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arXiv:2412.12425 · Communications Physics

Dynamical Aharonov-Bohm cages and tight meson confinement in a $${{\mathbb{Z}}}_{2}$$-loop gauge theory

Enrico C. Domanti, A. Bermúdez, Luigi Amico A

Published Aug 28, 2025• 3 citations
arXivHTMLPDF

Abstract

Abstract Low-dimensional lattice gauge theories based on simplified gauge groups have emerged as relevant models of charge-confinement that can potentially be realized with quantum simulators. The intertwined dynamics of matter and gauge fields can result in quantum phases of the confined matter that have not yet been fully explored, especially in connection to the underlying mechanisms behind confinement. Here we study the finite-density phases of a $${{\mathbb{Z}}}_{2}$$ Z 2 lattice gauge theory of interconnected loops and dynamical $${{\mathbb{Z}}}_{2}$$ Z 2 charges. We show that the gauge-magnetic flux threading each loop is responsible for a phenomenon of dynamical Aharonov-Bohm caging, determining the confinement of particles into tightly-bound charge-neutral pairs, the $${{\mathbb{Z}}}_{2}$$ Z 2 analogue of mesons. The latter are trapped inside the cages, which become mobile by adding quantum fluctuations through an external electric field. These tightly-bound mesons can either propagate, manifesting a Luttinger liquid behaviour, or form an incompressible Mott insulator. In light of recent trapped-ion experiments for a single $${{\mathbb{Z}}}_{2}$$ Z 2 loop, these phases could be explored in future experiments.

