16,329 research outputs found
Quantum information processing via a lossy bus
We describe a method to perform two qubit measurements and logic operations
on pairs of qubits which each interact with a harmonic oscillator degree of
freedom (the \emph{bus}), but do not directly interact with one another. Our
scheme uses only weak interactions between the qubit and the bus, homodyne
measurements, and single qubit operations. In contrast to earlier schemes, the
technique presented here is extremely robust to photon loss in the bus mode,
and can function with high fidelity even when the rate of photon loss is
comparable to the strength of the qubit-bus coupling.Comment: Added more discussion on effects of noise. Typos correcte
Development and evaluation of a device to simulate a sonic boom
A device to simulate the vibrational and acoustical properties of a sonic boom was developed and evaluated. The design employed a moving circular diaphragm which produced pressure variations by altering the volume of an air-tight enclosure that was located adjacent to an acoustical test chamber. A review of construction oriented problems, along with their solutions, is presented. The simulator is shown to produce the effects of sonic booms having pressure signatures with rise times as low as 5 milliseconds, durations as short as 80 milliseconds, and overpressures as high as 2.5 pounds per square foot. Variations in the signatures are possible by independent adjustments of the simulator. The energy spectral density is also shown to be in agreement with theory and with actual measurements for aircraft
Quantum computation via measurements on the low-temperature state of a many-body system
We consider measurement-based quantum computation using the state of a
spin-lattice system in equilibrium with a thermal bath and free to evolve under
its own Hamiltonian. Any single qubit measurements disturb the system from
equilibrium and, with adaptive measurements performed at a finite rate, the
resulting dynamics reduces the fidelity of the computation. We show that it is
possible to describe the loss in fidelity by a single quantum operation on the
encoded quantum state that is independent of the measurement history. To
achieve this simple description, we choose a particular form of spin-boson
coupling to describe the interaction with the environment, and perform
measurements periodically at a natural rate determined by the energy gap of the
system. We found that an optimal cooling exists, which is a trade-off between
keeping the system cool enough that the resource state remains close to the
ground state, but also isolated enough that the cooling does not strongly
interfere with the dynamics of the computation. For a sufficiently low
temperature we obtain a fault-tolerant threshold for the couplings to the
environment.Comment: 9 pages, 3 figures; v2 published versio
Statistical Dynamics of Religions and Adherents
Religiosity is one of the most important sociological aspects of populations.
All religions may evolve in their beliefs and adapt to the society
developments. A religion is a social variable, like a language or wealth, to be
studied like any other organizational parameter.
Several questions can be raised, as considered in this study: e.g. (i) from a
``macroscopic'' point of view : How many religions exist at a given time? (ii)
from a ``microscopic'' view point: How many adherents belong to one religion?
Does the number of adherents increase or not, and how? No need to say that if
quantitative answers and mathematical laws are found, agent based models can be
imagined to describe such non-equilibrium processes.
It is found that empirical laws can be deduced and related to preferential
attachment processes, like on evolving network; we propose two different
algorithmic models reproducing as well the data. Moreover, a population
growth-death equation is shown to be a plausible modeling of evolution dynamics
in a continuous time framework. Differences with language dynamic competition
is emphasized.Comment: submitted to EP
Coupling of spacetime atoms and spin foam renormalisation from group field theory
We study the issue of coupling among 4-simplices in the context of spin foam
models obtained from a group field theory formalism. We construct a
generalisation of the Barrett-Crane model in which an additional coupling
between the normals to tetrahedra, as defined in different 4-simplices that
share them, is present. This is realised through an extension of the usual
field over the group manifold to a five argument one. We define a specific
model in which this coupling is parametrised by an additional real parameter
that allows to tune the degree of locality of the resulting model,
interpolating between the usual Barrett-Crane model and a flat BF-type one.
Moreover, we define a further extension of the group field theory formalism in
which the coupling parameter enters as a new variable of the field, and the
action presents derivative terms that lead to modified classical equations of
motion. Finally, we discuss the issue of renormalisation of spin foam models,
and how the new coupled model can be of help regarding this.Comment: RevTeX, 18 pages, no figure
Spin Foam Models of Yang-Mills Theory Coupled to Gravity
We construct a spin foam model of Yang-Mills theory coupled to gravity by
using a discretized path integral of the BF theory with polynomial interactions
and the Barret-Crane ansatz. In the Euclidian gravity case we obtain a vertex
amplitude which is determined by a vertex operator acting on a simple spin
network function. The Euclidian gravity results can be straightforwardly
extended to the Lorentzian case, so that we propose a Lorentzian spin foam
model of Yang-Mills theory coupled to gravity.Comment: 10 page
Observables in 3-dimensional quantum gravity and topological invariants
In this paper we report some results on the expectation values of a set of
observables introduced for 3-dimensional Riemannian quantum gravity with
positive cosmological constant, that is, observables in the Turaev-Viro model.
Instead of giving a formal description of the observables, we just formulate
the paper by examples. This means that we just show how an idea works with
particular cases and give a way to compute 'expectation values' in general by a
topological procedure.Comment: 24 pages, 47 figure
Radio Astronomy
Contains reports on one research project.National Aeronautics and Space Administration (Grant NGL 22-009-016)National Aeronautics and Space Administration (Grant NGR 22-009-421)National Science Foundation Grant GP-2076
Fractal Weyl law behavior in an open, chaotic Hamiltonian system
We numerically show fractal Weyl law behavior in an open Hamiltonian system
that is described by a smooth potential and which supports numerous
above-barrier resonances. This behavior holds even relatively far away from the
classical limit. The complex resonance wave functions are found to be localized
on the fractal classical repeller.Comment: 4 pages, 3 figures. to appear in Phys Rev
A Storage Ring for Neutral Atoms
We have demonstrated a storage ring for ultra-cold neutral atoms. Atoms with
mean velocities of 1 m/s corresponding to kinetic energies of ~100 neV are
confined to a 2 cm diameter ring by magnetic forces produced by two
current-carrying wires. Up to 10^6 atoms are loaded at a time in the ring, and
7 revolutions are clearly observed. Additionally, we have demonstrated multiple
loading of the ring and deterministic manipulation of the longitudinal velocity
distribution of the atoms using applied laser pulses. Applications of this ring
include large area atom interferometers and cw monochromatic atomic beam
generation.Comment: 4 pages, 5 figure
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