6,795 research outputs found
An observable measure of entanglement for pure states of multi-qubit systems
Recently, Meyer and Wallach [D.A. Meyer and N.R. Wallach (2002), J. of Math.
Phys., 43, pp. 4273] proposed a measure of multi-qubit entanglement that is a
function on pure states. We find that this function can be interpreted as a
physical quantity related to the average purity of the constituent qubits and
show how it can be observed in an efficient manner without the need for full
quantum state tomography. A possible realization is described for measuring the
entanglement of a chain of atomic qubits trapped in a 3D optical lattice.Comment: 8 pages, 2 figure
Why should anyone care about computing with anyons?
In this article we present a pedagogical introduction of the main ideas and
recent advances in the area of topological quantum computation. We give an
overview of the concept of anyons and their exotic statistics, present various
models that exhibit topological behavior, and we establish their relation to
quantum computation. Possible directions for the physical realization of
topological systems and the detection of anyonic behavior are elaborated.Comment: 22 pages, 13 figures. Some changes to existing sections, several
references added, and a new section on criteria for TQO and TQC in lattice
system
Stability of global entanglement in thermal states of spin chains
We investigate the entanglement properties of a one dimensional chain of spin
qubits coupled via nearest neighbor interactions. The entanglement measure used
is the n-concurrence, which is distinct from other measures on spin chains such
as bipartite entanglement in that it can quantify "global" entanglement across
the spin chain. Specifically, it computes the overlap of a quantum state with
its time-reversed state. As such this measure is well suited to study ground
states of spin chain Hamiltonians that are intrinsically time reversal
symmetric. We study the robustness of n-concurrence of ground states when the
interaction is subject to a time reversal antisymmetric magnetic field
perturbation. The n-concurrence in the ground state of the isotropic XX model
is computed and it is shown that there is a critical magnetic field strength at
which the entanglement experiences a jump discontinuity from the maximum value
to zero. The n-concurrence for thermal mixed states is derived and a threshold
temperature is computed below which the system has non zero entanglement.Comment: 13 pages, 3 figures. v.2 includes minor corrections and an added
section treating the quantum XX model with open boundarie
Evaporation of a thin droplet on a thin substrate with a high thermal resistance
A mathematical model for the quasi-steady evaporation of a thin liquid droplet on a thin substrate that incorporates the dependence of the saturation concentration of vapour at the free surface of the droplet on temperature is used to examine an atypical situation in which the substrate has a high thermal resistance relative to the droplet (i.e. it is highly insulating and/or is thick relative to the droplet). In this situation diffusion of heat through the substrate is the rate-limiting evaporative process and at leading order the local mass flux is spatially uniform, the total evaporation rate is proportional to the surface area of the droplet, and the droplet is uniformly cooled. In particular, the qualitative differences between the predictions of the present model in this situation and those of the widely used 'basic' model in which the saturation concentration is independent of temperature are highlighted
Cyclic loading of tendon fascicles using a novel fatigue loading system increases interleukin-6 expression by tenocytes
Repetitive strain or ‘overuse’ is thought to be a major factor contributing to the development of tendinopathy. The aims of our study were to develop a novel cyclic loading system, and use it to investigate the effect of defined loading conditions on the mechanical properties and gene expression of isolated tendon fascicles. Tendon fascicles were dissected from bovine-foot extensors and subjected to cyclic tensile strain (1 Hz) at 30% or 60% of the strain at failure, for 0 h (control), 15 min, 30 min, 1 h, or 5 h. Post loading, a quasi-static test to failure assessed damage. Gene expression at a selected loading regime (1 h at 30% failure strain) was analyzed 6 h post loading by quantitative real-time polymerase chain reaction. Compared with unloaded controls, loading at 30% failure strain took 5 h to lead to a significant decrease in failure stress, whereas loading to 60% led to a significant reduction after 15 min. Loading for 1 h at 30% failure strain did not create significant structural damage, but increased Collagen-1-alpha-chain-1 and interleukin-6 (IL6) expression, suggesting a role of IL6 in tendon adaptation to exercise. Correlating failure properties with fatigue damage provides a method by which changes in gene expression can be associated with different degrees of fatigue damage
Braiding Interactions in Anyonic Quantum Walks
The anyonic quantum walk is a dynamical model describing a single anyon
propagating along a chain of stationary anyons and interacting via mutual
braiding statistics. We review the recent results on the effects of braiding
statistics in anyonic quantum walks in quasi-one dimensional ladder geometries.
For anyons which correspond to spin-1/2 irreps of the quantum groups ,
the non-Abelian species gives rise to entanglement between the
walker and topological degrees of freedom which is quantified by quantum link
invariants over the trajectories of the walk. The decoherence is strong enough
to reduce the walk on the infinite ladder to classical like behaviour. We also
present numerical results on mixing times of or Ising model anyon
walks on cyclic graphs. Finally, the possible experimental simulation of the
anyonic quantum walk in Fractional Quantum Hall systems is discussed.Comment: 13 pages, submitted to Proceedings of the 2nd International
Conference on Theoretical Physics (ICTP 2012
A Quantum Computer Architecture using Nonlocal Interactions
Several authors have described the basic requirements essential to build a
scalable quantum computer. Because many physical implementation schemes for
quantum computing rely on nearest neighbor interactions, there is a hidden
quantum communication overhead to connect distant nodes of the computer. In
this paper we propose a physical solution to this problem which, together with
the key building blocks, provides a pathway to a scalable quantum architecture
using nonlocal interactions. Our solution involves the concept of a quantum bus
that acts as a refreshable entanglement resource to connect distant memory
nodes providing an architectural concept for quantum computers analogous to the
von Neumann architecture for classical computers.Comment: 4 pages, 2 figures, Slight modifications to satisfy referee, 2 new
references, modified acknowledgement. This draft to appear in PRA Rapid
Communication
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