452 research outputs found
Transfer of d-Level quantum states through spin chains by random swapping
We generalize an already proposed protocol for quantum state transfer to spin
chains of arbitrary spin. An arbitrary unknown level state is transferred
through a chain with rather good fidelity by the natural dynamics of the chain.
We compare the performance of this protocol for various values of . A
by-product of our study is a much simpler method for picking up the state at
the destination as compared with the one proposed previously. We also discuss
entanglement distribution through such chains and show that the quality of
entanglement transition increases with the number of levels .Comment: More discussion about the ground state has been added. Accepted in
Physical Review
On multipartite invariant states II. Orthogonal symmetry
We construct a new class of multipartite states possessing orthogonal
symmetry. This new class defines a convex hull of multipartite states which are
invariant under the action of local unitary operations introduced in our
previous paper "On multipartite invariant states I. Unitary symmetry". We study
basic properties of multipartite symmetric states: separability criteria and
multi-PPT conditions.Comment: 6 pages; slight corrections + new reference
Properties of Entanglement Monotones for Three-Qubit Pure States
Various parameterizations for the orbits under local unitary transformations
of three-qubit pure states are analyzed. The interconvertibility, symmetry
properties, parameter ranges, calculability and behavior under measurement are
looked at. It is shown that the entanglement monotones of any multipartite pure
state uniquely determine the orbit of that state under local unitary
transformations. It follows that there must be an entanglement monotone for
three-qubit pure states which depends on the Kempe invariant defined in [Phys.
Rev. A 60, 910 (1999)]. A form for such an entanglement monotone is proposed. A
theorem is proved that significantly reduces the number of entanglement
monotones that must be looked at to find the maximal probability of
transforming one multipartite state to another.Comment: 14 pages, REVTe
Hubungan Antara Produsen Dan Konsumen: Sebuah Tinjauan Etis
The purpose of this article is to provide an ethical foundation for relationshipmarketing using a virtue ethics approach. A phrase: âThe customer is a kingâ means thecustomer is essential to the welfare of the business. On one hand, buyer and seller have ashared interest in âdoing the dealâ. They want to do business with each other, and bothbenefit from the transaction. On the other hand, every rupiah a buyer saves is a rupiah lostfrom the seller\u27s point of view. Every buyer wants a low price and every seller wants a highprice. So, if fairness is good, then we should promote fairness in commercial transactions, justas we do in other areas of life. And that requires that buyer and seller at least see each otheras equals
A paradox in bosonic energy computations via semidefinite programming relaxations
We show that the recent hierarchy of semidefinite programming relaxations
based on non-commutative polynomial optimization and reduced density matrix
variational methods exhibits an interesting paradox when applied to the bosonic
case: even though it can be rigorously proven that the hierarchy collapses
after the first step, numerical implementations of higher order steps generate
a sequence of improving lower bounds that converges to the optimal solution. We
analyze this effect and compare it with similar behavior observed in
implementations of semidefinite programming relaxations for commutative
polynomial minimization. We conclude that the method converges due to the
rounding errors occurring during the execution of the numerical program, and
show that convergence is lost as soon as computer precision is incremented. We
support this conclusion by proving that for any element p of a Weyl algebra
which is non-negative in the Schrodinger representation there exists another
element p' arbitrarily close to p that admits a sum of squares decomposition.Comment: 22 pages, 4 figure
Noisy metrology beyond the standard quantum limit
Parameter estimation is of fundamental importance in areas from atomic
spectroscopy and atomic clocks to gravitational wave detection. Entangled
probes provide a significant precision gain over classical strategies in the
absence of noise. However, recent results seem to indicate that any small
amount of realistic noise restricts the advantage of quantum strategies to an
improvement by at most a multiplicative constant. Here, we identify a relevant
scenario in which one can overcome this restriction and attain superclassical
precision scaling even in the presence of uncorrelated noise. We show that
precision can be significantly enhanced when the noise is concentrated along
some spatial direction, while the Hamiltonian governing the evolution which
depends on the parameter to be estimated can be engineered to point along a
different direction. In the case of perpendicular orientation, we find
superclassical scaling and identify a state which achieves the optimum.Comment: Erroneous expressions with inconsistent units have been corrected. 5
pages, 3 figures + Appendi
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