9 research outputs found
Survival probability of surface excitations in a 2d lattice: non-Markovian effects and Survival Collapse
The evolution of a surface excitation in a two dimentional model is analyzed.
I) It starts quadratically up to a spreading time t_{S}. II) It follows an
exponential behavior governed by a self-consistent Fermi Golden Rule. III) At
longer times, the exponential is overrun by an inverse power law describing
return processes governed by quantum diffusion. At this last transition time
t_{R} a survival collapse becomes possible, bringing the survival probability
down by several orders of magnitude. We identify this strongly destructive
interference as an antiresonance in the time domain.Comment: 4 pages, 3 figures. Braz. Journ. of Phys., in press. Braz. Journ. of
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Braz. Journ. of Phys., in pres
Survival Probability of a Local Excitation in a Non-Markovian Environment: Survival Collapse, Zeno and Anti-Zeno effects
The decay dynamics of a local excitation interacting with a non-Markovian
environment, modeled by a semi-infinite tight-binding chain, is exactly
evaluated. We identify distinctive regimes for the dynamics. Sequentially: (i)
early quadratic decay of the initial-state survival probability, up to a
spreading time , (ii) exponential decay described by a self-consistent
Fermi Golden Rule, and (iii) asymptotic behavior governed by quantum diffusion
through the return processes and leading to an inverse power law decay. At this
last cross-over time a survival collapse becomes possible. This could
reduce the survival probability by several orders of magnitude. The cross-overs
times and allow to assess the range of applicability of the
Fermi Golden Rule and give the conditions for the observation of the Zeno and
Anti-Zeno effect
Effective one-body dynamics in multiple-quantum NMR experiments
A suitable NMR experiment in a one-dimensional dipolar coupled spin system
allows one to reduce the natural many-body dynamics into effective one-body
dynamics. We verify this in a polycrystalline sample of hydroxyapatite (HAp) by
monitoring the excitation of NMR many-body superposition states: the
multiple-quantum coherences. The observed effective one-dimensionality of HAp
relies on the quasi 1d structure of the dipolar coupled network that, as we
show here, is dynamically enhanced by the quantum Zeno effect. Decoherence is
also probed through a Loschmidt echo experiment, where the time reversal is
implemented on the double-quantum Hamiltonian, I_{i,+}I_{j,+} + I_{i,-}I_{j,-}.
We contrast the decoherence of adamantane, a standard 3d system, with that of
HAp. While the first shows an abrupt Fermi-type decay, HAp presents a smooth
exponential law.Comment: 8 pages, 6 figure
Biobased supramolecular ionic networks with optimized crystallinity and mechanical properties as promising dynamic materials for eutectogels design
Ionic supramolecular networks are attractive materials for technological applications with unique properties such as ionic conductivity, stimuli-responsiveness, recyclability, and self-healing. Herein, new semicrystalline supramolecular ionic networks are designed from fully biobased building blocks such as tartaric acid, phytic acid, sebacic acid, and a fatty dimer diamine (Priamine™ 1071). The combination of tartaric acid with Priamine™ 1071 results in a crystalline and brittle polymer, but its molecular regularity can be controlled by incorporating sebacic acid or phytic acid, affording tough materials with appropriate mechanical properties (elastic moduli ranging 19–42 MPa). Furthermore, the ionic polymers show network-to-liquid phase transitions between 75 and 127 °C, and in the liquid state, they were found to be miscible with a lithium-based deep eutectic solvent, yielding flexible and conductive eutectogels. Altogether, these dynamic networks could open new prospects for developing fully green soft ionic materials from their combination with other innovative and low-cost eutectic mixtures.Open Access funding provided by the University of Basque Country. The financial support received from CONICET and ANPCyT (PICT 2018-01032) (Argentina) is gratefully acknowledged
Non-Markovian decay beyond the Fermi Golden Rule: Survival Collapse of the polarization in spin chains
The decay of a local spin excitation in an inhomogeneous spin chain is
evaluated exactly: I) It starts quadratically up to a spreading time t_{S}. II)
It follows an exponential behavior governed by a self-consistent Fermi Golden
Rule. III) At longer times, the exponential is overrun by an inverse power law
describing return processes governed by quantum diffusion. At this last
transition time t_{R} a survival collapse becomes possible, bringing the
polarization down by several orders of magnitude. We identify this strongly
destructive interference as an antiresonance in the time domain. These general
phenomena are suitable for observation through an NMR experiment.Comment: corrected versio
A Shannon-Tsallis transformation
We determine a general link between two different solutions of the MaxEnt
variational problem, namely, the ones that correspond to using either Shannon's
or Tsallis' entropies in the concomitant variational problem. It is shown that
the two variations lead to equivalent solutions that take different appearances
but contain the same information. These solutions are linked by our
transformation
Optical switching of nuclear spin–spin couplings in semiconductors
Two-qubit operation is an essential part of quantum computation. However, solid-state nuclear magnetic resonance quantum computing has not been able to fully implement this functionality, because it requires a switchable inter-qubit coupling that controls the time evolutions of entanglements. Nuclear dipolar coupling is beneficial in that it is present whenever nuclear–spin qubits are close to each other, while it complicates two-qubit operation because the qubits must remain decoupled to prevent unwanted couplings. Here we introduce optically controllable internuclear coupling in semiconductors. The coupling strength can be adjusted externally through light power and even allows on/off switching. This feature provides a simple way of switching inter-qubit couplings in semiconductor-based quantum computers. In addition, its long reach compared with nuclear dipolar couplings allows a variety of options for arranging qubits, as they need not be next to each other to secure couplings