83,082 research outputs found
On Reduced Time Evolution for Initially Correlated Pure States
A new method to deal with reduced dynamics of open systems by means of the
Schr\"odinger equation is presented. It allows one to consider the reduced time
evolution for correlated and uncorrelated initial conditions.Comment: accepted in Open Sys. Information Dy
Negativity and quantum discord in Davies environments
We investigate the time evolution of negativity and quantum discord for a
pair of non-interacting qubits with one being weakly coupled to a decohering
Davies--type Markovian environment. At initial time of preparation, the qubits
are prepared in one of the maximally entangled pure Bell states. In the
limiting case of pure decoherence (i.e. pure dephasing), both, the quantum
discord and negativity decay to zero in the long time limit. In presence of a
manifest dissipative dynamics, the entanglement negativity undergoes a sudden
death at finite time while the quantum discord relaxes continuously to zero
with increasing time. We find that in dephasing environments the decay of the
negativity is more propitious with increasing time; in contrast, the evolving
decay of the quantum discord proceeds weaker for dissipative environments.
Particularly, the slowest decay of the quantum discord emerges when the energy
relaxation time matches the dephasing time.Comment: submitted for publicatio
Physically Realizable Entanglement by Local Continuous Measurements
Quantum systems prepared in pure states evolve into mixtures under
environmental action. Physically realizable ensembles are the pure state
decompositions of those mixtures that can be generated in time through
continuous measurements of the environment. Here, we define physically
realizable entanglement as the average entanglement over realizable ensembles.
We optimize the measurement strategy to maximize and minimize this quantity
through local observations on the independent environments that cause two
qubits to disentangle in time. We then compare it with the entanglement bounds
for the unmonitored system. For some relevant noise sources the maximum
realizable entanglement coincides with the upper bound, establishing the scheme
as an alternative to locally protect entanglement. However, for local
strategies, the lower bound of the unmonitored system is not reached.Comment: version 2; 5 pages, 1 figure; added references
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