54 research outputs found
Dynamical studies of macroscopic superposition states: Phase engineering of controlled entangled number states of Bose-Einstein condensate in multiple wells
We provide a scheme for the generation of entangled number states of
Bose-Einstein condensates in multiple wells with cyclic pairwise connectivity.
The condensate ground state in a multiple well trap can self-evolve, when phase
engineered with specific initial phase differences between the neighboring
wells, to a macroscopic superposition state with controllable entanglement --
to multiple well generalization of double well NOON states. We demonstrate
through numerical simulations the creation of entangled states in three and
four wells and then explore the creation of "larger" entangled states where
there are either a larger number of particles in each well or a larger number
of wells. The type of entanglement produced as the particle numbers, or
interaction strength, increases changes in a novel and initially unexpected
manner.Comment: 13 pages, 14 figure
Persistent entanglement in two coupled SQUID rings in the quantum to classical transition - A quantum jumps approach
We explore the quantum-classical crossover of two coupled, identical,
superconducting quantum interference device (SQUID) rings. The motivation for
this work is based on a series of recent papers. In ~[1] we showed that the
entanglement characteristics of chaotic and periodic (entrained) solutions of
the Duffing oscillator differed significantly and that in the classical limit
entanglement was preserved only in the chaotic-like solutions. However, Duffing
oscillators are a highly idealised toy system. Motivated by a wish to explore
more experimentally realisable systems we extended our work in [2,3] to an
analysis of SQUID rings. In [3] we showed that the two systems share a common
feature. That is, when the SQUID ring's trajectories appear to follow (semi)
classical orbits entanglement persists. Our analysis in[3] was restricted to
the quantum state diffusion unravelling of the master equation - representing
unit efficiency heterodyne detection (or ambi-quadrature homodyne detection).
Here we show that very similar behaviour occurs using the quantum jumps
unravelling of the master equation. Quantum jumps represents a discontinuous
photon counting measurement process. Hence, the results presented here imply
that such persistent entanglement is independent of measurement process and
that our results may well be quite general in nature.Comment: 6 pages, 3 figures. Published as part of a special issue for the 11th
International Conference on Squeezed States and Uncertainty Relations/4th
Feynman festival in Olomouc 2009 (This paper extends the results presented in
arXiv:0909.4488
From Quantum to Classical: the Quantum State Diffusion Model
Quantum mechanics is nonlocal. Classical mechanics is local. Consequently classical mechanics can not explain all quantum phenomena. Conversely, it is cumbersome to use quantum mechanics to describe classical phenomena. Not only are the computations more complex, but - and this is the main point - it is conceptually more difficult: one has to argue that nonlocality, entanglement and the principle of superposition can be set aside when crossing the "quantum principle of superposition should become irrelevant in the classical limit. But why should one argue? Shouldn't it just come out of the equations? Does it come out of the equations? This contribution is about the last question. And the answer is: "it depends on which equation"
Anatomy of quantum chaotic eigenstates
The eigenfunctions of quantized chaotic systems cannot be described by
explicit formulas, even approximate ones. This survey summarizes (selected)
analytical approaches used to describe these eigenstates, in the semiclassical
limit. The levels of description are macroscopic (one wants to understand the
quantum averages of smooth observables), and microscopic (one wants
informations on maxima of eigenfunctions, "scars" of periodic orbits, structure
of the nodal sets and domains, local correlations), and often focusses on
statistical results. Various models of "random wavefunctions" have been
introduced to understand these statistical properties, with usually good
agreement with the numerical data. We also discuss some specific systems (like
arithmetic ones) which depart from these random models.Comment: Corrected typos, added a few references and updated some result
The Potential Energy Surface in Molecular Quantum Mechanics
The idea of a Potential Energy Surface (PES) forms the basis of almost all
accounts of the mechanisms of chemical reactions, and much of theoretical
molecular spectroscopy. It is assumed that, in principle, the PES can be
calculated by means of clamped-nuclei electronic structure calculations based
upon the Schr\"{o}dinger Coulomb Hamiltonian. This article is devoted to a
discussion of the origin of the idea, its development in the context of the Old
Quantum Theory, and its present status in the quantum mechanics of molecules.
It is argued that its present status must be regarded as uncertain.Comment: 18 pages, Proceedings of QSCP-XVII, Turku, Finland 201
Quantum Spacetime Phenomenology
I review the current status of phenomenological programs inspired by
quantum-spacetime research. I stress in particular the significance of results
establishing that certain data analyses provide sensitivity to effects
introduced genuinely at the Planck scale. And my main focus is on
phenomenological programs that managed to affect the directions taken by
studies of quantum-spacetime theories.Comment: 125 pages, LaTex. This V2 is updated and more detailed than the V1,
particularly for quantum-spacetime phenomenology. The main text of this V2 is
about 25% more than the main text of the V1. Reference list roughly double
- …