Physics World

Fractional quantum Hall state appears in ultracold atoms

Isabelle Dumé

Published Sep 1, 2023• 0 citations

Abstract

Physicists in the US have created a novel strongly interacting quantum liquid known as a “Laughlin state” in a gas of ultracold atoms for the first time.

DOI: 10.1088/2058-7058/36/09/10

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Physics World

Fractional quantum Hall state appears in ultracold atoms

Isabelle Dumé

Published Sep 1, 2023• 0 citations

Publisher

Abstract

Physicists in the US have created a novel strongly interacting quantum liquid known as a “Laughlin state” in a gas of ultracold atoms for the first time.

DOI: 10.1088/2058-7058/36/09/10

Related papers

Fractional quantum Hall regime of a gas of ultracold atoms

B. Paredes, P. Zoller, J. I. Cirac

Solid State CommunicationsJun 3, 200342 citations

Realization of a fractional quantum Hall state with ultracold atoms

Julian Léonard, Sooshin Kim, Joyce Kwan +5 more

Strongly interacting topological matter exhibits fundamentally new phenomena with potential applications in quantum information technology. Emblematic instances are fractional quantum Hall states, where the interplay of magnetic fields and strong interactions gives rise to fractionally charged quasi-particles, long-ranged entanglement, and anyonic exchange statistics. Progress in engineering synthetic magnetic fields has raised the hope to create these exotic states in controlled quantum systems. However, except for a recent Laughlin state of light, preparing fractional quantum Hall states in engineered systems remains elusive. Here, we realize a fractional quantum Hall (FQH) state with ultracold atoms in an optical lattice. The state is a lattice version of a bosonic $ν=1/2$ Laughlin state with two particles on sixteen sites. This minimal system already captures many hallmark features of Laughlin-type FQH states: we observe a suppression of two-body interactions, we find a distinctive vortex structure in the density correlations, and we measure a fractional Hall conductivity of $σ_\text{H}/σ_0= 0.6(2)$ via the bulk response to a magnetic perturbation. Furthermore, by tuning the magnetic field we map out the transition point between the normal and the FQH regime through a spectroscopic probe of the many-body gap. Our work provides a starting point for exploring highly entangled topological matter with ultracold atoms.Strongly interacting topological matter exhibits fundamentally new phenomena with potential applications in quantum information technology. Emblematic instances are fractional quantum Hall states, where the interplay of magnetic fields and strong interactions gives rise to fractionally charged quasi-particles, long-ranged entanglement, and anyonic exchange statistics. Progress in engineering synthetic magnetic fields has raised the hope to create these exotic states in controlled quantum systems. However, except for a recent Laughlin state of light, preparing fractional quantum Hall states in engineered systems remains elusive. Here, we realize a fractional quantum Hall (FQH) state with ultracold atoms in an optical lattice. The state is a lattice version of a bosonic $ν=1/2$ Laughlin state with two particles on sixteen sites. This minimal system already captures many hallmark features of Laughlin-type FQH states: we observe a suppression of two-body interactions, we find a distinctive vortex structure in the density correlations, and we measure a fractional Hall conductivity of $σ_\text{H}/σ_0= 0.6(2)$ via the bulk response to a magnetic perturbation. Furthermore, by tuning the magnetic field we map out the transition point between the normal and the FQH regime through a spectroscopic probe of the many-body gap. Our work provides a starting point for exploring highly entangled topological matter with ultracold atoms.

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Ultracold Fermions Enter the Fractional Quantum Hall Arena

Fabian Grusdt

By controlling the motion and interaction of individual atoms in a cold-atom ensemble, researchers have produced a correlated topological state of matter, called a fractional quantum Hall state.

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Fermionizing a small gas of ultracold bosons

B. Paredes, P. Zoller, J. I. Cirac

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 noninteracting 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 $\ensuremath{\nu}=1/2,2/3,3/4,\dots{},$ as the spin degeneracy increases. Anyons with $1/2,1/3,1/4,\dots{}$ 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 $\ensuremath{\nu}=1$ Laughlin state. In this case the system exhibits fermionic excitations with fermionic statistics although the real components are bosonic atoms.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 noninteracting 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 $\ensuremath{\nu}=1/2,2/3,3/4,\dots{},$ as the spin degeneracy increases. Anyons with $1/2,1/3,1/4,\dots{}$ 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 $\ensuremath{\nu}=1$ Laughlin state. In this case the system exhibits fermionic excitations with fermionic statistics although the real components are bosonic atoms.

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Adiabatic path to fractional quantum Hall states of a few bosonic atoms

M. Popp, B. Paredes, J. I. Cirac

We propose a realistic scheme to create motionally entangled states of a few bosonic atoms. It can experimentally be realized with a gas of ultracold bosonic atoms trapped in a deep optical lattice potential. By simultaneously deforming and rotating the trapping potential on each lattice site it is feasible to adiabatically create a variety of entangled states on each lattice well. We fully address the case of $N=2$ and 4 atoms per well and identify a sequence of fractional quantum Hall states: the Pfaffian state, the $1∕2$ -Laughlin quasiparticle, and the $1∕2$ -Laughlin state. Exact knowledge of the spectrum has allowed us to design adiabatic paths to these states, with all times and parameters well within the reach of current experimental setups. We further discuss the detection of these states by measuring different properties as their density profile, angular momentum, or correlation functions.We propose a realistic scheme to create motionally entangled states of a few bosonic atoms. It can experimentally be realized with a gas of ultracold bosonic atoms trapped in a deep optical lattice potential. By simultaneously deforming and rotating the trapping potential on each lattice site it is feasible to adiabatically create a variety of entangled states on each lattice well. We fully address the case of $N=2$ and 4 atoms per well and identify a sequence of fractional quantum Hall states: the Pfaffian state, the $1∕2$-Laughlin quasiparticle, and the $1∕2$-Laughlin state. Exact knowledge of the spectrum has allowed us to design adiabatic paths to these states, with all times and parameters well within the reach of current experimental setups. We further discuss the detection of these states by measuring different properties as their density profile, angular momentum, or correlation functions.

arXiv:cond-mat/0405195Physical Review ANov 17, 200476 citations

ν=1/2

Laughlin state with two particles on sixteen sites. This minimal system already captures many hallmark features of Laughlin-type FQH states: we observe a suppression of two-body interactions, we find a distinctive vortex structure in the density correlations, and we measure a fractional Hall conductivity of

σ_\text{H}/σ_0= 0.6(2)

via the bulk response to a magnetic perturbation. Furthermore, by tuning the magnetic field we map out the transition point between the normal and the FQH regime through a spectroscopic probe of the many-body gap. Our work provides a starting point for exploring highly entangled topological matter with ultracold atoms.

1/2,1/3,1/4,\dots{}

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 $\ensuremath{\nu}=1$ Laughlin state. In this case the system exhibits fermionic excitations with fermionic statistics although the real components are bosonic atoms.

N=2

and 4 atoms per well and identify a sequence of fractional quantum Hall states: the Pfaffian state, the

1∕2

-Laughlin quasiparticle, and the

1∕2

-Laughlin state. Exact knowledge of the spectrum has allowed us to design adiabatic paths to these states, with all times and parameters well within the reach of current experimental setups. We further discuss the detection of these states by measuring different properties as their density profile, angular momentum, or correlation functions.