# Browsing by Subject "Open quantum systems"

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Item Connecting asymmetric time evolution to the dynamical irreversibility of open quantum systems(2012-08) Bryant, Peter William; Böhm, Arno, 1936-; Dicus, Duane; Odell, Edward; Reichl, Linda; Sitz, GregShow more One consequence of a quantum theory in which resonances are mathematically unified with decaying states is an asymmetry in time evolution, even for closed quantum mechanical systems. This time asymmetry is different from the environmentally induced, dynamical irreversibility that is experienced only by open quantum systems and that is quantified by an increase in entropy. To investigate the connection between time asymmetry and dynamical irreversibility, we study open systems within a time asymmetric theory. We find that, when using a time asymmetric theory for open systems, one must relax the assumption that measurements are perfectly repeatable. To treat this problem, we develop a framework in which one can incorporate the interference from multiple environmental systems affecting a single experiment. We also study a kinematic effect of indistinguishability that affects only open systems, and we show how it leads to a monotonic increase in entropy without requiring an active measurement. Finally, within our framework we develop two models that reproduce for open systems the expected and observed phenomena. One is a model of photons scattering inefficiently from a beam splitter. The other is a model of systems undergoing Rabi oscillations and suffering environmental interference. We find that the kinematic effect of indistinguishability can explain for such systems the generally measured Excitation Induced Dephasing, which has previously been treated dynamically.Show more Item Relaxation in harmonic oscillator systems and wave propagation in negative index materials(2009-05) Chimonidou, Antonia; Sudarshan, E. C. G.Show more This dissertation is divided up into two parts, each examining a distinct theme. The rst part of our work concerns itself with open quantum systems and the relaxation phenomena arising from the repeated application of an interaction Hamiltonian on systems composed of quantum harmonic oscillators. For the second part of our work, we shift gears and investigate the wave propagation in left-handed media, or materials with simultaneously negative electric permeability and magnetic permeability . Each of these two parts is complete within its own context. In the rst part of this dissertation, we introduce a relaxation-generating model which we use to study the process by which quantum correlations are created when an interaction Hamiltonian is repeatedly applied to bipartite harmonic oscillator systems for some characteristic time interval . The two important time scales which enter our results are discussed in detail. We show that the relaxation time obtained by the application of this repeated interaction scheme is proportional to both the strength of interaction and to the characteristic time interval . Through discussing the implications of our model, we show that, for the case where the oscillator frequencies are equal, the initial Maxwell-Boltzmann distributions of the uncoupled parts evolve to a new Maxwell-Boltzmann distribution through a series of transient Maxwell-Boltzmann distributions, or quasi-stationary, non-equilibrium states. We further analyze the case in which the two oscillator frequencies are unequal and show how the application of the same model leads to a non-thermal steady state. The calculations are exact and the results are obtained through an iterative process, without using perturbation theory. In the second part of this dissertation, we examine the response of a plane wave incident on a at surface of a left-handed material, a medium characterized by simultaneously negative electric permittivity and magnetic permeability . We do this by solving Maxwell's equations explicitly. In the literature up to date, it has been assumed that negative refractive materials are necessarily frequency dispersive. We propose an alternative to this assumption by suggesting that the requirement of positive energy density can be relaxed, and discuss the implications of such a proposal. More speci cally, we show that once negative energy solutions are accepted, the requirement for frequency dispersion is no longer needed. We further argue that, for the purposes of discussing left-handed materials, the use of group velocity as the physically signi cant quantity is misleading, and suggest that any discussion involving it should be carefully reconsidered.Show more