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Patrik Öhberg

Publications and source records attributed to Patrik Öhberg.

At least 19 recordsLinked to original sources
arXiv2025

Quantum Time Crystals and Interacting Chiral Gauge Theories in Atomic BECs III: Role of the Page-Wootters mechanism

We build the case that our published chiral soliton model [Phys. Rev. Lett. 124, 250402 (2019)] can lead to a genuine quantum time crystal for smaller atom numbers. To do this we compare results from the chiral soliton model with exact numerical solutions for the ground state of the three-particle Schrödinger equation in the limit that the spatial profile of the soliton is largely independent of its center-of-mass motion. The connection between the two approaches is found via the Page-Wootters mechanism, and this is what allows for dynamical evolution even in the quantum ground state, as required for a genuine quantum time crystal.

cond-mat.quant-gas↗
arXiv2025

Quantum droplets in a beyond-mean-field density-dependent gauge theory

The beyond-mean-field corrections appropriate to a bosonic many-body system experiencing a density-dependent gauge potential are derived, and from this the dimensional hierarchy of quantum droplet solutions are explored. Non-stationary quantum droplet solutions are supported by a single interaction parameter characterising the strength of the gauge potential, while in one dimension the beyond-mean-field theory can be solved exactly to yield chiral quantum droplets and dark soliton-like excitations. Numerical simulations of single and pairs of chiral droplets indicate a rich dynamics in the beyond-mean-field regime.

cond-mat.quant-gas↗
arXiv2024

A Lower-Dimensional Remnant of Flux Attachment

Flux attachment is a mechanism allowing electric charges to capture magnetic flux in two spatial dimensions. Fundamentally, this is a consequence of the Aharonov-Bohm effect or, in field-theoretic language, of a Chern-Simons term. This is also intimately related to a transmutation of the exchange statistics of the original charges. We show that a remnant of this mechanism is found after a dimensional reduction of a pure Chern-Simons theory and its subsequent coupling to matter.

cond-mat.mes-hall↗
arXiv2024

The Composite Particle Duality: A New Class of Topological Quantum Matter

The composite particle duality extends the notions of both flux attachment and statistical transmutation in spacetime dimensions beyond 2+1D. It constitutes an exact correspondence that can be understood either as a theoretical framework or as a dynamical physical mechanism. The immediate implication of the duality is that an interacting quantum system in arbitrary dimensions can experience a modification of its statistical properties if coupled to a certain gauge field. In other words, commutation relations of quantum fields can be effectively modified by a dynamical physical process. For instance, an originally bosonic quantum fluid in $d$ spatial dimensions can feature composite fermionic (or anyonic) excitations when coupled to a statistical gauge field. In 3+1D the mechanism of flux attachment induces a dynamical formation of dyons as higher-dimensional analogues of Laughlin quasiparticles. In 1+1D there is lack of flux attachment but a remnant in the form of a statistical gauge field can be explicitly constructed. We also introduce a family of interacting quantum many-body systems that undergo statistical transmutation as indicated by the duality. This opens the door to a new realm of topological phases across dimensions both in lattice and continuum systems.

cond-mat.str-el↗
arXiv2024

Dual approach to soft-core anyonic Lieb-Liniger fluids

The identity of quantum matter can be effectively altered by means of gauge fields. In two spatial dimensions this is illustrated by the Chern-Simons flux-attachment mechanism, but such a mechanism is not possible in lower dimensions. Here, we study a one-dimensional interacting Bose gas in the presence of a gauge field. This model can be explicitly mapped into an interacting anyonic system by a large gauge transformation, indicating a statistical transmutation analogous to that of Chern-Simons. The Bogoliubov spectrum in the weakly-interacting limit reveals the presence of a roton minimum arising from the statistical interaction. At a mean-field level chiral solitons are recovered. Should these be understood as quantum bound states, it is natural to interpret them as corresponding to localised anyonic quasiparticles. Hydrodynamic arguments highlight the presence of dispersive chiral shock waves in the propagation of a wavepacket due to a Riemann-Hopf nonlinearity. Numerical calculations show the presence of both chiral soliton trains and shock waves.

