1,740 research outputs found
Entanglement Cost of Three-Level Antisymmetric States
We show that the entanglement cost of the three-dimensional antisymmetric
states is one ebit.Comment: 8page
Fidelity and Concurrence of conjugated states
We prove some new properties of fidelity (transition probability) and
concurrence, the latter defined by straightforward extension of Wootters
notation. Choose a conjugation and consider the dependence of fidelity or of
concurrence on conjugated pairs of density operators. These functions turn out
to be concave or convex roofs. Optimal decompositions are constructed. Some
applications to two- and tripartite systems illustrate the general theorem.Comment: 10 pages, RevTex, Correction: Enlarged, reorganized version. More
explanation
Electromagnetic wormholes and virtual magnetic monopoles
We describe new configurations of electromagnetic (EM) material parameters,
the electric permittivity and magnetic permeability , that
allow one to construct from metamaterials objects that function as invisible
tunnels. These allow EM wave propagation between two points, but the tunnels
and the regions they enclose are not detectable to EM observations. Such
devices function as wormholes with respect to Maxwell's equations and
effectively change the topology of space vis-a-vis EM wave propagation. We
suggest several applications, including devices behaving as virtual magnetic
monopoles.Comment: 4 pages, 3 figure
Inverse Diffusion Theory of Photoacoustics
This paper analyzes the reconstruction of diffusion and absorption parameters
in an elliptic equation from knowledge of internal data. In the application of
photo-acoustics, the internal data are the amount of thermal energy deposited
by high frequency radiation propagating inside a domain of interest. These data
are obtained by solving an inverse wave equation, which is well-studied in the
literature. We show that knowledge of two internal data based on well-chosen
boundary conditions uniquely determines two constitutive parameters in
diffusion and Schroedinger equations. Stability of the reconstruction is
guaranteed under additional geometric constraints of strict convexity. No
geometric constraints are necessary when internal data for well-chosen
boundary conditions are available, where is spatial dimension. The set of
well-chosen boundary conditions is characterized in terms of appropriate
complex geometrical optics (CGO) solutions.Comment: 24 page
RSFQ Circuitry Using Intrinsic π-Phase Shifts
The latching of temporary data is essential in the rapid single flux quantum (RSFQ) electronics family. Its pulse-driven nature requires two or more stable states in almost all cells. Storage loops must be designed to have exactly two stable states for binary data representation. In conventional RSFQ such loops are constructed to have two stable states, e.g. by using asymmetric bias currents. This bistability naturally occurs when phase-shifting elements are included in the circuitry, such as pi-Josephson junctions or a pi-phase shift associated with an unconventional (d-wave) order parameter symmetry. Both approaches can be treated completely analogously, giving the same results. We have demonstrated for the first time the correct operation of a logic circuit, a toggle-flip-flop, using rings with an intrinsic pi-phase shift (pi-rings) based on hybrid high-Tc to low-Tc Josephson junctions. Because of their natural bistability these pi-rings improve the device symmetry, enhance operation margins and alleviate the need for bias current lines.\ud
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Distinguishability of States and von Neumann Entropy
Consider an ensemble of pure quantum states |\psi_j>, j=1,...,n taken with
prior probabilities p_j respectively. We show that it is possible to increase
all of the pairwise overlaps || i.e. make each constituent pair
of the states more parallel (while keeping the prior probabilities the same),
in such a way that the von Neumann entropy S is increased, and dually, make all
pairs more orthogonal while decreasing S. We show that this phenomenon cannot
occur for ensembles in two dimensions but that it is a feature of almost all
ensembles of three states in three dimensions. It is known that the von Neumann
entropy characterises the classical and quantum information capacities of the
ensemble and we argue that information capacity in turn, is a manifestation of
the distinguishability of the signal states. Hence our result shows that the
notion of distinguishability within an ensemble is a global property that
cannot be reduced to considering distinguishability of each constituent pair of
states.Comment: 18 pages, Latex, 2 figure
A Minkowski Type Trace Inequality and Strong Subadditivity of Quantum Entropy II: Convexity and Concavity
We revisit and prove some convexity inequalities for trace functions
conjectured in the earlier part I. The main functional considered is
\Phi_{p,q}(A_1,A_2,...,A_m) = (trace((\sum_{j=1}^m A_j^p)^{q/p}))^{1/q} for m
positive definite operators A_j. In part I we only considered the case q=1 and
proved the concavity of \Phi_{p,1} for 0 < p \leq 1 and the convexity for p=2.
We conjectured the convexity of \Phi_{p,1} for 1< p < 2. Here we not only
settle the unresolved case of joint convexity for 1 \leq p \leq 2, we are also
able to include the parameter q\geq 1 and still retain the convexity. Among
other things this leads to a definition of an L^q(L^p) norm for operators when
1 \leq p \leq 2 and a Minkowski inequality for operators on a tensor product of
three Hilbert spaces -- which leads to another proof of strong subadditivity of
entropy. We also prove convexity/concavity properties of some other, related
functionals.Comment: Proof of a conjecture in math/0701352. Revised version replaces
earlier draft. 18 pages, late
Temperature effects on mixed state geometric phase
Geometric phase of an open quantum system that is interacting with a thermal
environment (bath) is studied through some simple examples. The system is
considered to be a simple spin-half particle which is weakly coupled to the
bath. It is seen that even in this regime the geometric phase can vary with
temperature. In addition, we also consider the system under an adiabatically
time-varying magnetic field which is weakly coupled to the bath. An important
feature of this model is that it reveals existence of a temperature-scale in
which adiabaticity condition is preserved and beyond which the geometric phase
is varying quite rapidly with temperature. This temperature is exactly the one
in which the geometric phase vanishes. This analysis has some implications in
realistic implementations of geometric quantum computation.Comment: 5 page
Extension of formability of the magnesium wrought alloy AZ31B-O at room temperature by pulse magnetic forming
For having the lowest density of all metal construction materials of 1.75 kg/dm3, magnesium
wrought alloys are outstanding lightweight materials. The low formability at room temperature
limits the industrial use of magnesium AZ31B-O. In this paper the influence of
high strain rates was investigated with the aim to improve the formability of the alloy
AZ31B-O at room temperature.
The negative strain rate sensitivity of quasi-static strain rates causes an early loss of material
stability due to formation of local deformation zones on the work piece surface. This
leads to a low formability in the forming state of plane strain, in which the forming limit
(FLC) of magnesium alloy AZ31B-O has a critical minimum. For process illustration of
multi-axial stress states - which appear in conventional forming processes - the pulse
magnetic forming process is used. To create plane strain formability a flat coil is used. The
applied die is used to control the free formability. Hereby, a change of the maximum loads
on the power transfer zone to areas of plane strain formability occurs.
The results that have been achieved show that high strain rates at room temperature increase
the permitted loads of the material with plane strain formability significantly. High
speed forming is linked to a rising strain rate sensitivity which increases the flow resistance
in critical forming areas, in favor of a rising material stability. This fact is represented
by equally reduction of the sheet thickness on the power transfer area. The homogeneous
work piece stress clearly increases the formability of AZ31B-O at room temperature
compared to quasi-static forming process
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