8 research outputs found
Symmetrization and Entanglement of Arbitrary States of Qubits
Given two arbitrary pure states and of qubits or higher
level states, we provide arguments in favor of states of the form instead of symmetric or
anti-symmetric states, as natural candidates for optimally entangled states
constructed from these states. We show that such states firstly have on the
average a high value of concurrence, secondly can be constructed by a universal
unitary operator independent of the input states. We also show that these
states are the only ones which can be produced with perfect fidelity by any
quantum operation designed for intertwining two pure states with a relative
phase. A probabilistic method is proposed for producing any pre-determined
relative phase into the combination of any two arbitrary states.Comment: 6 pages, 1 figur
Quantum dense coding by spatial state entanglement
We have presented a theoretical extended version of dense coding protocol
using entangled position state of two particles shared between two parties. A
representation of Bell states and the required unitary operators are shown
utilizing symmetric normalized Hadamard matrices. In addition, some explicit
and conceivable forms for the unitary operators are presented by using some
introduced basic operators. It is shown that, the proposed version is
logarithmically efficient than some other multi-qubit dense coding protocols.Comment: 4 pages, 1 figure, Revte
On a suggestion relating topological and quantum mechanical entanglements
We analyze a recent suggestion \cite{kauffman1,kauffman2} on a possible
relation between topological and quantum mechanical entanglements. We show that
a one to one correspondence does not exist, neither between topologically
linked diagrams and entangled states, nor between braid operators and quantum
entanglers. We also add a new dimension to the question of entangling
properties of unitary operators in general.Comment: RevTex, 7 eps figures, to be published in Phys. Lett. A (2004
Separability in Asymmetric Phase-Covariant Cloning
Here, asymmetric phase-covariant quantum cloning machines are defined and
trade-off between qualities of their outputs and its impact on entanglement
properties of the outputs are studies. In addition, optimal families among
these cloners are introduced and also their entanglement properties are
investigated. An explicit proof of optimality is presented for the case of
qubits, which is based on the no-signaling condition. Our optimality proof can
also be used to derive an upper bound on trade-off relations for a more general
class of optimal cloners which clone states on a specific orbit of the Bloch
sphere. It is shown that the optimal cloners of the equatorial states, as in
the case of symmetric phase-covariant cloning, give rise to two separable
clones, and in this sense these states are unique. For these cloners it is
shown that total output is of GHZ-type
Distributed phase-covariant cloning with atomic ensembles via quantum Zeno dynamics
We propose an interesting scheme for distributed orbital state quantum
cloning with atomic ensembles based on the quantum Zeno dynamics. These atomic
ensembles which consist of identical three-level atoms are trapped in distant
cavities connected by a single-mode integrated optical star coupler. These
qubits can be manipulated through appropriate modulation of the coupling
constants between atomic ensemble and classical field, and the cavity decay can
be largely suppressed as the number of atoms in the ensemble qubits increases.
The fidelity of each cloned qubit can be obtained with analytic result. The
present scheme provides a new way to construct the quantum communication
network.Comment: 5 pages, 4 figure