3,417 research outputs found
Surface location of sodium atoms attached to He-3 nanodroplets
We have experimentally studied the electronic excitation of
Na atoms attached to He droplets by means of laser-induced fluorescence as
well as beam depletion spectroscopy. From the similarities of the spectra
(width/shift of absorption lines) with these of Na on He droplets, we
conclude that sodium atoms reside in a ``dimple'' on the droplet surface. The
experimental results are supported by Density Functional calculations at zero
temperature, which confirm the surface location of sodium on He droplets,
and provide a microscopic description of the ``dimple'' structure.Comment: 4 pages, 5 figure
Dynamics of a superconducting qubit coupled to the quantized cavity field: a unitary transformation approach
We present a novel approach for studying the dynamics of a superconducting
qubit in a cavity. We succeed in linearizing the Hamiltonian through the
application of an appropriate unitary transformation followed by a rotating
wave approximation (RWA). For certain values of the parameters involved, we
show that it is possible to obtain a a Jaynes-Cummings type Hamiltonian. As an
example, we show the existence of super-revivals for the qubit inversion
Study of losses during Continuous Transfer Extraction at CERN Proton Synchrotron
The proton beams used for the fixed target physics at the SPS are extracted from the PS at 14 GeV/c in five turns, using a technique called Continuous Transfer (CT). During this extraction, large losses are observed in straight sections were the machine aperture should be large enough to accommodate the circulating beam without any loss. These losses are due to particles scattered by the electrostatic septum used to slice the beam and defocused by a quadrupole used during the extraction. Simulations and experimental results are presented
Field Purification in the intensity-dependent Jaynes-Cummings model
We have found that, in the intensity-dependent Jaynes-Cummings model, a field
initially prepared in a statistical mixture of two coherent states,
and , evolves toward a pure state. We have also shown that an
even-coherent state turns periodically a into rotated odd-coherent state during
the evolution.Comment: 14 pages, RevTex, 3 figures, accepted for publication in Physics
Letters
Beam losses in the PS during CT extraction
The proton beams used for the fixed target physics at the SPS are extracted from the PS at 14 GeV/c in five turns, using a technique called Continuous Transfer (CT). During this extraction, large losses are observed in straight sections were the machine aperture should be large enough to accommodate the circulating beam without any loss. These losses are due to particles scattered by the electrostatic septum used to slice the beam and defocused by a quadrupole used during the extraction. Simulations and experimental results are presented
Zombie Vortex Instability. II. Thresholds to Trigger Instability and the Properties of Zombie Turbulence in the Dead Zones of Protoplanetary Disks
In Zombie Vortex Instability (ZVI), perturbations excite critical layers in
stratified, rotating shear flow (as in protoplanetary disks), causing them to
generate vortex layers, which roll-up into anticyclonic zombie vortices and
cyclonic vortex sheets. The process is self-sustaining as zombie vortices
perturb new critical layers, spawning a next generation of zombie vortices.
Here, we focus on two issues: the minimum threshold of perturbations that
trigger self-sustaining vortex generation, and the properties of the late-time
zombie turbulence on large and small scales. The critical parameter that
determines whether ZVI is triggered is the magnitude of the vorticity on the
small scales (and not velocity), the minimum Rossby number needed for
instability is for , where is
the Brunt-V\"ais\"al\"a frequency. While the threshold is set by vorticity, it
is useful to infer a criterion on the Mach number, for Kolmogorov noise, the
critical Mach number scales with Reynolds number: . In protoplanetary disks, this is .
On large scales, zombie turbulence is characterized by anticyclones and
cyclonic sheets with typical Rossby number 0.3. The spacing of the
cyclonic sheets and anticyclones appears to have a "memory" of the spacing of
the critical layers. On the small scales, zombie turbulence has no memory of
the initial conditions and has a Kolmogorov-like energy spectrum. While our
earlier work was in the limit of uniform stratification, we have demonstrated
that ZVI works for non-uniform Brunt-V\"ais\"al\"a frequency profiles that may
be found in protoplanetary disks.Comment: Submitted to Ap
Finite size effects in adsorption of helium mixtures by alkali substrates
We investigate the behavior of mixed 3He-4He droplets on alkali surfaces at
zero temperature, within the frame of Finite Range Density Functional theory.
The properties of one single 3He atom on 4He_N4 droplets on different alkali
surfaces are addressed, and the energetics and structure of 4He_N4+3He_N3
systems on Cs surfaces, for nanoscopic 4He drops, are analyzed through the
solutions of the mean field equations for varying number N3 of 3He atoms. We
discuss the size effects on the single particle spectrum of 3He atoms and on
the shapes of both helium distributions.Comment: 12 pages, and 12 figures (PNG format
Quantum Key Distribution using Continuous-variable non-Gaussian States
In this work we present a quantum key distribution protocol using
continuous-variable non-Gaussian states, homodyne detection and post-selection.
The employed signal states are the Photon Added then Subtracted Coherent States
(PASCS) in which one photon is added and subsequently one photon is subtracted.
We analyze the performance of our protocol, compared to a coherent state based
protocol, for two different attacks that could be carried out by the
eavesdropper (Eve). We calculate the secret key rate transmission in a lossy
line for a superior channel (beam-splitter) attack, and we show that we may
increase the secret key generation rate by using the non-Gaussian PASCS rather
than coherent states. We also consider the simultaneous quadrature measurement
(intercept-resend) attack and we show that the efficiency of Eve's attack is
substantially reduced if PASCS are used as signal states.Comment: We have included an analysis of the simultaneous quadrature
measurement attack plus 2 figures; we have also clarified some point
Quantum state engineering via unitary transformations
We construct a Hamiltonian for the generation of arbitrary pure states of the
quantized electromagnetic field. The proposition is based upon the fact that a
unitary transformation for the generation of number states has been already
found. The general unitary transformation here obtained, would allow the use of
nonlinear interactions for the production of pure states. We discuss the
applicability of this method by giving examples of generation of simple
superposition states. We also compare our Hamiltonian with the one resulting
from the interaction of trapped ions with two laser fields.Comment: 5 pages in RevTeX, no figures, accepted for publication in Phys. Rev.
Commutative -algebras of Toeplitz operators on complex projective spaces
We prove the existence of commutative -algebras of Toeplitz operators on
every weighted Bergman space over the complex projective space
. The symbols that define our algebras are those that
depend only on the radial part of the homogeneous coordinates. The algebras
presented have an associated pair of Lagrangian foliations with distinguished
geometric properties and are closely related to the geometry of
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