J. . Halimeh, M. Van Damme, T. Zache, D. Banerjee, P. Hauke Achieving the quantum field theory limit in far-from-equilibrium quantum link models,
arXiv:2112.04501 arXiv:2112.04501 (ID: 720766)
Realizations of gauge theories in setups of quantum synthetic matter open up the possibility of probing salient exotic phenomena in condensed matter and high-energy physics, along with potential applications in quantum information and science technologies. In light of the impressive ongoing efforts to achieve such realizations, a fundamental question regarding quantum link model regularizations of lattice gauge theories is how faithfully they capture the quantum field theory limit of gauge theories. Recent work [Zache, Van Damme, Halimeh, Hauke, and Banerjee, (arXiv:2104.00025)] has shown through analytic derivations, exact diagonalization, and infinite matrix product state calculations that the low-energy physics of U(1) quantum link models approaches the quantum field theory limit already at small link spin length S. Here, we show that the approach to this limit also lends itself to the far-from-equilibrium quench dynamics of lattice gauge theories, as demonstrated by our numerical simulations of the Loschmidt return rate and the chiral condensate in infinite matrix product states, which work directly in the thermodynamic limit. Similar to our findings in equilibrium that show a distinct behavior between half-integer and integer link spin lengths, we find that criticality emerging in the Loschmidt return rate is fundamentally different between half-integer and integer spin quantum link models in the regime of strong electric-field coupling. Our results further affirm that state-of-the-art finite-size ultracold-atom and NISQ-device implementations of quantum link lattice gauge theories have the real potential to simulate their quantum field theory limit even in the far-from-equilibrium regime.
A. M. Green, A. Elben, C. Huerta Alderete, L. K. Joshi, N. H. Nguyen, T. Zache, Y. Zhu, B. Sundar, N. M. Linke Experimental measurement of out-of-time-ordered correlators at finite temperature,
arXiv:2112.02068v1 arXiv:2112.02068v1 (ID: 720746)
Out-of-time-ordered correlators (OTOCs) are a key observable in a wide range of interconnected fields including many-body physics, quantum information science, and quantum gravity. The ability to measure OTOCs using near-term quantum simulators will extend our ability to explore fundamental aspects of these fields and the subtle connections between them. Here, we demonstrate the first experimental measurement of OTOCs at finite temperatures and study their temperature dependence. These measurements are performed on a digital quantum computer running a simulation of the transverse field Ising model. Our flexible method, based on the creation of a thermofield double state, can be extended to other models and enables us to probe the OTOC's temperature-dependent decay rate. Measuring this decay rate opens up the possibility of testing the fundamental temperature-dependent bounds on quantum information scrambling.
N. Mueller, T. Zache, R. Ott Quantum thermalization of gauge theories: chaos, turbulence and universality,
arXiv:2111.01155 arXiv:2111.01155 (ID: 720769)
In this talk, we discuss real-time thermalization dynamics of Z2 Lattice Gauge Theory in 2+1 spacetime dimensions. While classical thermalization is commonly associated with chaotic behavior, turbulence and universality, the manifestation of these phenomena in quantum mechanical systems is not clear. However, when viewed through the lens of Entanglement Structure, we find that quantum thermalization proceeds in characteristic stages and reveals phenomena remarkably similar to their classical counterparts: chaos, turbulence and universality.
T. Zache, C. Kokail, B. Sundar, P. Zoller Entanglement Spectroscopy and probing the Li-Haldane Conjecture in Topological Quantum Matter,
arXiv:2110.03913 arXiv:2110.03913 (ID: 720692)
Topological phases are characterized by their entanglement properties, which is manifest in a direct relation between entanglement spectra and edge states discovered by Li and Haldane. We propose to leverage the power of synthetic quantum systems for measuring entanglement via the Entanglement Hamiltonian to probe this relationship experimentally. This is made possible by exploiting the quasi-local structure of Entanglement Hamiltonians. The feasibility of this proposal is illustrated for two paradigmatic examples realizable with current technology, an integer quantum Hall state of non-interacting fermions on a 2D lattice and a symmetry protected topological state of interacting fermions on a 1D chain. Our results pave the road towards an experimental identification of topological order in strongly correlated quantum many-body systems.
V. Kuzmin, T. Zache, L. Pastori, A. Celi, M. Baranov, P. Zoller Probing infinite many-body quantum systems with finite size quantum simulators,
arXiv:2108.12378 arXiv:2108.12378 (ID: 720681)
Experimental studies of synthetic quantum matter are necessarily restricted to approximate ground states prepared on finite-size quantum simulators, which limits their reliability for strongly correlated systems, for instance in the vicinity of a quantum phase transition (QPT). Here, we propose a protocol that makes optimal use of a given finite system size by directly preparing, via coherent evolution with a local deformation of the system Hamiltonian, a part of the translation-invariant infinite-sized system as a mixed state representing the reduced density operator. For systems of free fermions in one and two spatial dimensions, we illustrate and explain the underlying physics, which consists of quasi-particle transport towards the system's boundaries while retaining the bulk "vacuum". For the example of a non-integrable extended Su-Schrieffer-Heeger model, we demonstrate that our protocol enables a more accurate study of QPTs.
N. Mueller, T. Zache, R. Ott Thermalization of Gauge Theories from their Entanglement Spectrum,
arXiv:2107.11416 arXiv:2107.11416 (ID: 720771)
Using dual theories embedded into a larger unphysical Hilbert space along entanglement cuts, we study the Entanglement Structure of Z2 lattice gauge theory in (2+1) spacetime dimensions. We find that Li and Haldane's conjecture holds for gauge theories, and show consistency of the Entanglement Hamiltonian with the Bisognano-Wichmann theorem. Studying non-equilibrium dynamics after a quench, we provide a complete description of thermalization in Z2 gauge theory which proceeds in a characteristic sequence: Maximization of the Schmidt rank and spreading of level repulsion at early times, self-similar evolution with scaling coefficients α=0.8±0.1 and β=0.05±0.03 at intermediate times, and finally thermal saturation of the von Neumann entropy.
T. Zache, M. Van Damme, J. . Halimeh, P. Hauke, D. Banerjee Achieving the continuum limit of quantum link lattice gauge theories on quantum devices,
arXiv:2104.00025 arXiv:2104.00025 (ID: 720772)
The solution of gauge theories is one of the most promising applications of quantum technologies. Here, we discuss the approach to the continuum limit for U(1) gauge theories regularized via finite-dimensional Hilbert spaces of quantum spin-S operators, known as quantum link models. For quantum electrodynamics (QED) in one spatial dimension, we numerically demonstrate the continuum limit by extrapolating the ground state energy, the scalar, and the vector meson masses to large spin lengths S, large volume N, and vanishing lattice spacing a. By analytically solving Gauss' law for arbitrary S, we obtain a generalized PXP spin model and count the physical Hilbert space dimension analytically. This allows us to quantify the required resources for reliable extrapolations to the continuum limit on quantum devices. We use a functional integral approach to relate the model with large values of half-integer spins to the physics at topological angle Θ=π. Our findings indicate that quantum devices will in the foreseeable future be able to quantitatively probe the QED regime with quantum link models.