Dresden 2011 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 20: Quantum Information: Concepts and Methods 3
Q 20.7: Talk
Tuesday, March 15, 2011, 12:00–12:15, SCH A118
Robust and Fragile Entanglement in Qubit Environments — •Jaroslav Novotny1,2, Gernot Alber1, and Igor Jex2 — 1Institut für Angewandte Physik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany — 2Department of Physics, FNSPE CTU in Prague, Czech Republic
The asymptotic decoherence originating from iteratively applied random unitary couplings between distinguishable qubits of a quantum network is investigated. Within this framework the resulting asymptotic dynamics of a subsystem and its residual qubit environment is explored without any further simplifying assumptions concerning the coupling strength or the number of relevant couplings between subsystem and its environment or the numbers of qubits involved. The dependence of the resulting asymptotic decoherence and entanglement decay of the subsystem on the interaction topology and on the size and initial state of the environment is discussed. It is shown that there are two classes of entangled states whose asymptotic entanglement decay depends on the size of the surrounding qubit environment in a characteristic and completely different way. The asymptotic entanglement of members of the first class is destroyed already for a finite and usually very small number of environmental qubits. Besides this class of fragile entangled states there is also the second class of robustly entangled states whose entanglement is not destroyed completely for any finite size of the surrounding qubit environment. A simple analytical criterion is presented which is capable of distinguishing between these two classes in the case of two-qubit states.