Ultrastable super-Tonks-Girardeau gases under weak dipolar interactions

TL;DR

This paper explains the extreme stability of super-Tonks-Girardeau gases with weak dipolar interactions by analyzing spectral responses, showing how tiny dipolar forces selectively affect bound states and extend the gas's stability.

Contribution

It provides an exact solution revealing the spectral mechanism behind the stability of sTG gases under weak dipolar interactions, a novel insight into their robustness.

Findings

Weak dipolar forces cause energy shifts in bound states but not in the sTG branch.

Avoided level crossing is significantly altered by dipolar interactions.

Results are consistent with experimental observations and apply to both bosonic and fermionic systems.

Abstract

The highly excited super-Tonks-Girardeau (sTG) gas was recently observed to be extremely stable in the presence of a weak dipolar repulsion. Here we reveal the underlying reason for this mysterious phenomenon. By exactly solving the trapped small clusters with both contact and dipolar interactions, we show that the reason lies in the distinct spectral responses between sTG gas and its decaying channel (bound state) when turn on a weak dipolar interaction. Specifically, a tiny dipolar force can produce a visible energy shift for the localized bound state, but can hardly affect the extended sTG branch. As a result, the avoided level crossing between two branches is greatly modified in both location and width in the parameter axis of coupling strength, leading to a more (less) stable sTG gas for a repulsive (attractive) dipolar force. These results, consistent with experimental observations, are found to robustly apply to both bosonic and fermionic systems.