770 research outputs found
Reliable entanglement transfer between pure quantum states
The problem of the reliable transfer of entanglement from one pure bipartite
quantum state to another using local operations is analyzed. It is shown that
in the case of qubits the amount that can be transferred is restricted to the
difference between the entanglement of the two states. In the presence of a
catalytic state the range of the transferrable amount broadens to a certain
degree.Comment: 6 pages, 4 pictures; revised version; to appear in Phys. Rev.
Optimal amount of entanglement to distinguish quantum states instantaneously
We introduce a new aspect of nonlocality which arises when the task of
quantum states distinguishability is considered under local operations and
shared entanglement in the absence of classical communication. We find the
optimal amount of entanglement required to accomplish the task perfectly for
sets of orthogonal states and argue that it quantifies information nonlocality.This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevA.92.05233
Solitary vortex couples in viscoelastic Couette flow
We report experimental observation of a localized structure, which is of a
new type for dissipative systems. It appears as a solitary vortex couple
("diwhirl") in Couette flow with highly elastic polymer solutions. A unique
property of the diwhirls is that they are stationary, in contrast to the usual
localized wave structures in both Hamiltonian and dissipative systems which are
stabilized by wave dispersion. It is also a new object in fluid dynamics - a
couple of vortices that build a single entity somewhat similar to a magnetic
dipole. The diwhirls arise as a result of a purely elastic instability through
a hysteretic transition at negligible Reynolds numbers. It is suggested that
the vortex flow is driven by the same forces that cause the Weissenberg effect.
The diwhirls have a striking asymmetry between the inflow and outflow, which is
also an essential feature of the suggested elastic instability mechanism.Comment: 9 pages (LaTeX), 5 Postscript figures, submitte
Single polymer dynamics: coil-stretch transition in a random flow
By quantitative studies of statistics of polymer stretching in a random flow
and of a flow field we demonstrate that the stretching of polymer molecules in
a 3D random flow occurs rather sharply via the coil-stretch transition at the
value of the criterion close to theoretically predicted.Comment: 4 pages, 5 figure
"Quantumness" versus "classicality" of quantum states and quantum protocols
Entanglement is one of the pillars of quantum mechanics and quantum information processing, and as a result, the quantumness of nonentangled states has typically been overlooked and unrecognized until the last decade. We give a robust definition for the classicality versus quantumness of a single multipartite quantum state, a set of states, and a protocol using quantum states. We show a variety of nonentangled (separable) states that exhibit interesting quantum properties, and we explore the "zoo" of separable states; several interesting subclasses are defined based on the diagonalizing bases of the states, and their nonclassical behavior is investigated.The work of BG was funded by EPSRC and Sidney Sussex College, Cambridge. T.M was funded by the Wolfson Foundation and the Israeli MOD Research and Technology Unit. AB and TM were partly supported The Gerald Schwartz & Heather Reis- man Foundation
Solitary coherent structures in viscoelastic shear flow: computation and mechanism
Starting from stationary bifurcations in Couette-Dean flow, we compute
nontrivial stationary solutions in inertialess viscoelastic circular Couette
flow. These solutions are strongly localized vortex pairs, exist at arbitrarily
large wavelengths, and show hysteresis in the Weissenberg number, similar to
experimentally observed ``diwhirl'' patterns. Based on the computed velocity
and stress fields, we elucidate a heuristic, fully nonlinear mechanism for
these flows. We propose that these localized, fully nonlinear structures
comprise fundamental building blocks for complex spatiotemporal dynamics in the
flow of elastic liquids.Comment: 5 pages text and 4 figures. Submitted to Physical Review Letter
Backward Evolving Quantum States
The basic concept of the two-state vector formalism, which is the time
symmetric approach to quantum mechanics, is the backward evolving quantum
state. However, due to the time asymmetry of the memory's arrow of time, the
possible ways to manipulate a backward evolving quantum state differ from those
for a standard, forward evolving quantum state. The similarities and the
differences between forward and backward evolving quantum states regarding the
no-cloning theorem, nonlocal measurements, and teleportation are discussed. The
results are relevant not only in the framework of the two-state vector
formalism, but also in the framework of retrodictive quantum theory.Comment: Contribution to the J.Phys. A special issue in honor of GianCarlo
Ghirard
Stretching of polymers in a random three-dimensional flow
Behavior of a dilute polymer solution in a random three-dimensional flow with
an average shear is studied experimentally. Polymer contribution to the shear
stress is found to be more than two orders of magnitude higher than in a
laminar shear flow. The results indicate that the polymer molecules get
strongly stretched by the random motion of the fluid.Comment: 4 pages, 3 figure
Elastic turbulence in curvilinear flows of polymer solutions
Following our first report (A. Groisman and V. Steinberg, \sl Nature , 53 (2000)) we present an extended account of experimental observations of
elasticity induced turbulence in three different systems: a swirling flow
between two plates, a Couette-Taylor (CT) flow between two cylinders, and a
flow in a curvilinear channel (Dean flow). All three set-ups had high ratio of
width of the region available for flow to radius of curvature of the
streamlines. The experiments were carried out with dilute solutions of high
molecular weight polyacrylamide in concentrated sugar syrups. High polymer
relaxation time and solution viscosity ensured prevalence of non-linear elastic
effects over inertial non-linearity, and development of purely elastic
instabilities at low Reynolds number (Re) in all three flows. Above the elastic
instability threshold, flows in all three systems exhibit features of developed
turbulence. Those include: (i)randomly fluctuating fluid motion excited in a
broad range of spatial and temporal scales; (ii) significant increase in the
rates of momentum and mass transfer (compared to those expected for a steady
flow with a smooth velocity profile). Phenomenology, driving mechanisms, and
parameter dependence of the elastic turbulence are compared with those of the
conventional high Re hydrodynamic turbulence in Newtonian fluids.Comment: 23 pages, 26 figure
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