Grand-canonical phase diagram and chiral-current suppression at $π$ flux in a bosonic two-leg ladderGrand-canonical phase diagram and chiral-current suppression at $π$ flux in a bosonic two-leg ladder

Meng Zhang, Qingyun Xu, Zhi Lin

We investigate the ground-state phase diagram of repulsively interacting bosons on a two-leg ladder threaded by a uniform artificial magnetic flux, using the cluster Gutzwiller mean-field method. In the strong-rung-coupling regime, self-consistent calculations are performed on a $2\times4$ cluster. By analyzing the superfluid order parameter, leg-resolved currents, chiral current, the current ratio on adjacent legs, and the density imbalance between the two legs, we distinguish Mott-insulating from superfluid regimes and characterize the observed states as Meissner-like, vortex-like (superfluid or Mott insulating), or biased-ladder. In regions overlapping with previous DMRG studies, our results qualitatively agree with the established phase structure, demonstrating that the cluster Gutzwiller approach balances computational efficiency and physical accuracy. We then construct the first grand-canonical $t$ -- $μ$ phase diagrams for this system, revealing how the magnetic flux modifies the shape, tilt, and extent of the Mott lobes. We further explore previously inaccessible regimes, including higher fillings $ρ\gtrsim1$ and the intermediate interaction window $U/t\in[7.69,9.09]$ . Special attention is paid to $φ=π$ , where the effective triangular-ladder mapping becomes singular. Owing to the equivalence of $φ=π$ and $-π$ modulo $2π$ , a combined symmetry forbids net chiral currents, leading to a nonchiral Mott-insulating state, in contrast to the chiral-superfluid tendency expected away from $φ=π$ . Our results offer a computationally efficient route for mapping the global phase structure of bosonic flux ladders and provide guidance for future ultracold-atom experiments in artificial gauge fields.We investigate the ground-state phase diagram of repulsively interacting bosons on a two-leg ladder threaded by a uniform artificial magnetic flux, using the cluster Gutzwiller mean-field method. In the strong-rung-coupling regime, self-consistent calculations are performed on a $2\times4$ cluster. By analyzing the superfluid order parameter, leg-resolved currents, chiral current, the current ratio on adjacent legs, and the density imbalance between the two legs, we distinguish Mott-insulating from superfluid regimes and characterize the observed states as Meissner-like, vortex-like (superfluid or Mott insulating), or biased-ladder. In regions overlapping with previous DMRG studies, our results qualitatively agree with the established phase structure, demonstrating that the cluster Gutzwiller approach balances computational efficiency and physical accuracy. We then construct the first grand-canonical $t$--$μ$ phase diagrams for this system, revealing how the magnetic flux modifies the shape, tilt, and extent of the Mott lobes. We further explore previously inaccessible regimes, including higher fillings $ρ\gtrsim1$ and the intermediate interaction window $U/t\in[7.69,9.09]$. Special attention is paid to $φ=π$, where the effective triangular-ladder mapping becomes singular. Owing to the equivalence of $φ=π$ and $-π$ modulo $2π$, a combined symmetry forbids net chiral currents, leading to a nonchiral Mott-insulating state, in contrast to the chiral-superfluid tendency expected away from $φ=π$. Our results offer a computationally efficient route for mapping the global phase structure of bosonic flux ladders and provide guidance for future ultracold-atom experiments in artificial gauge fields.

arXiv:2606.12159Jun 10, 20260 citations

Chiral quantum optics with giant atoms

Ariadna Soro Álvarez, Anton Frisk Kockum

Bulletin of the American Physical SocietyMar 17, 20210 citations

Observation of interaction-induced asymmetric chiral currents in a synthetic zigzag ladder

Hongxing Zhao, Huiying Du, Yunfei Wang +8 more

Engineering artificial gauge fields in synthetic lattices offers an efficient avenue for exploring topological states in cold atomic physics and photonics in recent years. Interactions between the system constituents in synthetic dimensions become long ranged, and can induce more striking features. Here, we report the experimental observation of asymmetric chiral currents induced by interactions in a synthetic zigzag ladder with tunable staggered flux, based on the laser-driven coupling of discrete momentum states of ultracold $^{133}\mathrm{Cs}$ atoms. We observe that the staggered flux induces the symmetric chiral dynamics along two legs of the zigzag ladder in a noninteracting regime. However, the flux-dependent chiral currents along the two legs become asymmetric with increasing interactions, and the chiral trajectory is changed dramatically under strong interactions. Our finding opens the way for future exploration of exotic dynamics dictated by an interplay of inhomogeneous gauge fields and interactions in synthetic lattices.Engineering artificial gauge fields in synthetic lattices offers an efficient avenue for exploring topological states in cold atomic physics and photonics in recent years. Interactions between the system constituents in synthetic dimensions become long ranged, and can induce more striking features. Here, we report the experimental observation of asymmetric chiral currents induced by interactions in a synthetic zigzag ladder with tunable staggered flux, based on the laser-driven coupling of discrete momentum states of ultracold $^{133}\mathrm{Cs}$ atoms. We observe that the staggered flux induces the symmetric chiral dynamics along two legs of the zigzag ladder in a noninteracting regime. However, the flux-dependent chiral currents along the two legs become asymmetric with increasing interactions, and the chiral trajectory is changed dramatically under strong interactions. Our finding opens the way for future exploration of exotic dynamics dictated by an interplay of inhomogeneous gauge fields and interactions in synthetic lattices.

