12 research outputs found
Eigenstate Thermalization in Systems with Spontaneously Broken Symmetry
A strongly non-integrable system is expected to satisfy the eigenstate
thermalization hypothesis, which states that the expectation value of an
observable in an energy eigenstate is the same as the thermal value. This must
be revised if the observable is an order parameter for a spontaneously broken
symmetry, which has multiple thermal values. We propose that in this case the
system is unstable towards forming nearby eigenstates which yield each of the
allowed thermal values. We provide strong evidence for this from a numerical
study of the 2D transverse-field quantum Ising model.Comment: 4 pages, 5 figure
A quantum algorithm for solving open system dynamics on quantum computers using noise
In this paper we present a quantum algorithm that uses noise as a resource.
The goal of our quantum algorithm is the calculation of operator averages of an
open quantum system evolving in time. Selected low-noise system qubits and
noisy bath qubits represent the system and the bath of the open quantum system.
All incoherent qubit noise can be mapped to bath spectral functions. The form
of the spectral functions can be tuned digitally, allowing for the time
evolution of a wide range of open-system models at finite temperature. We study
the feasibility of this approach with a focus on the solution of the spin-boson
model and assume intrinsic qubit noise that is dominated by damping and
dephasing. We find that classes of open quantum systems exist where our
algorithm performs very well, even with gate errors as high as 1%. In general
the presented algorithm performs best if the system-bath interactions can be
decomposed into native gates.Comment: 19 pages, 8 figures in total: 10 pages main text with 7 figure
Imaging signatures of the local density of states in an electronic cavity
We use Scanning Gate Microscopy to study electron transport through an open,
gate-defined resonator in a Ga(Al)As heterostructure. Raster-scanning the
voltage-biased metallic tip above the resonator, we observe distinct
conductance modulations as a function of the tip-position and voltage. Quantum
mechanical simulations reproduce these conductance modulations and reveal their
relation to the partial local density of states in the resonator. Our
measurements illustrate the current frontier between possibilities and
limitations in imaging the local density of states in buried electron systems
using scanning gate microscopy
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Eigenstate thermalization in systems with spontaneously broken symmetry.
A strongly nonintegrable system is expected to satisfy the eigenstate thermalization hypothesis, which states that the expectation value of an observable in an energy eigenstate is the same as the thermal value. This must be revised if the observable is an order parameter for a spontaneously broken symmetry, which has multiple thermal values. We propose that in this case the system is unstable towards forming nearby eigenstates which yield each of the allowed thermal values. We provide strong evidence for this from a numerical study of the two-dimensional transverse-field quantum Ising model
Energy Stability of Branching in the Scanning Gate Response of Two-Dimensional Electron Gases with Smooth Disorder
International audienceThe branched pattern typically observed through the scanning gate microscopy (SGM) of two dimensional electron gases in the presence of weak, smooth disorder has recently been found to be robust against a very large shift in the Fermi energy of the electron gas. We propose a toy model, where the potential landscape reduces to a single localized feature, that makes it possible to recast the understanding of branch formation through the effect of caustics in an appropriate set of classical trajectories, and it is simple enough to allow for a quantitative analysis of the energy and spatial dependence of the branches. We find the energy stability to be extremely generic, as it rests only upon the assumptions of weak disorder, weak scattering, and the proportionality of the SGM response to the density of classical electron trajectories. Therefore, the robustness against changes of the electron’s Fermi energy remains when adopting progressively realistic models of smooth disorder
Signatures of folded branches in the scanning gate microscopy of ballistic electronic cavities
18 pages, 13 figuresInternational audienceWe demonstrate the emergence of classical features in electronic quantum transport for the scanning gate microscopy response in a cavity defined by a quantum point contact and a micron-sized circular reflector. The branches in electronic flow characteristic of a quantum point contact opening on a two-dimensional electron gas with weak disorder are folded by the reflector, yielding a complex spatial pattern. Considering the deflection of classical trajectories by the scanning gate tip allows to establish simple relationships of the scanning pattern, which are in agreement with recent experimental findings