326,990 research outputs found
Spacetime as a quantum many-body system
Quantum gravity has become a fertile interface between gravitational physics
and quantum many-body physics, with its double goal of identifying the
microscopic constituents of the universe and their fundamental dynamics, and of
understanding their collective properties and how spacetime and geometry
themselves emerge from them at macroscopic scales. In this brief contribution,
we outline the problem of quantum gravity from this emergent spacetime
perspective, and discuss some examples in which ideas and methods from quantum
many-body systems have found a central role in quantum gravity research.Comment: 15 pages; invited contribution to "Many-body approaches at different
scales: A tribute to Norman H. March on the occasion of his 90th birthday",
edited by G. G. N. Angilella and C. Amovilli (New York, Springer, 2017 - to
appear
Scrambling and thermalization in a diffusive quantum many-body system
Out-of-time ordered (OTO) correlation functions describe scrambling of
information in correlated quantum matter. They are of particular interest in
incoherent quantum systems lacking well defined quasi-particles. Thus far, it
is largely elusive how OTO correlators spread in incoherent systems with
diffusive transport governed by a few globally conserved quantities. Here, we
study the dynamical response of such a system using high-performance
matrix-product-operator techniques. Specifically, we consider the
non-integrable, one-dimensional Bose-Hubbard model in the incoherent
high-temperature regime. Our system exhibits diffusive dynamics in time-ordered
correlators of globally conserved quantities, whereas OTO correlators display a
ballistic, light-cone spreading of quantum information. The slowest process in
the global thermalization of the system is thus diffusive, yet information
spreading is not inhibited by such slow dynamics. We furthermore develop an
experimentally feasible protocol to overcome some challenges faced by existing
proposals and to probe time-ordered and OTO correlation functions. Our study
opens new avenues for both the theoretical and experimental exploration of
thermalization and information scrambling dynamics.Comment: 7+4 pages, 8+3 figures; streamlined versio
Quantum invariants of motion in a generic many-body system
Dynamical Lie-algebraic method for the construction of local quantum
invariants of motion in non-integrable many-body systems is proposed and
applied to a simple but generic toy model, namely an infinite kicked
chain of spinless fermions. Transition from integrable via {pseudo-integrable
(\em intermediate}) to quantum ergodic (quantum mixing) regime in parameter
space is investigated. Dynamical phase transition between ergodic and
intermediate (neither ergodic nor completely integrable) regime in
thermodynamic limit is proposed. Existence or non-existence of local
conservation laws corresponds to intermediate or ergodic regime, respectively.
The computation of time-correlation functions of typical observables by means
of local conservation laws is found fully consistent with direct calculations
on finite systems.Comment: 4 pages in REVTeX with 5 eps figures include
Coherent Imaging Spectroscopy of a Quantum Many-Body Spin System
Quantum simulators, in which well controlled quantum systems are used to
reproduce the dynamics of less understood ones, have the potential to explore
physics that is inaccessible to modeling with classical computers. However,
checking the results of such simulations will also become classically
intractable as system sizes increase. In this work, we introduce and implement
a coherent imaging spectroscopic technique to validate a quantum simulation,
much as magnetic resonance imaging exposes structure in condensed matter. We
use this method to determine the energy levels and interaction strengths of a
fully-connected quantum many-body system. Additionally, we directly measure the
size of the critical energy gap near a quantum phase transition. We expect this
general technique to become an important verification tool for quantum
simulators once experiments advance beyond proof-of-principle demonstrations
and exceed the resources of conventional computers
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