cond-mat.quant-gas↗
arXiv2024

Simulation of time crystal behavior for a few boson chiral soliton model in a ring

We present numerical simulations for a chiral soliton model with N=2,3 bosons in a ring, this being a few-particle version of our previous mean-field model for a quantum time crystal. Following Syrwid, Kosior, and Sacha (SKS), the notion is that a precise position measurement of one particle can lead to spontaneous formation of a bright soliton that in a time crystal should rotate intact for at least a few revolutions around the ring. In their work SKS find spontaneous formation of a soliton due to the position measurement, but quantum fluctuations cause the soliton to subsequently decay before it has a chance to perform even one revolution of the ring. Based on this they conclude that time crystal dynamics are impossible. In contrast, for our few boson chiral soliton model, and allowing for imprecise (weak) measurements of the particle position, we show that time crystal behavior is possible allowing for several revolutions of the spontaneously formed soliton around the ring. We therefore argue that our chiral soliton model can realize a quantum time crystal when weak position measurements are allowed for.

cond-mat.quant-gas↗
arXiv2023

The Haldane Model with Chiral Edge States using a Synthetic Dimension

We explicitly show that the differences, with respect to the appearance of topological phases, between the traditional Haldane model, which utilises a honeycomb lattice structure, to that of the Haldane model imbued onto a brick-wall lattice geometry, are inconsequential. A proposal is then put forward to realise the Haldane model by exploiting the internal degrees of freedom of atoms as a synthetic dimension. This leads to a convenient platform for the investigation of chiral edge states due to the hard boundaries provided by the hyperfine manifold. We make some cursory comments on the effects of interactions in the system.

cond-mat.quant-gas↗
arXiv2023

Topological Gauge Fields and the Composite Particle Duality

We introduce topological gauge fields as nontrivial field configurations enforced by topological currents. These fields crucially determine the form of statistical gauge fields that couple to matter and transmute their statistics. We discuss the physical mechanism underlying the composite particle picture and argue that it is a duality of gauge forms that naturally relates to the notion of bosonisation in arbitrary dimensions. This is based on obtaining a generalised version of flux attachment, which yields a density-dependent gauge potential. We recover well-known results, resolve old controversies, and suggest a microscopic mechanism for the emergence of such a gauge field. We also outline potential directions for experimental realisations in ultracold atom platforms.

cond-mat.quant-gas↗
arXiv2022

Interacting Bosons on Crystalline and Quasiperiodic Ladders in a Magnetic Field

We study a variety of Hofstadter ladders in order to probe the interplay between interactions, an applied magnetic field and crystalline or quasiperiodic geometries. Rotational motion will be induced on charged particles when a magnetic field is present, which can result in exotic distributions of current on a lattice. Typically, the geometry of a ladder lattice is assumed to be homogeneous. In this work, however, we will also study ladders that possess non-uniform bond lengths, in order to study the formation of localised currents. By using Density Matrix Renormalisation Group (DMRG) to characterise the quantum phases, we confirm the presence of the usual vortex and Meissner distributions of current, in which particles circulate within the bulk and around the edge respectively. Furthermore, it is also possible to observe variations to these patterns; which combine both vortex and Meissner order, and the onset of incompressible domains for certain fillings of the lattice. If the bond lengths of a ladder fluctuate, we find substantial differences to the structure of currents. This is a consequence of an inhomogeneous, effective magnetic flux, resulting in preferential localisation of currents throughout the lattice bulk, towards the smaller bond lengths. We then find that incompressible domains can significantly grow in size extent across the parameter space, with currents no longer possessing an extended structure across the longitudinal direction of the ladder.

