8,086 research outputs found
Robust Quantum State Transfer in Random Unpolarized Spin Chains
We propose and analyze a new approach for quantum state transfer between
remote spin qubits. Specifically, we demonstrate that coherent quantum coupling
between remote qubits can be achieved via certain classes of random,
unpolarized (infinite temperature) spin chains. Our method is robust to
coupling strength disorder and does not require manipulation or control over
individual spins. In principle, it can be used to attain perfect state transfer
over arbitrarily long range via purely Hamiltonian evolution and may be
particularly applicable in a solid-state quantum information processor. As an
example, we demonstrate that it can be used to attain strong coherent coupling
between Nitrogen-Vacancy centers separated by micrometer distances at room
temperature. Realistic imperfections and decoherence effects are analyzed.Comment: 4 pages, 2 figures. V2: Modified discussion of disorder, added
references - final version as published in Phys. Rev. Let
On the error term in Weyl's law for the Heisenberg manifolds (II)
In this paper we study the mean square of the error term in the Weyl's law of
an irrational -dimensional Heisenberg manifold . An asymptotic formula
is established
Two-dimensional molecular para-hydrogen and ortho-deuterium at zero temperature
We study molecular para-hydrogen (p-) and ortho-deuterium
(o-) in two dimensions and in the limit of zero temperature by
means of the diffusion Monte Carlo method. We report energetic and structural
properties of both systems like the total and kinetic energy per particle,
radial pair distribution function, and Lindemann's ratio in the low pressure
regime. By comparing the total energy per particle as a function of the density
in liquid and solid p-, we show that molecular para-hydrogen, and
also ortho-deuterium, remain solid at zero temperature. Interestingly, we
assess the quality of three different symmetrized trial wave functions, based
on the Nosanow-Jastrow model, in the p- solid film at the
variational level. In particular, we analyze a new type of symmetrized trial
wave function which has been used very recently to describe solid He and
found that also characterizes hydrogen satisfactorily. With this wave function,
we show that the one-body density matrix of solid p- possesses off-diagonal long range order, with a condensate fraction
that increases sizably in the negative pressure regime.Comment: 11 pages, 9 figure
Two-photon interference with two independent pseudo-thermal sources
The nature of two-photon interference is a subject that has aroused renewed
interest in recent years and is still under debate. In this paper we report the
first observation of two-photon interference with independent pseudo-thermal
sources in which sub-wavelength interference is observed. The phenomenon may be
described in terms of the classical statistical distribution of the two sources
and their optical transfer functions.Comment: Phys. Rev. A 74, 053807 (2006
Effective Vortex Pinning in MgB2 thin films
We discuss pinning properties of MgB2 thin films grown by pulsed-laser
deposition (PLD) and by electron-beam (EB) evaporation. Two mechanisms are
identified that contribute most effectively to the pinning of vortices in
randomly oriented films. The EB process produces low defected crystallites with
small grain size providing enhanced pinning at grain boundaries without
degradation of Tc. The PLD process produces films with structural disorder on a
scale less that the coherence length that further improves pinning, but also
depresses Tc
Superconducting magnesium diboride films on Silicon with Tc0 about 24K grown via vacuum annealing from stoichiometric precursors
Superconducting magnesium diboride films with Tc0 ~ 24 K and sharp transition
\~ 1 K were successfully prepared on silicon substrates by pulsed laser
deposition from a stoichiometric MgB2 target. Contrary to previous reports,
anneals at 630 degree and a background of 2x10^(-4) torr Ar/4%H2 were performed
without the requirement of Mg vapor or an Mg cap layer. This integration of
superconducting MgB2 films on silicon may thus prove enabling in
superconductor-semiconductor device applications. Images of surface morphology
and cross-section profiles by scanning electron microscopy (SEM) show that the
films have a uniform surface morphology and thickness. Energy dispersive
spectroscopy (EDS) reveals these films were contaminated with oxygen,
originating either from the growth environment or from sample exposure to air.
The oxygen contamination may account for the low Tc for those in-situ annealed
films, while the use of Si as the substrate does not result in a decrease in Tc
as compared to other substrates.Comment: 5 pages, 4 figures, 15 references; due to file size limit, images
were blure
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