have observed the Efimov effect, first predicted in the context of nuclear physics, wherein three particles form an infinite geometric sequence of three-body bound states. Our experiments have confirmed this remarkable 40-year-old prediction by observing successive states in the Efimov spectrum of three fermionic lithium atoms and showing that the successive states are related by a universal scale factor. I will also discuss measurements of the universal interaction energy for a strongly-interacting Fermi gas with zero-range interactions that would be relevant to the equation of state for neutron matter at extremely low densities. By recently demonstrating a Fermi system with a large effective range (in addition to a large scattering length), we hope to extend the pertinence of such measurements to neutron matter at densities of astrophysical interest.