5,020 research outputs found
Robustness of Highly Entangled Multi-Qubit States Under Decoherence
We investigate the decay of entanglement, due to decoherence, of multi-qubit
systems that are initially prepared in highly (in some cases maximally)
entangled states. We assume that during the decoherence processes each qubit of
the system interacts with its own, independent environment. We determine, for
systems with a small number of qubits and for various decoherence channels, the
initial states exhibiting the most robust entanglement. We also consider a
restricted version of this robustness optimization problem, only involving
states equivalent under local unitary transformations to the |GHZ> state.Comment: 16 pages, 3 figures. Changes in Sec.
The Mariner 5 flight path and its determination from tracking data
Mariner 5 flight path and its determination from tracking dat
Efficient generation of random multipartite entangled states using time optimal unitary operations
We review the generation of random pure states using a protocol of repeated
two qubit gates. We study the dependence of the convergence to states with Haar
multipartite entanglement distribution. We investigate the optimal generation
of such states in terms of the physical (real) time needed to apply the
protocol, instead of the gate complexity point of view used in other works.
This physical time can be obtained, for a given Hamiltonian, within the
theoretical framework offered by the quantum brachistochrone formalism. Using
an anisotropic Heisenberg Hamiltonian as an example, we find that different
optimal quantum gates arise according to the optimality point of view used in
each case. We also study how the convergence to random entangled states depends
on different entanglement measures.Comment: 5 pages, 2 figures. New title, improved explanation of the algorithm.
To appear in Phys. Rev.
A genuine maximally seven-qubit entangled state
Contrary to A.Borras et al.'s [1] conjecture, a genuine maximally seven-qubit
entangled state is presented. We find a seven-qubit state whose marginal
density matrices for subsystems of 1,2- qubits are all completely mixed and for
subsystems of 3-qubits is almost completely mixed
Multi-Qubit Systems: Highly Entangled States and Entanglement Distribution
A comparison is made of various searching procedures, based upon different
entanglement measures or entanglement indicators, for highly entangled
multi-qubits states. In particular, our present results are compared with those
recently reported by Brown et al. [J. Phys. A: Math. Gen. 38 (2005) 1119]. The
statistical distribution of entanglement values for the aforementioned
multi-qubit systems is also explored.Comment: 24 pages, 3 figure
Brachistochrone of Entanglement for Spin Chains
We analytically investigate the role of entanglement in time-optimal state
evolution as an appli- cation of the quantum brachistochrone, a general method
for obtaining the optimal time-dependent Hamiltonian for reaching a target
quantum state. As a model, we treat two qubits indirectly cou- pled through an
intermediate qubit that is directly controllable, which represents a typical
situation in quantum information processing. We find the time-optimal unitary
evolution law and quantify residual entanglement by the two-tangle between the
indirectly coupled qubits, for all possible sets of initial pure quantum states
of a tripartite system. The integrals of the motion of the brachistochrone are
determined by fixing the minimal time at which the residual entanglement is
maximized. Entan- glement plays a role for W and GHZ initial quantum states,
and for the bi-separable initial state in which the indirectly coupled qubits
have a nonzero value of the 2-tangle.Comment: 9 pages, 4 figure
Generalized Criterion of Maximally Multi-Qubit Entanglement
We first present a generalized criterion for maximally entangled states of 2,
3, 4, 5, 6, 8 and in theory to arbitrary-number qubits. By this criterion, some
known highly entangled multi-qubit states are examined and a new genuine
eight-qubit maximally entangle state is obtained. For the 4, 7 and 8 qubits
system in which no maximally multi-qubit entangled states (MMES) is thought to
exist before, we find that the proved and most suspected MMESes, are not
completely mixed in subsystem with a critical-number qubits, below which the
subsystems are all completely mixed. We believe that the new criterion and MMES
can play important role in quantum information technology, such as the
teleportation and dense coding
Quantum teleportation and state sharing using a genuinely entangled six qubit state
The usefulness of the genuinely entangled six qubit state that was recently
introduced by Borras et al. is investigated for the quantum teleportation of an
arbitrary three qubit state and for quantum state sharing (QSTS) of an
arbitrary two qubit state. For QSTS, we explicitly devise two protocols and
construct sixteen orthogonal measurement basis which can lock an arbitrary two
qubit information between two parties.Comment: 6 pages, 7 table
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