Dipolar Gas Chilled to Near Zero

Christopher Ticknor

Mansoor Sheik‐Bahae, Denis V. Seletskiy

Dajun Wang, Kang-Kuen Ni, Silke Ospelkaus +6 more

Ran Qi, Zhe-Yu Shi, Hui Zhai

It is known from the solution of the two-body problem that an anisotropic dipolar interaction can give rise to s-wave scattering resonances, which are named dipolar interaction induced resonances (DIIR). In this Letter, we study the zero-temperature many-body physics of a two-component Fermi gas across a DIIR. In the low-density regime, it is very striking that the resulting pairing order parameter is a nearly isotropic singlet pairing and the physics can be well described by an s-wave resonant interaction potential with finite range conditions, despite the anisotropic nature of the dipolar interaction. The pairing energy is as strong as a unitary Fermi gas near a magnetic Feshbach resonance. In the high-density regime, the anisotropic effect plays an important role. We find phase transitions from singlet pairing to a state with mixed singlet and triplet pairing and then from mixed pairing to pure triplet pairing. The state with mixed pairing spontaneously breaks the time-reversal symmetry.

Marvin D. Girardeau, G. E. Astrakharchik

The ground state of a one-dimensional (1D) quantum gas of dipoles oriented perpendicular to the longitudinal axis, with a strong 1/x(3) repulsive potential, is studied at low 1D densities n. Near contact the dependence of the many-body wave function on the separation x(jℓ) of two particles reduces to a two-body wave function Ψ(rel)(x(jℓ)). Immediately after a sudden rotation of the dipoles so that they are parallel to the longitudinal axis, this wave function will still be that of the repulsive potential, but since the potential is now that of the attractive potential, it will not be stationary. It is shown that as nd(2)→0 the rate of change of this wave function approaches zero. It follows that for small values of nd(2), this state is metastable and is an analog of the super Tonks-Girardeau state of bosons with a strong zero-range attraction. The dipolar system is equivalent to a spinor Fermi gas with spin z components σ(↑)=[perpendicular] (perpendicular to the longitudinal axis) and σ(↓)=[parallel] (parallel to the longitudinal axis). A Fermi-Fermi mapping from spinor to spinless Fermi gas followed by the standard 1960 Fermi-Bose mapping reduces the Fermi system to a Bose gas. Potential experiments realizing the sudden spin rotation with ultracold dipolar gases are discussed, and a few salient properties of these states are accurately evaluated by a Monte Carlo method.