66 research outputs found
Angle-resolved photoemission spectroscopy with quantum gas microscopes
Quantum gas microscopes are a promising tool to study interacting quantum
many-body systems and bridge the gap between theoretical models and real
materials. So far they were limited to measurements of instantaneous
correlation functions of the form , even though
extensions to frequency-resolved response functions would provide important information about the elementary
excitations in a many-body system. For example, single particle spectral
functions, which are usually measured using photoemission experiments in
electron systems, contain direct information about fractionalization and the
quasiparticle excitation spectrum. Here, we propose a measurement scheme to
experimentally access the momentum and energy resolved spectral function in a
quantum gas microscope with currently available techniques. As an example for
possible applications, we numerically calculate the spectrum of a single hole
excitation in one-dimensional models with isotropic and anisotropic
antiferromagnetic couplings. A sharp asymmetry in the distribution of spectral
weight appears when a hole is created in an isotropic Heisenberg spin chain.
This effect slowly vanishes for anisotropic spin interactions and disappears
completely in the case of pure Ising interactions. The asymmetry strongly
depends on the total magnetization of the spin chain, which can be tuned in
experiments with quantum gas microscopes. An intuitive picture for the observed
behavior is provided by a slave-fermion mean field theory. The key properties
of the spectra are visible at currently accessible temperatures.Comment: 16+7 pages, 10+2 figure
Ferromagnetism and skyrmions in the Hofstadter–Fermi–Hubbard model
Strongly interacting fermionic systems host a variety of interesting quantum many-body states with exotic excitations. For instance, the interplay of strong interactions and the Pauli exclusion principle can lead to Stoner ferromagnetism, but the fate of this state remains unclear when kinetic terms are added. While in many lattice models the fermions' dispersion results in delocalization and destabilization of the ferromagnet, flat bands can restore strong interaction effects and ferromagnetic correlations. To reveal this interplay, here we propose to study the Hofstadter–Fermi–Hubbard model using ultracold atoms. We demonstrate, by performing large-scale density-matrix renormalization group simulations, that this model exhibits a lattice analog of the quantum Hall (QH) ferromagnet at magnetic filling factor ν = 1. We reveal the nature of the low energy spin-singlet states around ν ≈ 1 and find that they host quasi-particles and quasi-holes exhibiting spin-spin correlations reminiscent of skyrmions. Finally, we predict the breakdown of flat-band ferromagnetism at large fields. Our work paves the way towards experimental studies of lattice QH ferromagnetism, including prospects to study many-body states of interacting skyrmions and explore the relation to high- superconductivity
Time-resolved observation of spin-charge deconfinement in fermionic Hubbard chains
Elementary particles such as the electron carry several quantum numbers, for
example, charge and spin. However, in an ensemble of strongly interacting
particles, the emerging degrees of freedom can fundamentally differ from those
of the individual constituents. Paradigmatic examples of this phenomenon are
one-dimensional systems described by independent quasiparticles carrying either
spin (spinon) or charge (holon). Here we report on the dynamical deconfinement
of spin and charge excitations in real space following the removal of a
particle in Fermi-Hubbard chains of ultracold atoms. Using space- and
time-resolved quantum gas microscopy, we track the evolution of the excitations
through their signatures in spin and charge correlations. By evaluating
multi-point correlators, we quantify the spatial separation of the excitations
in the context of fractionalization into single spinons and holons at finite
temperatures
Evaluation of time-dependent correlators after a local quench in iPEPS: hole motion in the t-J model
Infinite projected entangled pair states (iPEPS) provide a convenient
variational description of infinite, translationally-invariant two-dimensional
quantum states. However, the simulation of local excitations is not directly
possible due to the translationally-invariant ansatz. Furthermore, as iPEPS are
either identical or orthogonal, expectation values between different states as
required during the evaluation of non-equal-time correlators are ill-defined.
