scholarly journals Quantum irreversible decoherence behaviour in open quantum systems with few degrees of freedom: Application to 1H NMR reversion experiments in nematic liquid crystals

2013 ◽  
Vol 139 (15) ◽  
pp. 154901 ◽  
Author(s):  
H. H. Segnorile ◽  
R. C. Zamar
Keyword(s):  
Liquid Crystals ◽  
1H Nmr ◽  
Degrees Of Freedom ◽  
Open Quantum Systems ◽  
Nematic Liquid Crystals ◽  
Quantum Systems ◽  
Open Quantum

scholarly journals Quasi-Lie Brackets and the Breaking of Time-Translation Symmetry for Quantum Systems Embedded in Classical Baths

Symmetry ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 518 ◽  
Author(s):  
Alessandro Sergi ◽  
Gabriel Hanna ◽  
Roberto Grimaudo ◽  
Antonino Messina
Keyword(s):  
Constant Temperature ◽  
Degrees Of Freedom ◽  
Open Quantum Systems ◽  
Hamiltonian Dynamics ◽  
Quantum Systems ◽  
Classical Dynamics ◽  
Open Quantum ◽  
Time Translation ◽  
Translation Symmetry ◽  
Lie Brackets

Many open quantum systems encountered in both natural and synthetic situations are embedded in classical-like baths. Often, the bath degrees of freedom may be represented in terms of canonically conjugate coordinates, but in some cases they may require a non-canonical or non-Hamiltonian representation. Herein, we review an approach to the dynamics and statistical mechanics of quantum subsystems embedded in either non-canonical or non-Hamiltonian classical-like baths which is based on operator-valued quasi-probability functions. These functions typically evolve through the action of quasi-Lie brackets and their associated Quantum-Classical Liouville Equations, or through quasi-Lie brackets augmented by dissipative terms. Quasi-Lie brackets possess the unique feature that, while conserving the energy (which the Noether theorem links to time-translation symmetry), they violate the time-translation symmetry of their algebra. This fact can be heuristically understood in terms of the dynamics of the open quantum subsystem. We then describe an example in which a quantum subsystem is embedded in a bath of classical spins, which are described by non-canonical coordinates. In this case, it has been shown that an off-diagonal open-bath geometric phase enters into the propagation of the quantum-classical dynamics. Next, we discuss how non-Hamiltonian dynamics may be employed to generate the constant-temperature evolution of phase space degrees of freedom coupled to the quantum subsystem. Constant-temperature dynamics may be generated by either a classical Langevin stochastic process or a Nosé–Hoover deterministic thermostat. These two approaches are not equivalent but have different advantages and drawbacks. In all cases, the calculation of the operator-valued quasi-probability function allows one to compute time-dependent statistical averages of observables. This may be accomplished in practice using a hybrid Molecular Dynamics/Monte Carlo algorithms, which we outline herein.

scholarly journals Accurate Truncations of Chain Mapping Models for Open Quantum Systems

Nanomaterials ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 2104
Author(s):  
Mónica Sánchez-Barquilla ◽  
Johannes Feist
Keyword(s):  
Degrees Of Freedom ◽  
Nearest Neighbor ◽  
Open Quantum Systems ◽  
Quantum Systems ◽  
Open Quantum ◽  
Research Fields ◽  
A Chain ◽  
Chain Lengths ◽  
Mapping Models ◽  
Nearest Neighbor Coupling

The dynamics of open quantum systems are of great interest in many research fields, such as for the interaction of a quantum emitter with the electromagnetic modes of a nanophotonic structure. A powerful approach for treating such setups in the non-Markovian limit is given by the chain mapping where an arbitrary environment can be transformed to a chain of modes with only nearest-neighbor coupling. However, when long propagation times are desired, the required long chain lengths limit the utility of this approach. We study various approaches for truncating the chains at manageable lengths while still preserving an accurate description of the dynamics. We achieve this by introducing losses to the chain modes in such a way that the effective environment acting on the system remains unchanged, using a number of different strategies. Furthermore, we demonstrate that extending the chain mapping to allow next-nearest neighbor coupling permits the reproduction of an arbitrary environment, and adding longer-range interactions does not further increase the effective number of degrees of freedom in the environment.

scholarly journals Reduced Operator Approximation for Modelling Open Quantum Systems

2015 ◽  
Vol 22 (02) ◽  
pp. 1550008
Author(s):  
A. Werpachowska
Keyword(s):  
Quantum Dynamics ◽  
Quantum Coherence ◽  
Degrees Of Freedom ◽  
Open Quantum Systems ◽  
Interaction Strength ◽  
Quantum Systems ◽  
Computationally Efficient ◽  
Memory Length ◽  
Open Quantum ◽  
Operator Approximation

