24 research outputs found
Universal quantum Controlled-NOT gate
An investigation of an optimal universal unitary Controlled-NOT gate that
performs a specific operation on two unknown states of qubits taken from a
great circle of the Bloch sphere is presented. The deep analogy between the
optimal universal C-NOT gate and the `equatorial' quantum cloning machine (QCM)
is shown. In addition, possible applications of the universal C-NOT gate are
briefly discussed.Comment: 18 reference
Quantum computing with mixed states
We discuss a model for quantum computing with initially mixed states.
Although such a computer is known to be less powerful than a quantum computer
operating with pure (entangled) states, it may efficiently solve some problems
for which no efficient classical algorithms are known. We suggest a new
implementation of quantum computation with initially mixed states in which an
algorithm realization is achieved by means of optimal basis independent
transformations of qubits.Comment: 2 figures, 52 reference
Entanglement dynamics of three-qubit states in noisy channels
We study entanglement dynamics of the three-qubit system which is initially
prepared in pure Greenberger-Horne- Zeilinger (GHZ) or W state and transmitted
through one of the Pauli channels or the
depolarizing channel. With the help of the lower bound for three-qubit
concurrence we show that the W state preserves more entanglement than the GHZ
state in transmission through the Pauli channel . For the Pauli
channels and the depolarizing channel, however, the
entanglement of the GHZ state is more resistant against decoherence than the
W-type entanglement. We also briefly discuss how the accuracy of the lower
bound approximation depends on the rank of the density matrix under
consideration.Comment: 2 figures, 32 reference
Quantum discord evolution of three-qubit states under noisy channels
We investigated the dissipative dynamics of quantum discord for correlated
qubits under Markovian environments.
The basic idea in the present scheme is that quantum discord is more general,
and possibly more robust and fundamental, than entanglement. We provide three
initially correlated qubits in pure Greenberger-Horne-Zeilinger (GHZ) or W
state and analyse the time evolution of the quantum discord under various
dissipative channels such as:
Pauli channels , , and , as well as
depolarising channels. Surprisingly, we find that under the action of Pauli
channel , the quantum discord of GHZ state is not affected by
decoherence. For the remaining dissipative channels, the W state is more robust
than the GHZ state against decoherence. Moreover, we compare the dynamics of
entanglement with that of the quantum discord under the conditions in which
disentanglement occurs and show that quantum discord is more robust than
entanglement except for phase flip coupling of the three qubits system to the
environment.Comment: 17 pages, 4 figures, accepted for publication in EPJ