# Synopsis: One relation to rule them all

Data continue to accumulate showing that an important set of universal relations accurately describes the properties of ultracold fermionic gases.

Quantum gases of ultracold fermions offer a versatile way to study phenomena from quark matter to superconductors. In 2008, Shina Tan (then at the University of Washington) published a set of exact universal relations connecting microscopic quantities with thermodynamic variables under a wide range of conditions. Recently, a group at JILA experimentally verified some of the Tan relations in ultracold potassium-$40$ [1]. Writing in Physical Review Letters, Eva Kuhnle and colleagues at Swinburne University of Technology in Melbourne, Australia, now add to the picture with their results on lithium-$6$.

Kuhnle et al. used Bragg scattering of atoms from a periodic optical potential to verify one of the Tan relations for pair correlations as a function of both the scattering length and probe momentum. This complements the JILA work, which verified a relation between total energy and adiabatic changes in scattering length, and another relation that extends the virial theorem (which expresses total energy in terms of kinetic energy, external potential energy, and interaction energy) to quantum gases. – David Voss

[1] J. T. Stewart, J. P. Gaebler, T. E. Drake, and D. S. Jin, Phys. Rev. Lett. 104, 235301 (2010); see also Viewpoint commentary by D. Sheehy, Physics 3, 48 (2010).

### Announcements

More Announcements »

## Subject Areas

Atomic and Molecular Physics

Optics

Nuclear Physics

## Related Articles

Atomic and Molecular Physics

### Synopsis: Losing Light in a BEC

The index of refraction in a gas of bosons is enhanced relative to its value in a classical gas, a predicted quantum effect that has now been observed in ultracold sodium atoms. Read More »

Atomic and Molecular Physics

### Focus: Atoms As Thermometers

A small number of atoms in repeated trials can accurately measure the temperature of an ultracold gas cloud—a step toward measuring temperature on the micrometer scale. Read More »

Optics

### Synopsis: Bad Cavities for Precise Lasers

The frequency of a laser based on trapped ultracold atoms can be made insensitive to fluctuations in the laser cavity’s length. Read More »