We present the reduced operator approximation: a simple, physically transparent and computationally efficient method of modelling open quantum systems. It employs the Heisenberg picture of the quantum dynamics, which allows us to focus on the system degrees of freedom in a natural and easy way. We describe different variants of the method, low- and high-order in the system–bath interaction operators, defining them for either general quantum harmonic oscillator baths or specialising them for independent baths with Lorentzian spectral densities. Its wide applicability is demonstrated on the examples of systems coupled to different baths (with varying system–bath interaction strength and bath memory length), and compared with the exact pseudomode and the popular quantum state diffusion approach. The method captures the decoherence of the system interacting with the bath, while conserving the total energy. Our results suggest that quantum coherence effects persist in open quantum systems for much longer times than previously thought.

DECOHERENCE INDUCED TRANSITION FROM QUANTUM TO CLASSICAL DYNAMICS

2003 ◽  
Vol 15 (03) ◽  
pp. 217-243 ◽  
Author(s):  
PH. BLANCHARD ◽  
R. OLKIEWICZ
Keyword(s):  
Dynamical Systems ◽  
Infinite Number ◽  
Degrees Of Freedom ◽  
Open Quantum Systems ◽  
Quantum Systems ◽  
Classical Dynamics ◽  
Open Quantum ◽  
Classical Behavior

Framework for a general discussion of environmentally induced classical properties, like superselection rules, privileged basis and classical behavior, in quantum systems with both finite and infinite number of degrees of freedom is proposed. A number of examples showing that classical properties do not have to be postulated as an independent ingredient are given. In particular, it is shown that infinite open quantum systems in some cases may behave like simple classical dynamical systems.

Dynamics of Open Quantum Systems Using Parametric Representation with Coherent States

2013 ◽  
Vol 20 (03) ◽  
pp. 1340002 ◽  
Author(s):  
Dario Calvani ◽  
Alessandro Cuccoli ◽  
Nikitas I. Gidopoulos ◽  
Paola Verrucchi
Keyword(s):  
Coherent States ◽  
Degrees Of Freedom ◽  
Irreversible Process ◽  
Open Quantum Systems ◽  
Parametric Representation ◽  
Quantum Systems ◽  
Entanglement Generation ◽  
Open Quantum ◽  
Alternative Description ◽  
Reduced Density

Open quantum systems and their dynamics are usually studied in terms of reduced density matrices. This approach allows a nonsymmetric description, which is useful when one of the two subsystems is to be considered an environment, at the expense of a loss of information, as tracing out the environmental degrees of freedom is an irreversible process. This has a series of consequences which can be severe. In this work we present an alternative description, which is still nonsymmetric but yet exact: It is based on a parametric representation of composite systems, as obtained by introducing environmental coherent states, such that the principal system get to be described by a set of pure states parametrically dependent on environmental variables. The representation allows one to relate properties which typically arise in studying systems with parametrically dependent Hamiltonians, such as the emergence of geometrical phases, with features which specifically characterize open quantum systems, such as decoherence and entanglement generation.

scholarly journals An Operator-Based Exact Treatment of Open Quantum Systems

2005 ◽  
Vol 12 (02) ◽  
pp. 163-177 ◽  
Author(s):  
S. Nicolosi
Keyword(s):  
Open System ◽  
Degrees Of Freedom ◽  
Quantum Physics ◽  
Open Systems ◽  
Open Quantum Systems ◽  
Quantum Systems ◽  
Open Quantum ◽  
Environment Model ◽  
Probabilistic Description ◽  
Deterministic Processes

Quantum mechanics must be regarded as open systems. On one hand, this is due to the fact that, like in classical physics, any realistic system is subjected to a coupling to an uncontrollable environment which influences it in a non-negligible way. The theory of open quantum systems thus plays a major role in many applications of quantum physics since perfect isolation of quantum system is not possible and since a complete microscopic description or control of the environment degrees of freedom is not feasible or only partially so [1]. Practical considerations therefore force one to seek for a simpler, effectively probabilistic description in terms of an open system. There is a close physical and mathematical connection between the evolution of an open system, the state changes induced by quantum measurements, and the classical notion of a stochastic process. The paper provides a bibliographic review of this interrelations, it shows the mathematical equivalence between markovian master equation and generalized piecewise deterministic processes [1] and it introduces the open system in an open observed environment model.

Relaxation of interacting open quantum systems

2018 ◽  
Vol 189 (05) ◽  
Author(s):  
Vladislav Yu. Shishkov ◽  
Evgenii S. Andrianov ◽  
Aleksandr A. Pukhov ◽  
Aleksei P. Vinogradov ◽  
A.A. Lisyansky
Keyword(s):  
Open Quantum Systems ◽  
Quantum Systems ◽  
Open Quantum
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