Here, we show that by introducing auxiliary states on each site, it becomes
possible to simulate both local excitations and evaluate non-equal-time
correlators in an iPEPS setting under real-time evolution. We showcase the
method by simulating the t-J model after a single hole has been placed in the
half-filled antiferromagnetic background and evaluating both return
probabilities and spin correlation functions, as accessible in quantum gas
microscopes.Comment: 12 pages, 5 figures, minor revision requested by SciPost Physic
Thouless Pumps and Bulk-Boundary Correspondence in Higher-Order Symmetry-Protected Topological Phases
The bulk-boundary correspondence relates quantized edge states to bulk
topological invariants in topological phases of matter. In one-dimensional
symmetry-protected topological systems (SPTs), quantized topological Thouless
pumps directly reveal this principle and provide a sound mathematical
foundation. Symmetry-protected higher-order topological phases of matter
(HOSPTs) also feature a bulk-boundary correspondence, but its connection to
quantized charge transport remains elusive. Here we show that quantized
Thouless pumps connecting -symmetric HOSPTs can be described by a tuple of
four Chern numbers that measure quantized bulk charge transport in a
direction-dependent fashion. Moreover, this tuple of Chern numbers allows to
predict the sign and value of fractional corner charges in the HOSPTs. We show
that the topologically non-trivial phase can be characterized by both
quadrupole and dipole configurations, shedding new light on current debates
about the multi-pole nature of the HOSPT bulk. By employing corner-periodic
boundary conditions, we generalize Restas's theory to HOSPTs. Our approach
provides a simple framework for understanding topological invariants of general
HOSPTs and paves the way for an in-depth description of future dynamical
experiments.Comment: 4 pages, 4 figures plus supplement
Coupling ultracold matter to dynamical gauge fields in optical lattices: From flux attachment to ℤ2 lattice gauge theories
From the standard model of particle physics to strongly correlated electrons, various physical settings are formulated in terms of matter coupled to gauge fields. Quantum simulations based on ultracold atoms in optical lattices provide a promising avenue to study these complex systems and unravel the underlying many-body physics. Here, we demonstrate how quantized dynamical gauge fields can be created in mixtures of ultracold atoms in optical lattices, using a combination of coherent lattice modulation with strong interactions. Specifically, we propose implementation of ℤ2 lattice gauge theories coupled to matter, reminiscent of theories previously introduced in high-temperature superconductivity. We discuss a range of settings from zero-dimensional toy models to ladders featuring transitions in the gauge sector to extended two-dimensional systems. Mastering lattice gauge theories in optical lattices constitutes a new route toward the realization of strongly correlated systems, with properties dictated by an interplay of dynamical matter and gauge fields
Dominant Fifth-Order Correlations in Doped Quantum Antiferromagnets
Traditionally one and two-point correlation functions are used to
characterize many-body systems. In strongly correlated quantum materials, such
as the doped 2D Fermi-Hubbard system, these may no longer be sufficient because
higher-order correlations are crucial to understanding the character of the
many-body system and can be numerically dominant. Experimentally, such
higher-order correlations have recently become accessible in ultracold atom
systems. Here we reveal strong non-Gaussian correlations in doped quantum
anti-ferromagnets and show that higher order correlations dominate over
lower-order terms. We study a single mobile hole in the model using DMRG,
and reveal genuine fifth-order correlations which are directly related to the
mobility of the dopant. We contrast our results to predictions using models
based on doped quantum spin liquids which feature significantly reduced
higher-order correlations. Our predictions can be tested at the lowest
currently accessible temperatures in quantum simulators of the 2D Fermi-Hubbard
model. Finally, we propose to experimentally study the same fifth-order
spin-charge correlations as a function of doping. This will help to reveal the
microscopic nature of charge carriers in the most debated regime of the Hubbard
model, relevant for understanding high- superconductivity.Comment: 4 pages, 4 figures, short supplementar
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