370 research outputs found
Quantum Coherence via Skew Information and Its Polygamy
Quantifying coherence is a key task in both quantum mechanical theory and
practical applications. Here, a reliable quantum coherence measure is presented
by utilizing the quantum skew information of the state of interest subject to a
certain broken observable. This coherence measure is proven to fulfill all the
criteria (especially the strong monotonicity) recently introduced in the
resource theories of quantum coherence. The coherence measure has an analytic
expression and an obvious operational meaning related to quantum metrology. In
terms of this coherence measure, the distribution of the quantum coherence,
i.e., how the quantum coherence is distributed among the multiple parties is
studied and a corresponding polygamy relation is proposed. As a further
application, it is found that the coherence measure forms the natural upper
bounds for quantum correlations prepared by incoherent operations. The
experimental measurement of our coherence measure as well as the
relative-entropy coherence, -norm coherence is studied finally.Comment: 14 pages, 4 figures; accepted by PR
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
Remedying the strong monotonicity of the coherence measure in terms of the Tsallis relative entropy
Coherence is the most fundamental quantum feature of the nonclassical
systems. The understanding of coherence within the resource theory has been
attracting increasing interest among which the quantification of coherence is
an essential ingredient. A satisfactory measure should meet certain standard
criteria. It seems that the most crucial criterion should be the strong
monotonicity, that is, average coherence doesn't increase under the
(sub-selective) incoherent operations. Recently, the Tsallis relative
entropy [A. E. Rastegin, Phys. Rev. A \textbf{93}, 032136 (2016)] has been
tried to quantify the coherence. But it was shown to violate the strong
monotonicity, even though it can unambiguously distinguish the coherent and the
incoherent states with the monotonicity. Here we establish a family of
coherence quantifiers which are closely related to the Tsallis relative entropy. It proves that this family of quantifiers satisfy all the standard
criteria and particularly cover several typical coherence measures.Comment: 6 page
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
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
Entanglement Monogamy of Tripartite Quantum States
An interesting monogamy equation with the form of Pythagorean theorem is
found for -dimensional pure states, which reveals the
relation among bipartite concurrence, concurrence of assistance, and genuine
tripartite entanglement. At the same time, a genuine tripartite entanglement
monotone as a generalization of 3-tangle is naturally obtained for - dimensional pure states in terms of a distinct idea. For mixed
states, the monogamy equation is reduced to a monogamy inequality. Both results
for tripartite quantum states can be employed to multipartite quantum states.Comment: 5 pages, 1 figur
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
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