cond-mat.str-el↗
arXiv2022

The gauge coupled two-body problem in a ring

We study the properties of two quantum particles which are confined in a ring. The particles interact via a long-range gauge potential proportional to the distance between the particles. It is found that the two-body ground state corresponds to a state with non-zero angular momentum provided that the interaction between the particles is strong enough. In addition, the particles are correlated in the sense that depending on the interaction strength there is a propensity to be found close together or separated in the ring. We discuss the effect of measuring the position of one of the particles and thereby removing the particle from the ring, where we show that the remaining particle can be prepared in a non-dispersive state with non-zero angular momentum.

quant-ph↗
arXiv2022

Barriers to Macroscopic Superfluidity and Insulation in a 2D Aubry-André Model

We study the ground state phases of interacting bosons in the presence of a 2D Aubry-André potential. By using a a mean-field percolation analysis, we focus on several superlattice and quasicrystalline regimes of the 2D Aubry-André model, including generalisations that account for a tilting or skewing of the potential. We show that barriers to the onset of macroscopic phases naturally arise from weakly modulated domains in the 2D Aubry-André model. This leads to the formation of mixed phases, in which the macroscopic properties are dominated by a minority of the system. The phase diagrams then exhibit substantially different features when compared against crystalline systems, including a lobe-like or wave-like appearance of the Bose glass, sharp extrusions and extended domains with weak percolation. By studying the 2D Aubry-André model across multiple regimes, we have shown that the unique properties of mixed phases are not distinct to a small set of parameters.

cond-mat.str-el↗
arXiv2021

Bulk Localised Transport States in Infinite and Finite Quasicrystals via Magnetic Aperiodicity

Robust edge transport can occur when particles in crystalline lattices interact with an external magnetic field. This system is well described by Bloch's theorem, with the spectrum being composed of bands of bulk states and in-gap edge states. When the confining lattice geometry is altered to be quasicrystaline, then Bloch's theorem breaks down. However, we still expect to observe the basic characteristics of bulk states and current carrying edge states. Here, we show that for quasicrystals in magnetic fields, there is also a third option; the bulk localised transport states. These states share the in-gap nature of the well-known edge states and can support transport along them, but they are fully contained within the bulk of the system, with no support along the edge. We consider both finite and infinite systems, using rigorous error controlled computational techniques that are not prone to finite-size effects. The bulk localised transport states are preserved for infinite systems, in stark contrast to the normal edge states. This allows for transport to be observed in infinite systems, without any perturbations, defects, or boundaries being introduced. We confirm the in-gap topological nature of the bulk localised transport states for finite and infinite systems by computing common topological measures; namely the Bott index and local Chern marker. The bulk localised transport states form due to a magnetic aperiodicity arising from the interplay of length scales between the magnetic field and quasiperiodic lattice. Bulk localised transport could have interesting applications similar to those of the edge states on the boundary, but that could now take advantage of the larger bulk of the lattice. The infinite size techniques introduced here, especially the calculation of topological measures, could also be widely applied to other crystalline, quasicrystalline, and disordered models.

cond-mat.str-el↗
arXiv2021

The Mean-Field Bose Glass in Quasicrystalline Systems

We confirm the presence of a mean-field Bose glass in 2D quasicrystalline Bose-Hubbard models. We focus on two models where the aperiodic component is present in different parts of the problem. First, we consider a 2D generalisation of the Aubry-André model, where the lattice geometry is that of a square with a quasiperiodic onsite potential. Second, we consider the randomly disordered vertex model, which takes aperiodic tilings with non-crystalline rotational symmetries, and forms lattices from the vertices and lengths of the tiles. For the disordered vertex models, the mean-field Bose glass forms across large ranges of the chemical potential, and we observe no significant differences from the case of a square lattice with uniform random disorder. Small variations in the critical points in the presence of random disorder between quasicrystalline and crystalline lattice geometries can be accounted for by the varying coordination number and the different rotational symmetries present. In the 2D Aubry-André model, substantial differences are observed from the usual phase diagrams of crystalline disordered systems. We show that weak modulation lines can be predicted from the underlying potential and may stabilise or suppress the mean-field Bose glass in certain regimes. This results in a lobe-like structure for the mean-field Bose glass in the 2D Aubry-André model, which is significantly different from the case of random disorder. Together, the two quasicrystalline models studied in this work show that the mean-field Bose glass phase is present, as expected for 2D quasiperiodic models. However, a quasicrystalline geometry is not sufficient to result in differences from crystalline realisations of the Bose glass, whereas a quasiperiodic form of disorder can result in different physics, as we observe in the 2D Aubry-André model.

