Decoherence, Entanglement and Information Protection in Complex Quantum Systems

Dynamics of an open system interacting with theenvironment considered as a thermostate may be formulatedin terms of a master equation with an integral operator allowing for the relaxation process, [Zwanzig 1960]. In some part- ular cases this operator hasashort-lastingkernel that enables one to consider therelaxation as a Markovian process and to obtainthe master equation inthe Lindblad form, [Lindblad 1976 (a)]. In some situations the memory effects become, however, important and the dynamics of thesystem gets much more involved, [Barnett 2001]. A similar situation arises inthe case where a set of consecutive or continuous measurements is performed. The purpose of this article is to consider a situation where some simplification of the generalform of the master equation with memory isstill possibleand the result isasimpler master equation. In particular, we consider the case of a dynamic system c- pled to a measured ancilla via a nondemolition interaction, [Caves 1980]. This simplifies the consideration essentiallywhereas providing an important special case inwhich the energy of the dynamic part is conserved. We consider a composite quantum system consisting of a dynamic part - teracting with an ancillary part, the latter being subject to repeated projective measurements. The entire quantum system is assumed to evolve unitarily d- ing time ? t between the measurements. As a specific example, we analyze a harmonic oscillator coupledtoatwo-level ancillathat issubject to measu- ments.

Acknowledgments,Editorial article; V. M. Akulin et al. Part I Role of entanglement in quantum computing and information processing. Quantum ensembles and quantum informatics ; V. M. Akuli et al.,Entanglement in quantum information processing ; S. L. Braunstein. ,Easy control over fermionic computations;Y. Ozhigov.. Part II Multiatom and multiphoton entanglement. Multiatom and multiphoton entanglement; D. Petrosya et al.,On the advanced wave model of parametric down-conversion; A. I. Lvovsky and T. Aichele. .Quantum logics based on four-photon entanglement; Ph. Walther and A. Zeilinger. Towards quantum control of light; L. I. Childress et al. Deterministic entanglement of single photons; D. Petrosyan. Selective control of high-order atomic coherences; Yu. P. Malakyan et al. Strong entanglement of bright light beams in controlled quantum systems; G. Yu. Kryuchkyan and H. H. Adamyan. Part III Adiabatic and nonadiabatic protection from Decoherence. Adiabatic and nonadiabatic protection from decoherence; S. Pellegrin et al. Coherence protection by the quantum Zeno effect; E. Brion et al. Implementation of protected qubits by Josephson junction arrays; L. B. Ioffe. Coherence protection near energy gaps; C. Mewes et al. Zeno and anti-Zeno dynamics; G. Kurizki et al. Part IV Non-Markovian decay and decoherence in open quantum systems. Non-Markovian decay and decoherence in open quantum systems; J. Salo et al. The varieties of Master Equations; J. Salo et al. Quantum dynamics effected by repeated measurements; J. Clausen et al. Motional damping of impurity atoms in Bose-Einstein condensates; I. E. Mazets and G. Kurizki. Part V Internal-translational entanglement and interference in atoms and molecules. Internal-translational entanglement and interference in atoms and molecules; T. Opatrn et al. Atom-mesoscopic field entanglement S. Haroch et al. Coherence and decoherence experiments with fullerenes, M. Arnd et al. Distant entanglement of macroscopic gassamples; J. Sherson et al. Entanglement in optical lattices; T. Opatrn et al. Investigation of Autler-Townes effect in sodium dimmers; R. Garcia-Fernande et al. Transition steering via space-dependent coupling; M. Leibscher and S. Stenholm.Coherence and decoherence in Rydberg gases; P. Pillet et al. Part VI Proton entanglement and decoherence in solids. Schrödinger’s cat states of protons in condensed matter; M. Krzystynia et al. Anomalous neutron inelastic cross sections at eV energy transfers; J. Mayers and T. Abdul-Redah. Quantum entanglement and decoherence due to electrons-protons coupling; T. Abdul-Redah et al. Attosecond effects in scattering of neutrons and electrons from protons; C. A. Chatzidimitriou-Dreismann et al. Macroscopic quantum entanglement; F. Fillaux. Probing short-lived entanglement with inelastic X-ray scattering; H. Nauman et al. Proton-proton correlations in condensed matter; E. B. Karlsson. Is Fermi’s golden rule always true for Compton scattering?; I. E. Mazet et al. On correlation approach to scattering in the decoherence timescale; C. A. Chatzidimitriou-Dreismann and S. Stenholm. Part VII Coherence and entanglement in mesoscopic systems. Coherence and entanglement in mesoscopic systems; M. Blaauboer et al. Probe scattering by fluctuating multiatom ensembles in optical lattices; M. Blaauboer et al. Bose-Einstein condensates with laser-induced dipole-dipole interactions; D. O’Dell et al.Atom optics with Bose-Einstein condensation using optical potentials; N. Katz et al. A mesoscopic Mach-Zehnder interferometer; Y. Ji et al. Coherent transport by adiabatic pumping; M. Blaauboer. Zeno and anti-Zeno effects in driven josephson junctions; A. Barone et al. Fabrication of 'quiet' superconducting flux-qubits; E. Sarnelli et al.Broken symmetry and coherence; A. M. Dykhne and A. G. Rudavets. References , Index