A paradigm for entanglement and information swapping of two qubits (original) (raw)
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Interplay between entanglement and entropy in two-qubit systems
Journal of Physics B: Atomic, Molecular and Optical Physics, 2010
We study the exact entanglement dynamics of two qubits interacting with a common zerotemperature non-Markovian reservoir. We consider the two qubits initially prepared in Bell-like states or extended Werner-like states. We study the dependence of the entanglement dynamics on both the degree of purity and the amount of entanglement of the initial state. We also explore the relation between the entanglement and the von Neumann entropy dynamics and find that these two quantities are correlated for initial Bell-like states.
Dynamics of Entanglement In Two Coupled Qubits
Arxiv preprint cond-mat/0312145, 2003
Considerable progress has been made in understanding how dissipation drives the state of a single qubit from a quantum-mechanical superposition to a classical mixed state. This paper uses a Bloch-Redfield approach to study how, in a system of two qubits, dissipation drives the bipartite state of the two qubits from an entangled state to a product state. The measure used for mixed-state entanglement is Wootters's formula for the entanglement of formation. For qubits that start in an entangled state and are then decoupled, entanglement is found to decay faster in general than the decoherence of single qubit states by a factor 2/ log 2 that can be obtained analytically in a limiting case. We show that the dynamics of entanglement for realistic parameters is different from that of fidelity: for some experimental parameters a bipartite state loses fidelity much more rapidly than it loses entanglement. These results are of some practical interest since entanglement is thought to be the essential "fuel" for fast quantum algorithms.
Dynamics of quantum entanglement
Physical Review A, 2002
A model of discrete dynamics of entanglement of bipartite quantum state is considered. It involves a global unitary dynamics of the system and periodic actions of local bistochastic or decaying channel. For initially pure states the decay of entanglement is accompanied with an increase of von Neumann entropy of the system. We observe and discuss revivals of entanglement due to unitary interaction of subsystems. For some mixed states having different marginal entropies of the subsystems we find an asymmetry in speed of entanglement decay. The entanglement of these states decreases faster, if the depolarizing channel acts on the "classical" subsystem, characterized by smaller marginal entropy.
Entanglement dynamics of two-bipartite system under the influence of dissipative environments
Optics Communications, 2010
An experimental scheme is suggested that permits a direct measure of entanglement of two-qubit cavity system. It is articulated on the cavity-QED technology utilizing atoms as flying qubits. With this scheme we generate two different measures of entanglement namely logarithmic negativity and concurrence. The phenomenon of sudden death entanglement (ESD) in a bipartite system subjected to dissipative environment will be examined.
Physical Review Letters, 2012
The dynamics of the environment is usually experimentally inaccessible and hence ignored for open systems. Here we overcome this limitation by using an interferometric setup that allows the implementation of several decoherence channels and full access to all environmental degrees of freedom. We show that when a qubit from an entangled pair interacts with the environment, the initial bipartite entanglement gets redistributed into bipartite and genuine multipartite entanglements involving the two qubits and the environment. This is yet another trait of the subtle behavior of entangled open systems.
Exact dynamics of entanglement and entropy in structured environments
2009
We study the exact entanglement dynamics of two qubits interacting with a common zero-temperature non-Markovian reservoir. We consider the two qubits initially prepared in Bell-like states or extended Werner-like states. We study the dependence of the entanglement dynamics on both the degree of purity and the amount of entanglement of the initial state. We also explore the relation between the
Entanglement dynamics of two independent qubits in environments with and without memory
Physical Review A, 2008
A procedure to obtain the dynamics of NNN independent qudits ($d$-level systems) each interacting with its own reservoir, for any arbitrary initial state, is presented. This is then applied to study the dynamics of the entanglement of two qubits, initially in an extended Werner-like mixed state with each of them in a zero temperature non-Markovian environment. The dependence of the entanglement dynamics on the purity and degree of entanglement of the initial states and on the amount of non-Markovianity is also given. This extends the previous work about non-Markovian effects on the two-qubit entanglement dynamics for initial Bell-like states [B. Bellomo \textit{et al.}, Phys. Rev. Lett. \textbf{99}, 160502 (2007)]. The effect of temperature on the two-qubit entanglement dynamics in a Markovian environment is finally obtained.
Quantum entanglement and entropy
Physical Review A, 2001
Entanglement is the fundamental quantum property behind the now popular field of quantum transport of information. This quantum property is incompatible with the separation of a single system into two uncorrelated subsystems. Consequently, it does not require the use of an additive form of entropy. We discuss the problem of the choice of the most convenient entropy indicator, focusing our attention on a system of 2 qubits, and on a special set, denoted by ℑ. This set contains both the maximally and the partially entangled states that are described by density matrices diagonal in the Bell basis set. We select this set for the main purpose of making more straightforward our work of analysis. As a matter of fact, we find that in general the conventional von Neumann entropy is not a monotonic function of the entanglement strength. This means that the von Neumann entropy is not a reliable indicator of the departure from the condition of maximum entanglement. We study the behavior of a form of non-additive entropy, made popular by the 1988 work by Tsallis. We show that in the set ℑ, implying the key condition of non-vanishing entanglement, this non-additive entropy indicator turns out
Journal of Physics A: Mathematical and Theoretical, 2010
We explore various aspects of the quantum entanglement dynamics of systems of two, three and four qubits interacting with an environment at zero temperature in a non-Markovian regime, as described by the paradigmatic model recently studied by Bellomo, Lo Franco, and Compagno [Bellomo et al. Phys. Rev. Lett. 99 (2007) 160502]. We consider important families of initial states for the alluded systems. The average, typical entanglement evolution associated with each of these families is determined, and its relation with the evolution of the global degree of mixedness of the multi-qubit system is explored. For three and four qubits we consider the family of initial states equivalent under local unitary transformations to the |GHZ and |W states, and compare their average behavior with the average behavior exhibited by initial maximally entangled twoqubits states. Furthermore, in the case of two qubits, the evolution of other manifestations of entanglement, related to measurable quantities, is also investigated. In particular, we consider the Mintert-Buchleitner concurrence lower bound and an entanglement indicator based upon the violation of local uncertainty relations.