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.

Comprehensive collection of papers on entanglement, decoherence and information protection in quantum systems

Editorial Article.- Role of Entanglement in Quantum Computing and Information Processing.- Quantum Ensembles and Quantum Informatics.- Entanglement in Quantum Information Processing.- Easy Control Over Fermionic Computations.- Multiatom and Multiphoton Entanglement.- Multiatom and Multiphoton Entanglement.- On the Advanced Wave Model of Parametric Down-Conversion.- Quantum Logics Based on Four-Photon Entanglement.- Towards Quantum Control of Light: Shaping Quantum Pulses of Light via Coherent Atomic Memory.- Deterministic Entanglement of Single Photons via Coherently Driven Atoms.- Selective Control of High-Order Atomic Coherences.- Strong Entanglement of Bright Light Beams in Controlled Quantum Systems.- Adiabatic and Nonadiabatic Protection from Decoherence.- Adiabatic and Nonadiabatic Protection from Decoherence.- Coherence Protection by the Quantum Zeno Effect.- Possible Implementation of Topologically Protected Qubits by a Novel Class of Josephson Junction Arrays.- Coherence Protection Near Energy Gaps.- Zeno and Anti-Zeno Dynamics.- Non-Markovian Decay and Decoherence in Open Quantum Systems.- Non-Markovian Decay and Decoherence in Open Quantum Systems.- The Varieties of Master Equations.- Quantum Dynamics Effected by Repeated Measurements.- Non-Exponential Motional Damping of Impurity Atoms in Bose-Einstein Condensates.- Internal-Translational Entanglement and Interference in Atoms and Molecules.- Internal-Translational Entanglement and Interference in Atoms and Molecules.- Atom-Mesoscopic Field Entanglement.- Coherence and Decoherence Experiments with Fullerenes.- Distant Entanglement of Macroscopic Gas Samples.- Position and Momentum Entanglement of Dipole-Dipole Interacting Atoms in Optical Lattices.- Investigation of Autler-Townes Effect in Sodium Dimers.- Transition Steering via Space-Dependent Coupling.- Coherence and Decoherence in Rydberg Gases.- Proton Entanglement and Decoherence in Solids.- Schrödinger's Cat States of Protons in Condensed Matter.- Anomalous Neutron Inelastic Cross Sections at eV Energy Transfers.- Quantum Entanglement and Decoherence Due to Coupling of Protons to Electronic Environment.- Attosecond Effects in Scattering of Neutrons and Electrons from Protons.- Macroscopic Quantum Entanglement in the KHCO3 Crystal.- Probing Short-Lived Entanglement with Inelastic X-ray Scattering.- Proton-Proton Correlations in Condensed Matter.- Is Fermi's Golden Rule Always True for Compton Scattering?.- On Correlation Approach to Scattering in the Decoherence Timescale.- Coherence and Entanglement in Mesoscopic Systems.- Coherence and Entanglement in Mesoscopic Systems.- Probe Scattering by Fluctuating Multi-Atom Ensembles in Optical Lattices.- Bose-Einstein Condensates with Laser-Induced Dipole-Dipole Interactions.- Atom Optics with Bose-Einstein Condensation Using Optical Potentials.- A Mesoscopic Mach-Zehnder Interferometer.- Coherent Transport by Adiabatic Pumping.- Zeno and Anti-Zeno Effects in Driven Josephson Junctions: Control of Macroscopic Quantum Tunneling.- Employment of Submicron YBA2CU3O7-x Grain Boundary Junctions for the Fabrication of " Quiet" Superconducting Flux-Qubits.- Broken Symmetry and Coherence of Molecular Vibrations in Tunnel Transitions.