160 research outputs found
Multipartite entanglement generation and fidelity decay in disordered qubit systems
We investigate multipartite entanglement dynamics in disordered spin-1/2
lattice models exhibiting a transition from integrability to quantum chaos.
Borrowing from the recently introduced generalized entanglement framework, we
construct measures for correlations relative to arbitrary local and bi-local
spin observables, and show how they naturally signal the crossover between
distinct dynamical regimes. In particular, we find that the generation of
global entanglement is directly ruled by the local density of states in the
short time limit, whereas the asymptotic amount of entanglement is proportional
to the degree of delocalization of the chaotic many-body state. Our results are
relevant to the stability of quantum information in disordered quantum
computing hardware.Comment: 4 pages, 4 figure
Entanglement production in chaotic quantum dots subject to spin-orbit coupling
We study numerically the production of orbital and spin entangled states in
chaotic quantum dots for non-interacting electrons. The introduction of
spin-orbit coupling permit us to identify signatures of time-reversal symmetry
correlations in the entanglement production previously unnoticed, resembling
weak-(anti)localization quantum corrections to the conductance. We find the
entanglement to be strongly dependent on spin-orbit coupling, showing universal
features for broken time-reversal and spin-rotation symmetries.Comment: 6 pages; extended versio
One-dimensional many-body entangled open quantum systems with tensor network methods
We present a collection of methods to simulate entangled dynamics of open
quantum systems governed by the Lindblad equation with tensor network methods.
Tensor network methods using matrix product states have been proven very useful
to simulate many-body quantum systems and have driven many innovations in
research. Since the matrix product state design is tailored for closed
one-dimensional systems governed by the Schr\"odinger equation, the next step
for many-body quantum dynamics is the simulation of open quantum systems. We
review the three dominant approaches to the simulation of open quantum systems
via the Lindblad master equation: quantum trajectories, matrix product density
operators, and locally purified tensor networks. Selected examples guide
possible applications of the methods and serve moreover as a benchmark between
the techniques. These examples include the finite temperature states of the
transverse quantum Ising model, the dynamics of an exciton traveling under the
influence of spontaneous emission and dephasing, and a double-well potential
simulated with the Bose-Hubbard model including dephasing. We analyze which
approach is favorable leading to the conclusion that a complete set of all
three methods is most beneficial, push- ing the limits of different scenarios.
The convergence studies using analytical results for macroscopic variables and
exact diagonalization methods as comparison, show, for example, that matrix
product density operators are favorable for the exciton problem in our study.
All three methods access the same library, i.e., the software package Open
Source Matrix Product States, allowing us to have a meaningful comparison
between the approaches based on the selected examples. For example, tensor
operations are accessed from the same subroutines and with the same
optimization eliminating one possible bias in a comparison of such numerical
methods.Comment: 24 pages, 8 figures. Small extension of time evolution section and
moving quantum simulators to introduction in comparison to v
Lattice Gauge Tensor Networks
We present a unified framework to describe lattice gauge theories by means of
tensor networks: this framework is efficient as it exploits the high amount of
local symmetry content native of these systems describing only the gauge
invariant subspace. Compared to a standard tensor network description, the
gauge invariant one allows to speed-up real and imaginary time evolution of a
factor that is up to the square of the dimension of the link variable. The
gauge invariant tensor network description is based on the quantum link
formulation, a compact and intuitive formulation for gauge theories on the
lattice, and it is alternative to and can be combined with the global symmetric
tensor network description. We present some paradigmatic examples that show how
this architecture might be used to describe the physics of condensed matter and
high-energy physics systems. Finally, we present a cellular automata analysis
which estimates the gauge invariant Hilbert space dimension as a function of
the number of lattice sites and that might guide the search for effective
simplified models of complex theories.Comment: 28 pages, 9 figure
Method for analyzing web space data
A method for analyzing data from the web that determine the importance that a chosen subject has in society, e.g., subject matter relating a concert, a scientific discovery, a football match, a person, a corporation, a brand, or a car, and analyze such data that can represent the entire society better than the known techniques. The method according to the invention can avoid malicious alterations and is able to measure and detect the temporal relations among all the web resources that talk about a particular topic or subject matter
Dipole oscillations of confined lattice bosons in one dimension
We study the dynamics of a non-integrable system comprising interacting cold
bosons trapped in an optical lattice in one-dimension by means of exact
time-dependent numerical DMRG techniques. Particles are confined by a parabolic
potential, and dipole oscillations are induced by displacing the trap center of
a few lattice sites. Depending on the system parameters this motion can vary
from undamped to overdamped. We study the dipole oscillations as a function of
the lattice displacement, the particle density and the strength of
interparticle interactions. These results explain the recent experiment C.D.
Fertig et al., Phys. Rev. Lett. 94, 120403 (2005).Comment: 4 pages, 3 figure
Multipartite Entanglement Generation and Fidelity Decay in Disordered Qubit Systems
We investigate multipartite entanglement dynamics in disordered spin-1â2 lattice models exhibiting a transition from integrability to quantum chaos. Borrowing from the generalized entanglement framework, we construct measures for correlations relative to arbitrary local and bilocal spin observables, and show how they naturally signal the crossover between distinct dynamical regimes. Analytical estimates are obtained in the short- and long-time limits. Our results are in qualitative agreement with predictions from the random matrix theory and are relevant to both condensed-matter physics and to the stability of quantum information in disordered quantum computing hardware
Ab-initio characterization of the quantum linear-zigzag transition using DMRG
Ions of the same charge inside confining potentials can form crystalline
structures which can be controlled by means of the ions density and of the
external trap parameters. In particular, a linear chain of trapped ions
exhibits a transition to a zigzag equilibrium configuration, which is
controlled by the strength of the transverse confinement. Studying this phase
transition in the quantum regime is a challenging problem, even when employing
numerical methods to simulate microscopically quantum many-body systems. Here
we present a compact analytical treatment to map the original long-range
problem into a short-range quantum field theory on a lattice. We provide a
complete numerical architecture, based on Density Matrix Renormalization Group,
to address the effective quantum phi-four model. This technique is instrumental
in giving a complete characterization of the phase diagram, as well as pinpoint
the universality class of the criticality.Comment: 13 pages, 10 figure
Real-time-dynamics quantum simulation of (1+1)-dimensional lattice QED with Rydberg atoms
We show how to implement a Rydberg-atom quantum simulator to study the nonequilibrium dynamics of an Abelian (1+1)-dimensional lattice gauge theory. The implementation locally codifies the degrees of freedom of a Z3 gauge field, once the matter field is integrated out by means of the Gauss local symmetries. The quantum simulator scheme is based on currently available technology and thus is scalable to considerable lattice sizes. It allows, within experimentally reachable regimes, us to explore different string dynamics and to infer information about the Schwinger U(1) model
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