cond-mat.str-el↗
arXiv2020

Gauge transformations and Galilean covariance in nonlinear gauge-coupled quantum fluids

We investigate certain invariance properties of quantum fluids subject to a nonlinear gauge potential. In particular, we derive the covariant transformation laws for the nonlinear potentials under a space-time Galilean boost and consider U(1) gauge transformations. We find that the hydrodynamic canonical field equations are form-invariant in the case of external gauge functions, but not for nonlinear gauge functionals. Hence, nonlinear gauge potentials are non-trivial potentials which may not be "gauged-away". Notably, for a 1D superfluid, attempting to do so generates the gauge-pressure of the fluid in the Hamiltonian density. Further, we investigate how the field equations transform under arbitrary Galilean transformations. We find that the immediate lack of Galilean covariance is restored under a suitably chosen transformation rule set for the potentials, which is identical in form to that of a Schrödinger particle coupled to external scalar and vector potentials.

cond-mat.quant-gas↗
arXiv2020

Synthetic Flux Attachment

Topological field theories emerge at low energy in strongly-correlated condensed matter systems and appear in the context of planar gravity. In particular, the study of Chern-Simons terms gives rise to the concept of flux attachment when the gauge field is coupled to matter, yielding flux-charge composites. Here we investigate the generation of flux attachment in a Bose-Einstein condensate in the presence of non-linear synthetic gauge potentials. In doing so, we identify the U(1) Chern-Simons gauge field as a singular density-dependent gauge potential, which in turn can be expressed as a Berry connection. We envisage a proof-of-concept scheme where the artificial gauge field is perturbatively induced by an effective light-matter detuning created by interparticle interactions. At a mean field level, we recover the action of a "charged" superfluid minimally coupled to both a background and a Chern-Simons gauge field. Remarkably, a localised density perturbation in combination with a non-linear gauge potential gives rise to an effective composite boson model of fractional quantum Hall effect, displaying anyonic vortices.

cond-mat.quant-gas↗
arXiv2020

On the hydrodynamic canonical formalism of the Gross-Pitaevskii field

We derive a canonical formalism for the hydrodynamic representation of the Gross-Pitaevskii field (nonlinear Schrödinger field), where the density and the phase of the condensate form a canonical pair of conjugate field variables. To do so, we treat the meanfield as a singular Lagrangian system and apply both the Dirac-Bergmann and Faddeev-Jackiw methods. The Faddeev-Jackiw method is found to be a more direct approach to the problem.

cond-mat.quant-gas↗
arXiv2020

Response to comment on "Quantum time crystals and interacting gauge theories in atomic Bose-Einstein condensates" by Syrwid, Kosior, and Sacha

In a recent comment [1] on our paper [2] Syrwid, Kosior, and Sacha (SKS) asserted that we did not correctly calculate the chiral soliton energy ${\cal E}_{LAB}$ in the lab frame, and further that the system we proposed is not capable of supporting a genuine quantum time crystal. We concede that we did not correctly calculate ${\cal E}_{LAB}$ but we illustrate below that our system can nonetheless display time crystal behavior with a ground state that is spatially localized and rotating.

cond-mat.quant-gas↗