2,263 research outputs found
A microscopic derivation of the quantum mechanical formal scattering cross section
We prove that the empirical distribution of crossings of a "detector''
surface by scattered particles converges in appropriate limits to the
scattering cross section computed by stationary scattering theory. Our result,
which is based on Bohmian mechanics and the flux-across-surfaces theorem, is
the first derivation of the cross section starting from first microscopic
principles.Comment: 28 pages, v2: Typos corrected, layout improved, v3: Typos corrected.
Accepted for publication in Comm. Math. Phy
Atom-molecule Rabi oscillations in a Mott insulator
We observe large-amplitude Rabi oscillations between an atomic and a
molecular state near a Feshbach resonance. The experiment uses 87Rb in an
optical lattice and a Feshbach resonance near 414 G. The frequency and
amplitude of the oscillations depend on magnetic field in a way that is well
described by a two-level model. The observed density dependence of the
oscillation frequency agrees with the theoretical expectation. We confirmed
that the state produced after a half-cycle contains exactly one molecule at
each lattice site. In addition, we show that for energies in a gap of the
lattice band structure, the molecules cannot dissociate
Pilot Wave model that includes creation and annihilation of particles
The purpose of this paper is to come up with a Pilot Wave model of quantum
field theory that incorporates particle creation and annihilation without
sacrificing determinism. This has been previously attempted in an article by
the same author titled "Incorporating particle creation and annihilation in
Pilot Wave model", in a much less satisfactory way. In this paper I would like
to "clean up" some of the things. In particular, I would like to get rid of a
very unnatural concept of "visibility" of particles, which makes the model much
simpler. On the other hand, I would like to add a mechanism for decoherence,
which was absent in the previous version.Comment: 9 pages, no figure
On the exit statistics theorem of many particle quantum scattering
We review the foundations of the scattering formalism for one particle
potential scattering and discuss the generalization to the simplest case of
many non interacting particles. We point out that the "straight path motion" of
the particles, which is achieved in the scattering regime, is at the heart of
the crossing statistics of surfaces, which should be thought of as detector
surfaces. We sketch a proof of the relevant version of the many particle flux
across surfaces theorem and discuss what needs to be proven for the foundations
of scattering theory in this context.Comment: 15 pages, 4 figures; to appear in the proceedings of the conference
"Multiscale methods in Quantum Mechanics", Accademia dei Lincei, Rome,
December 16-20, 200
Combination of a magnetic Feshbach resonance and an optical bound-to-bound transition
We use laser light near resonant with an optical bound-to-bound transition to
shift the magnetic field at which a Feshbach resonance occurs. We operate in a
regime of large detuning and large laser intensity. This reduces the
light-induced atom-loss rate by one order of magnitude compared to our previous
experiments [D.M. Bauer et al. Nature Phys. 5, 339 (2009)]. The experiments are
performed in an optical lattice and include high-resolution spectroscopy of
excited molecular states, reported here. In addition, we give a detailed
account of a theoretical model that describes our experimental data
Femtosecond x-ray absorption spectroscopy of spin and orbital angular momentum in photoexcited Ni films during ultrafast demagnetization
We follow for the first time the evolution of the spin and orbital angular
momentum of a thin Ni film during ultrafast demagnetization, by means of x-ray
magnetic circular dichroism. Both components decrease with a 130 +/- 40 fs time
constant upon excitation with a femtosecond laser pulse. Additional x-ray
absorption measurements reveal an increase in the spin-orbit interaction by 6
+/- 2 % during this process. This is the experimental demonstration quantifying
the importance of spin-orbit mediated processes during the demagnetization
Improving Quantum Query Complexity of Boolean Matrix Multiplication Using Graph Collision
The quantum query complexity of Boolean matrix multiplication is typically
studied as a function of the matrix dimension, n, as well as the number of 1s
in the output, \ell. We prove an upper bound of O (n\sqrt{\ell}) for all values
of \ell. This is an improvement over previous algorithms for all values of
\ell. On the other hand, we show that for any \eps < 1 and any \ell <= \eps
n^2, there is an \Omega(n\sqrt{\ell}) lower bound for this problem, showing
that our algorithm is essentially tight.
We first reduce Boolean matrix multiplication to several instances of graph
collision. We then provide an algorithm that takes advantage of the fact that
the underlying graph in all of our instances is very dense to find all graph
collisions efficiently
Hypersurface Bohm-Dirac models
We define a class of Lorentz invariant Bohmian quantum models for N entangled
but noninteracting Dirac particles. Lorentz invariance is achieved for these
models through the incorporation of an additional dynamical space-time
structure provided by a foliation of space-time. These models can be regarded
as the extension of Bohm's model for N Dirac particles, corresponding to the
foliation into the equal-time hyperplanes for a distinguished Lorentz frame, to
more general foliations. As with Bohm's model, there exists for these models an
equivariant measure on the leaves of the foliation. This makes possible a
simple statistical analysis of position correlations analogous to the
equilibrium analysis for (the nonrelativistic) Bohmian mechanics.Comment: 17 pages, 3 figures, RevTex. Completely revised versio
A Mott-like State of Molecules
We prepare a quantum state where each site of an optical lattice is occupied
by exactly one molecule. This is the same quantum state as in a Mott insulator
of molecules in the limit of negligible tunneling. Unlike previous Mott
insulators, our system consists of molecules which can collide inelastically.
In the absence of the optical lattice these collisions would lead to fast loss
of the molecules from the sample. To prepare the state, we start from a Mott
insulator of atomic 87Rb with a central region, where each lattice site is
occupied by exactly two atoms. We then associate molecules using a Feshbach
resonance. Remaining atoms can be removed using blast light. Our method does
not rely on the molecule-molecule interaction properties and is therefore
applicable to many systems.Comment: Proceedings of the 20th International Conference on Atomic Physics
(ICAP 2006), edited by C. Roos, H. Haffner, and R. Blatt, AIP Conference
Proceedings, Melville, 2006, Vol. 869, pp. 278-28
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