Resonance scattering and singularities of the scattering function

Recent studies of transport phenomena with complex potentials are explained by generic square root singularities of spectrum and eigenfunctions of non-Hermitian Hamiltonians. Using a two channel problem we demonstrate that such singularities produce a significant effect upon the pole behaviour of the scattering matrix, and more significantly upon the associated residues. This mechanism explains why by proper choice of the system parameters the resonance cross section is increased drastically in one channel and suppressed in the other channel.Comment: 4 pages, 3 figure

Quantum computation in a Ising spin chain taking into account second neighbor couplings

We consider the realization of a quantum computer in a chain of nuclear spins coupled by an Ising interaction. Quantum algorithms can be performed with the help of appropriate radio-frequency pulses. In addition to the standard nearest-neighbor Ising coupling, we also allow for a second neighbor coupling. It is shown, how to apply the 2\pi k method in this more general setting, where the additional coupling eventually allows to save a few pulses. We illustrate our results with two numerical simulations: the Shor prime factorization of the number 4 and the teleportation of a qubit along a chain of 3 qubits. In both cases, the optimal Rabi frequency (to suppress non-resonant effects) depends primarily on the strength of the second neighbor interaction.Comment: 19 pages, 6 figure

Transition from isolated to overlapping resonances in the open system of interacting fermions

AbstractWe study the statistical properties of resonance widths and spacings in an open system of interacting fermions. At the transition between isolated and overlapping resonances, a radical change in the width distribution occurs with segregation of broad (“super-radiant”) and narrow (“trapped”) states. Our main interest is to reveal how this transition is influenced by the onset of chaos in the internal dynamics regulated by the strength of random two-body interaction. In the transitional region, the width distribution and its variance, as well as the distribution of spacings between resonances are strongly affected by internal chaos. The results may be applied to the analysis of neutron cross sections, as well as in the physics of mesoscopic devices with strongly interacting electrons

Quantum Biological Switch Based on Superradiance Transitions

A linear chain of connected sites with two asymmetric sinks, one attached to each end, is used as a simple model of quantum (excitonic and/or electron) transport in photosynthetic biocomplexes. For a symmetric initial population in the middle of the chain, it is expected that transport is mainly directed toward the strongly coupled sink. However, we show that quantum effects radically change this intuitive “classical” mechanism so that transport can occur through the weakly coupled sink with maximal efficiency. Using this capability, we show how to design a quantum switch that can transfer energy or charge to the strongly or weakly coupled branch of the chain, by changing the coupling to the sinks. The operational principles of this quantum device can be understood in terms of superradiance transitions and subradiant states. This switching, being a pure quantum effect, can be used as a witness of wavelike behavior in molecular chains. When realistic data are used for the photosystem II reaction center, this quantum biological switch is shown to retain its reliability, even at room temperature

Quantum Biological Switch Based on Superradiance Transitions

A linear chain of connected sites with two asymmetric sinks, one attached to each end, is used as a simple model of quantum (excitonic and/or electron) transport in photosynthetic bio-c omplexes. For a symmetric initial population in the middle of the chain, it is expected that transport is mainly directed towards the strongly coupled sink. However, we show that quantum effects radically change this intuitive ``classical'' mechanism, so that transport can occur through the weakly coupled sink with maximal efficiency. Using this capability, we show how to design a quantum switch that can transfer energy or charge to the strongly or weakly coupled branch of the chain, by changing the coupling to the sinks. The operational principles of this quantum device can be understood in terms of superradiance tra nsitions and subradiant states. This switching, being a pure quantum effect, can be used as a witness of wave--like behaviour in molecular chains. When realistic data are used for the photosystem II reaction center, this quantum biological switch is shown to retain its reliability, even at room temperature.A linear chain of connected sites with two asymmetric sinks, one attached to each end, is used as a simple model of quantum (excitonic and/or electron) transport in photosynthetic biocomplexes. For a symmetric initial population in the middle of the chain, it is expected that transport is mainly directed toward the strongly coupled sink. However, we show that quantum effects radically change this intuitive "classical" mechanism so that transport can occur through the weakly coupled sink with maximal efficiency. Using this capability, we show how to design a quantum switch that can transfer energy or charge to the strongly or weakly coupled branch of the chain, by changing the coupling to the sinks. The operational principles of this quantum device can be understood in terms of superradiance transitions and subradiant states. This switching, being a pure quantum effect, can be used as a witness of wavelike behavior in molecular chains. When realistic data are used for the photosystem II reaction center, this quantum biological switch is shown to retain its reliability, even at room temperature