293 research outputs found
Factorization and Criticality in the Anisotropic XY Chain via Correlations
In this review, we discuss the zero and finite temperature behavior of
various bipartite quantum and total correlation measures, the skew
information-based quantum coherence, and the local quantum uncertainty in the
thermal ground state of the one-dimensional anisotropic XY model in transverse
magnetic field. We compare the ability of considered measures to correctly
detect or estimate the quantum critical point and the non-trivial factorization
point possessed by the spin chain.Comment: 29 pages, 8 figures. A review paper accepted for publication in the
special issue Entanglement Entropy in the journal Entrop
Conservation law for distributed entanglement of formation and quantum discord
We present a direct relation, based upon a monogamic principle, between
entanglement of formation (EOF) and quantum discord (QD), showing how they are
distributed in an arbitrary tripartite pure system. By extending it to a
paradigmatic situation of a bipartite system coupled to an environment, we
demonstrate that the EOF and the QD obey a conservation relation. By means of
this relation we show that in the deterministic quantum computer with one pure
qubit the protocol has the ability to rearrange the EOF and the QD, which
implies that quantum computation can be understood on a different basis as a
coherent dynamics where quantum correlations are distributed between the qubits
of the computer. Furthermore, for a tripartite mixed state we show that the
balance between distributed EOF and QD results in a stronger version of the
strong subadditivity of entropy.Comment: Published versio
Robustness of quantum discord to sudden death
We calculate the dissipative dynamics of two-qubit quantum discord under
Markovian environments. We analyze various dissipative channels such as
dephasing, depolarizing, and generalized amplitude damping, assuming
independent perturbation, in which each qubit is coupled to its own channel.
Choosing initial conditions that manifest the so-called sudden death of
entanglement, we compare the dynamics of entanglement with that of quantum
discord. We show that in all cases where entanglement suddenly disappears,
quantum discord vanishes only in the asymptotic limit, behaving similarly to
individual decoherence of the qubits, even at finite temperatures. Hence,
quantum discord is more robust than the entanglement against to decoherence so
that quantum algorithms based only on quantum discord correlations may be more
robust than those based on entanglement.Comment: 4 figures, 4 page
Protecting the operation from general and residual errors by continuous dynamical decoupling
We study the occurrence of errors in a continuously decoupled two-qubit state
during a quantum operation under decoherence. We consider a
realization of this quantum gate based on the Heisenberg exchange interaction,
which alone suffices for achieving universal quantum computation. Furthermore,
we introduce a continuous-dynamical-decoupling scheme that commutes with the
Heisenberg Hamiltonian to protect it from the amplitude damping and dephasing
errors caused by the system-environment interaction. We consider two
error-protection settings. One protects the qubits from both amplitude damping
and dephasing errors. The other features the amplitude damping as a residual
error and protects the qubits from dephasing errors only. In both settings, we
investigate the interaction of qubits with common and independent environments
separately. We study how errors affect the entanglement and fidelity for
different environmental spectral densities.Comment: Extended version of arXiv:1005.1666. To appear in PR
- …