Fermionizing a small gas of ultracold bosons

TL;DR

This paper demonstrates that a rapidly-rotating ultracold bosonic gas with internal degrees of freedom maps onto a system of non-interacting fermions, revealing fractional quantum Hall states and anyonic excitations.

Contribution

It introduces a mapping of rotating bosonic gases to fermionic systems, enabling analysis of quantum Hall states and anyons in ultracold atomic gases.

Findings

Bosonic system spectrum matches that of effective fermions.

Fractional quantum Hall states emerge at specific spin degeneracies.

Anyons with fractional statistics can be created using polarized lasers.

Abstract

We study the physics of a rapidly-rotating gas of ultracold atomic bosons, with an internal degree of freedom. We show that in the limit of rapid rotation of the trap the problem exactly maps onto that of non-interacting fermions with spin in the lowest Landau level. The spectrum of the real bosonic system is identical to the one of the effective fermions, with the same eigenvalues and the same density of states. When the ratio of the number of atoms to the spin degeneracy is an integer number, the ground state for the effective fermions is an integer quantum Hall state. The corresponding bosonic state is a fractional quantum Hall liquid whose filling factor ranges in the sequence nu=1/2, 2/3, 3/4, ..., as the spin degeneracy increases. Anyons with 1/2,1/3,1/4, ... statistics can be created by inserting lasers with the appropriate polarizations. A special situation appears when the spin degeneracy equals the number of atoms in the gas. The ground state is then the product of a completely antisymmetric spin state and a nu=1 Laughlin state. In this case the system exhibits fermionic excitations with fermionic statistics though the real components are bosonic atoms.