309 research outputs found
Non-Markovianity in a collision model with environmental block
We present an extended collision model to simulate the dynamics of an open
quantum system. In our model, the unit to represent the environment is, instead
of a single particle, a block which consists of a number of environment
particles. The introduced blocks enable us to study the effects of different
strategies of system-environment interactions and states of the blocks on the
non-Markovianities. We demonstrate our idea in the Gaussian channels of an
all-optical system and derive a necessary and sufficient condition of
non-Markovianity for such channels. Moreover, we show the equivalence of our
criterion to the non-Markovian quantum jump in the simulation of the pure
damping process of a single-mode field. We also show that the non-Markovianity
of the channel working in the strategy that the system collides with
environmental particles in each block in a certain order will be affected by
the size of the block and the embedded entanglement and the effects of heating
and squeezing the vacuum environmental state will quantitatively enhance the
non-Markovianity.Comment: 9 pages, 6 figures, accepted versio
Direct Measure of Quantum Correlation
The quantumness of the correlation known as quantum correlation is usually
measured by quantum discord. So far various quantum discords can be roughly
understood as indirect measure by some special discrepancy of two quantities.
We present a direct measure of quantum correlation by revealing the difference
between the structures of classically and quantum correlated states. Our
measure explicitly includes the contributions of the inseparability and local
non-orthogonality of the eigenvectors of a density. Besides its relatively easy
computability, our measure can provide a unified understanding of quantum
correlation of all the present versions
The Roles of a Quantum Channel on a Quantum State
When a quantum state undergoes a quantum channel, the state will be
inevitably influenced. In general, the fidelity of the state is reduced, so is
the entanglement if the sub- systems go through the channel. However, the
influence on the coherence of the state is quite different. Here we present
some state-independent quantities to describe to what degree the fidelity, the
entanglement and the coherence of the state are influenced. As applications, we
consider some quantum channels on a qubit and find that the infidelity ability
monotonically depends on the decay rate, but in usual the decoherence ability
is not the case and strongly depends on the channel.Comment: 12 pages, 1 figur
Bipartite concurrence and localized coherence
Based on a proposed coherence measure, we show that the local coherence of a
bipartite quantum pure state (coherence of its reduced density matrix) is
exactly the same as the minimal average co- herence with all potential
pure-state realizations under consideration. In particular, it is shown that
bipartite concurrence of pure states just captures the maximal difference
between local coherence and the average coherence of one subsystem induced by
local operations on the other subsystem with the assistance of classical
communications, which provides an alternative operational meaning for bipartite
concurrence of pure states. The relation between concurrence and the proposed
coherence measure can also be extended to bipartite mixed states.Comment: 6 pages, 0 figure
Separability Criteria For Arbitrary Quantum Systems
The purpose of this paper is to obtain a sufficient and necessary condition
as a criteria to test whether an arbitrary multipartite state is entangled or
not. Based on the tensor expression of a multipartite pure state, the paper
shows that a state is separable iff =0 for pure states
and iff vanishes for mixed states.Comment: 4 pages, 1 figure
A type of localized quadripartite entanglement
In this paper, we show that the average three-tangle of the reduced
tripartite density matrix for some quadripartite pure states can be increased
by some potential measurements on the fourth subsystem, which means this type
of quadripartite entanglement can be localized. In particular, we prove that
the maximal increment with all potential measurements taken into account is a
quadripartite entanglement monotone, so it quantifies this localized
quadripartite entanglement. By analyzing quadripartite pure states based on the
previous classification, we find that this quadripartite entanglement monotone
is not only present in the standard GHZ state and absent in the standard W
states. In addition, based on the proposed entanglement measure, we construct a
new monogamy relation.Comment: 5 pages. (A tough version before publication
Re-examining the self-contained quantum refrigerator in the strong-coupling regime
We revisit the self-contained quantum refrigerator in the
strong-internal-coupling regime by employing the quantum optical master
equation. It is shown that strong internal coupling reduces the cooling ability
of the refrigerator. In contrast to the weak-coupling case, strong internal
coupling could lead to quite different and even converse thermodynamic
behaviors.Comment: 5 pages, 6 figures, Physical Review E 90, 052142 (2014
The precision of parameter estimation for dephasing model under squeezed reservoir
We study the precision of parameter estimation for dephasing model under
squeezed environment. We analytically calculate the dephasing factor
and obtain the analytic quantum Fisher information (QFI) for the
amplitude parameter and the phase parameter . It is shown that
the QFI for the amplitude parameter is invariant in the whole process,
while the QFI for the phase parameter strongly depends on the reservoir
squeezing. It is shown that the QFI can be enhanced for appropriate squeeze
parameters and . Finally, we also investigate the effect of
temperature on the QFI
Generalized Bell inequality for mixed states with variable constraints
In this paper, we present a generalized Bell inequality for mixed states. The
distinct characteristic is that the inequality has variable bound depending on
the decomposition of the density matrix. The inequality has been shown to be
more refined than the previous Bell inequality. It is possible that a separable
mixed state can violate the Bell inequality.Comment: 5 pages and 3 figures, Comments and suggestion are expected and
welcom
Describing a Quantum Channel by State Tomography of a Single Probe State
A general law is presented for (composite) quantum systems which directly
describes the time evolution of quantum states (with one or both components)
through an arbitrary noisy quantum channel. It is shown that the time evolution
of all quantum states through a quantum channel can be completely captured by
the evolution of a single 'probe state'. Thus in order to grasp the information
of the final output states subject to a quantum channel, especially an unknown
one, it only requires quantum state tomography of a single probe state, which
dramatically simplifies the practical operations in experiment.Comment: 3 pages, To be publised in EP
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