22,237 research outputs found
Quantum entanglement in photosynthetic light harvesting complexes
Light harvesting components of photosynthetic organisms are complex, coupled,
many-body quantum systems, in which electronic coherence has recently been
shown to survive for relatively long time scales despite the decohering effects
of their environments. Within this context, we analyze entanglement in
multi-chromophoric light harvesting complexes, and establish methods for
quantification of entanglement by presenting necessary and sufficient
conditions for entanglement and by deriving a measure of global entanglement.
These methods are then applied to the Fenna-Matthews-Olson (FMO) protein to
extract the initial state and temperature dependencies of entanglement. We show
that while FMO in natural conditions largely contains bipartite entanglement
between dimerized chromophores, a small amount of long-range and multipartite
entanglement exists even at physiological temperatures. This constitutes the
first rigorous quantification of entanglement in a biological system. Finally,
we discuss the practical utilization of entanglement in densely packed
molecular aggregates such as light harvesting complexes.Comment: 14 pages, 7 figures. Improved presentation, published versio
Operational one-to-one mapping between coherence and entanglement measures
We establish a general operational one-to-one mapping between coherence
measures and entanglement measures: Any entanglement measure of bipartite pure
states is the minimum of a suitable coherence measure over product bases. Any
coherence measure of pure states, with extension to mixed states by convex
roof, is the maximum entanglement generated by incoherent operations acting on
the system and an incoherent ancilla. Remarkably, the generalized CNOT gate is
the universal optimal incoherent operation. In this way, all convex-roof
coherence measures, including the coherence of formation, are endowed with
(additional) operational interpretations. By virtue of this connection, many
results on entanglement can be translated to the coherence setting, and vice
versa. As applications, we provide tight observable lower bounds for
generalized entanglement concurrence and coherence concurrence, which enable
experimentalists to quantify entanglement and coherence of the maximal
dimension in real experiments.Comment: 14 pages, 1 figure, new results added, published in PR
Maximal Entanglement of Two-qubit States Constructed by Linearly Independent Coherent States
In this paper, we find the necessary and sufficient condition for the maximal
entanglement of the state, constructed by linearly independent
coherent states with \emph{real parameters} when
. This is a further generalization of the
classified nonorthogonal states discussed in Ref. Physics Letters A {\bf{291}},
73-76 (2001).Comment: some examples added; Int J Theor Phys 201
Relations between entanglement and purity in non-Markovian dynamics
Knowledge of the relationships among different features of quantumness, like
entanglement and state purity, is important from both fundamental and practical
viewpoints. Yet, this issue remains little explored in dynamical contexts for
open quantum systems. We address this problem by studying the dynamics of
entanglement and purity for two-qubit systems using paradigmatic models of
radiation-matter interaction, with a qubit being isolated from the environment
(spectator configuration). We show the effects of the corresponding local
quantum channels on an initial two-qubit pure entangled state in the
concurrence-purity diagram and find the conditions which enable dynamical
closed formulas of concurrence, used to quantify entanglement, as a function of
purity. We finally discuss the usefulness of these relations in assessing
entanglement and purity thresholds which allow noisy quantum teleportation. Our
results provide new insights about how different properties of composite open
quantum systems behave and relate each other during quantum evolutions.Comment: 16 Pages, 10 Figures. One author added. Improved version with more
references and comment
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