DOI
10.1038/s42005-025-02284-x

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Dynamical Aharonov-Bohm cages and tight meson confinement in a Z2{{\mathbb{Z}}}_{2}Z2​-loop gauge theory
Abstract Low-dimensional lattice gauge theories based on simplified gauge groups have emerged as relevant models of charge-confinement that can potentially be realized with quantum simulators. The intertwined dynamics of matter and gauge fields can result in quantum phases of the confined matter that have not yet been fully explored, especially in connection to the underlying mechanisms behind confinement. Here we study the finite-density phases of a Z2{{\mathbb{Z}}}_{2}Z2​ Z 2 lattice gauge theory of interconnected loops and dynamical Z2{{\mathbb{Z}}}_{2}Z2​ Z 2 charges. We show that the gauge-magnetic flux threading each loop is responsible for a phenomenon of dynamical Aharonov-Bohm caging, determining the confinement of particles into tightly-bound charge-neutral pairs, the Z2{{\mathbb{Z}}}_{2}Z2​ Z 2 analogue of mesons. The latter are trapped inside the cages, which become mobile by adding quantum fluctuations through an external electric field. These tightly-bound mesons can either propagate, manifesting a Luttinger liquid behaviour, or form an incompressible Mott insulator. In light of recent trapped-ion experiments for a single Z2{{\mathbb{Z}}}_{2}Z2​ Z 2 loop, these phases could be explored in future experiments.
Confinement is an ubiquitous phenomenon when matter couples to gauge fields, which manifests itself in a linear string potential between two static charges. Although gauge fields can be integrated out in one dimension, they can mediate nonlocal interactions which in turn influence the paradigmatic Luttinger liquid properties. However, when the charges become dynamical and their densities finite, understanding confinement becomes challenging. Here we show that confinement in 1D Z_{2} lattice gauge theories, with dynamical matter fields and arbitrary densities, is related to translational symmetry breaking in a nonlocal basis. The exact transformation to this string-length basis leads us to an exact mapping of Luttinger parameters reminiscent of a Luther-Emery rescaling. We include the effects of local, but beyond contact, interactions between the matter particles, and show that confined mesons can form a Mott-insulating state when the deconfined charges cannot. While the transition to the Mott state cannot be detected in the Green's function of the charges, we show that the metallic state is characterized by hidden off-diagonal quasi-long-range order. Our predictions provide new insights to the physics of confinement of dynamical charges, and can be experimentally addressed in Rydberg-dressed quantum gases in optical lattices.
Abstract Coupling dynamical charges to gauge fields can result in highly non-local interactions with a linear confining potential. As a consequence, individual particles bind into mesons which, in one dimension, become the new constituents of emergent Luttinger liquids (LLs). Furthermore, at commensurate fillings, different Mott-insulating states can be stabilized by including nearest-neighbour (NN) interactions among charges. However, rich phase diagrams expected in such models have not been fully explored and still lack comprehensive theoretical explanation. Here, by combining numerical and analytical tools, we study a simple one-dimensional Z 2 lattice gauge theory at half-filling, where U(1) matter is coupled to gauge fields and interacts through NN repulsion. We uncover a rich phase diagram where the local NN interaction stabilizes a Mott state of individual charges (or partons) on the one hand, and an LL of confined mesons on the other. Furthermore, at the interface between these two phases, we uncover a highly frustrated regime arising due to the competition between the local NN repulsion and the non-local confining interactions, realizing a pre-formed parton plasma. Our work is motivated by the recent progress in ultracold atom experiments, where such simple model could be readily implemented. For this reason we calculate the static structure factor which we propose as a simple probe to explore the phase diagram in an experimental setup.
Gauge theories arise in physical systems displaying space-time local symmetries. They provide a powerful description of important realms of physics ranging from fundamental interactions to statistical mechanics, condensed matter, and, more recently, quantum computation. As such, a remarkably deep understanding has been achieved in the field. With the advent of quantum technology, lower energy analogs, capable of capturing important features of the original quantum field theories through quantum simulation, have been intensively studied. Here, we propose a specific scheme implementing an quantum simulation of lattice gauge theories constrained to mesoscopic spatial scales. To this end, we study the dynamics of mesons residing in a ring-shaped lattice of mesoscopic size pierced by an effective magnetic field. In particular, we find a type of Aharonov-Bohm effect that goes beyond the particlelike effect, reflecting the features of the confining gauge potential. The coherence properties of the meson are quantified by the persistent current and by specific features of the correlation functions. When the magnetic field is quenched, Aharonov-Bohm oscillations and correlations start a specific matter-wave current dynamics. Published by the American Physical Society 2024
Aharonov–Bohm interference in a Z2{\pmb{\mathbb{Z}}}_{\bf{2}}Z2​ lattice gauge theory on a hybrid qubit–oscillator quantum computer
Abstract Lattice gauge theories, which have both dynamical matter and gauge fields, are strongly coupled problems that lie beyond the reach of classical computation. Quantum simulations may provide a tractable approach for studying lattice gauge theories, but implementing gauge-invariant encodings and real-time evolution remains experimentally challenging. Here we demonstrate a resource-efficient encoding of a Z2{{\mathbb{Z}}}_{2}Z2​ Z 2 lattice gauge theory using a hybrid qubit–oscillator trapped-ion quantum device, with the qubits representing the gauge fields and the vibrational modes of the ions encoding the bosonic matter fields. We use synthetic dimensions to construct higher dimensional lattice geometries, and we combine digital and analogue techniques to prepare the initial states, realize the gauge-invariant real-time evolution and measure the relevant observables. After observing dynamics obeying Gauss’s law in a Z2{{\mathbb{Z}}}_{2}Z2​ Z 2 link, we extend this approach to a loop geometry formed by two qubits and two oscillators. In this quasi-two-dimensional set-up, we observe Aharonov–Bohm interference with dynamical gauge fields encoding the magnetic flux, thereby demonstrating the interplay between charge and flux. Our results establish a path for scalable quantum simulations of lattice gauge theories in higher dimensions.
Symmetry-protected topology and deconfined solitons in a multi-link Z2\mathbb{Z}_2Z2​ gauge theory
With the advent of quantum simulators, exploring exotic collective phenomena in lattice models with local symmetries and unconventional geometries is at reach of near-term experiments. Motivated by recent progress in this direction, we study a Z2\mathbb{Z}_2Z2​ lattice gauge theory defined on a multi-graph with links that can be visualized as great circles of a spherical shell hosting the Z2\mathbb{Z}_2Z2​ gauge fields. Elementary Wilson loops along pairs of these bonds allow to identify a dynamical gauge-invariant flux, responsible for Aharonov-Bohm-like interference effects in the tunneling dynamics of charged matter residing on the vertices. Focusing on an odd number of links, we show that this leads to state-dependent tunneling amplitudes underlying a phenomenon analogous to the Peierls instability. We find inhomogeneous phases in which an ordered pattern of the gauge fluxes spontaneously breaks translational invariance, and intertwines with a bond order wave for the gauge-invariant kinetic matter operators. Long-range order is shown to coexist with symmetry protected topological order, which survives the quantum fluctuations of the gauge flux induced by an external electric field. Doping the system above half filling leads to the formation of topological soliton/anti-soliton pairs interpolating between different inhomogeneous orderings of the gauge fluxes. By performining a detailed analysis based on matrix product states, we prove that charge deconfinement emerges as a consequence of charge-fractionalization. Quasiparticles carrying fractional charge and bound at the soliton centers can be arbitrarily separated without feeling a confining force, in spite of the long-range attractive interactions set by the small electric field on the individual integer charges.
Exploring confinement transitions in Z2\mathbb{Z}_2Z2​ lattice gauge theories with dipolar atoms beyond one dimension
Confinement of particles into bound states is a phenomenon spanning from high-energy to condensed matter physics, which can be studied in the framework of lattice gauge theories (LGTs). Achieving a comprehensive understanding of confinement continues to pose a major challenge, in particular at finite matter density and in the presence of strong quantum fluctuations. State-of-the-art quantum simulators constitute a promising platform to address this problem. Here we study confinement in coupled chains of Z2\mathbb{Z}_2Z2​ LGTs coupled to matter fields, that can be mapped to a mixed-dimensional (mixD) XXZ model. We perform large-scale numerical matrix-product state calculations to obtain the phase diagram of this model, in which we uncover striped phases formed by the Z2\mathbb{Z}_2Z2​ charges that can be melted at finite temperature or by increasing the tunneling rate. To explore this setting experimentally, we use our quantum simulator constituted by erbium atoms with dipolar interactions in a quantum gas microscope, and observe the predicted melting of a stripe phase by increasing the particle tunneling rate. Our explorative experimental studies of thermal deconfinement of Z2\mathbb{Z}_2Z2​ charges motivate our further theoretical study of the mixD Z2\mathbb{Z}_2Z2​ LGT, in which we predict a confined meson gas at finite temperature and low magnetization where thermal fluctuations destroy stripes but enable spontaneous commensurate spin order. Overall, we demonstrate that our platform can be used to study confinement in Z2\mathbb{Z}_2Z2​ LGTs coupled to matter fields, including long-range interactions and beyond one dimension, paving the way for future research of confinement in the quantum many-body regime.