Physical Review AJul 18, 20252 citations

Chiral Mott insulators, Meissner effect, and Laughlin states in quantum ladders

Alexandru Petrescu, Karyn Le Hur

We introduce generic bosonic models exemplifying that chiral Meissner currents can persist in insulating phases of matter. We first consider interacting bosons on a two-leg ladder. The total density sector can be gapped in a bosonic Mott insulator at odd-integer filling, while the relative density sector remains superfluid due to interchain hopping. Coupling the relative density to gauge fields yields a pseudospin Meissner effect. We show that the same phase arises if the bosons are replaced by spinful fermions confined in Cooper pairs, and find a dual fermionic Mott insulator with spinon currents. We prove that, by tuning the mean density, the Mott insulator with Meissner currents turns into a low-dimensional bosonic $\ensuremath{\nu}=\frac{1}{2}$ Laughlin state for strong enough repulsive interactions across the ladder rungs. We finally discuss extensions to multileg ladders and bilayers in which spinon superfluids with Meissner currents become possible. We propose two experimental realizations, one with ultracold atoms in the setup of Atala et al. [Nat. Phys. 10, 588 (2014)] and another with Josephson junction arrays. We also address a Bose-Fermi mixture subject to a magnetic field in connection with the pseudogap phase of high- ${T}_{c}$ cuprates.We introduce generic bosonic models exemplifying that chiral Meissner currents can persist in insulating phases of matter. We first consider interacting bosons on a two-leg ladder. The total density sector can be gapped in a bosonic Mott insulator at odd-integer filling, while the relative density sector remains superfluid due to interchain hopping. Coupling the relative density to gauge fields yields a pseudospin Meissner effect. We show that the same phase arises if the bosons are replaced by spinful fermions confined in Cooper pairs, and find a dual fermionic Mott insulator with spinon currents. We prove that, by tuning the mean density, the Mott insulator with Meissner currents turns into a low-dimensional bosonic $\ensuremath{\nu}=\frac{1}{2}$ Laughlin state for strong enough repulsive interactions across the ladder rungs. We finally discuss extensions to multileg ladders and bilayers in which spinon superfluids with Meissner currents become possible. We propose two experimental realizations, one with ultracold atoms in the setup of Atala et al. [Nat. Phys. 10, 588 (2014)] and another with Josephson junction arrays. We also address a Bose-Fermi mixture subject to a magnetic field in connection with the pseudogap phase of high-${T}_{c}$ cuprates.

arXiv:1410.6105Physical Review BFeb 26, 201583 citations

Dynamical Tunneling of Ultracold Atoms

W. K. Hensinger, Hartmut Häffner, Antoine Browaeys +7 more

NatureJan 1, 200112 citations

Grand-canonical phase diagram and chiral-current suppression at

π

flux in a bosonic two-leg ladder

2\times4

cluster. By analyzing the superfluid order parameter, leg-resolved currents, chiral current, the current ratio on adjacent legs, and the density imbalance between the two legs, we distinguish Mott-insulating from superfluid regimes and characterize the observed states as Meissner-like, vortex-like (superfluid or Mott insulating), or biased-ladder. In regions overlapping with previous DMRG studies, our results qualitatively agree with the established phase structure, demonstrating that the cluster Gutzwiller approach balances computational efficiency and physical accuracy. We then construct the first grand-canonical

t

μ

phase diagrams for this system, revealing how the magnetic flux modifies the shape, tilt, and extent of the Mott lobes. We further explore previously inaccessible regimes, including higher fillings

ρ\gtrsim1

and the intermediate interaction window

U/t\in[7.69,9.09]

. Special attention is paid to

φ=π

, where the effective triangular-ladder mapping becomes singular. Owing to the equivalence of

φ=π

and

-π

modulo

2π

, a combined symmetry forbids net chiral currents, leading to a nonchiral Mott-insulating state, in contrast to the chiral-superfluid tendency expected away from

φ=π

. Our results offer a computationally efficient route for mapping the global phase structure of bosonic flux ladders and provide guidance for future ultracold-atom experiments in artificial gauge fields.

^{133}\mathrm{Cs}

atoms. We observe that the staggered flux induces the symmetric chiral dynamics along two legs of the zigzag ladder in a noninteracting regime. However, the flux-dependent chiral currents along the two legs become asymmetric with increasing interactions, and the chiral trajectory is changed dramatically under strong interactions. Our finding opens the way for future exploration of exotic dynamics dictated by an interplay of inhomogeneous gauge fields and interactions in synthetic lattices.

{T}_{c}

cuprates.