83 research outputs found
Characterization of meloidogyne species from irrigated rice in southern Brazil.
Edição dos Proceedings do 6th International Congress of Nematology, Cape Town, South Africa, May 2014
Emulating Solid-State Physics with a Hybrid System of Ultracold Ions and Atoms
We propose and theoretically investigate a hybrid system composed of a
crystal of trapped ions coupled to a cloud of ultracold fermions. The ions form
a periodic lattice and induce a band structure in the atoms. This system
combines the advantages of scalability and tunability of ultracold atomic
systems with the high fidelity operations and detection offered by trapped ion
systems. It also features close analogies to natural solid-state systems, as
the atomic degrees of freedom couple to phonons of the ion lattice, thereby
emulating a solid-state system. Starting from the microscopic many-body
Hamiltonian, we derive the low energy Hamiltonian including the atomic band
structure and give an expression for the atom-phonon coupling. We discuss
possible experimental implementations such as a Peierls-like transition into a
period-doubled dimerized state.Comment: 5 pages + appendi
Turbulent jet through porous obstructions under Coriolis effect: an experimental investigation
The present study has the main purpose to experimentally investigate a turbulent momentum jet issued in a basin affected by rotation and in presence of porous obstructions. The experiments were carried out at the Coriolis Platform at LEGI Grenoble (FR). A large and unique set of velocity data was obtained by means of a Particle Image Velocimetry measurement technique while varying the rotation rate of the tank and the density of the canopy. The main differences in jet behavior in various flow configurations were assessed in terms of mean flow, turbulent kinetic energy and jet spreading. The jet trajectory was also detected. The results prove that obstructions with increasing density and increased rotation rates induce a more rapid abatement of both jet velocity and turbulent kinetic energy. The jet trajectories can be scaled by a characteristic length, which is found to be a function of the jet initial momentum, the rotation rate, and the drag exerted by the obstacles. An empirical expression for the latter is also proposed and validated
Interaction-based quantum metrology showing scaling beyond the Heisenberg limit
Quantum metrology studies the use of entanglement and other quantum resources
to improve precision measurement. An interferometer using N independent
particles to measure a parameter X can achieve at best the "standard quantum
limit" (SQL) of sensitivity {\delta}X \propto N^{-1/2}. The same interferometer
using N entangled particles can achieve in principle the "Heisenberg limit"
{\delta}X \propto N^{-1}, using exotic states. Recent theoretical work argues
that interactions among particles may be a valuable resource for quantum
metrology, allowing scaling beyond the Heisenberg limit. Specifically, a
k-particle interaction will produce sensitivity {\delta}X \propto N^{-k} with
appropriate entangled states and {\delta}X \propto N^{-(k-1/2)} even without
entanglement. Here we demonstrate this "super-Heisenberg" scaling in a
nonlinear, non-destructive measurement of the magnetisation of an atomic
ensemble. We use fast optical nonlinearities to generate a pairwise
photon-photon interaction (k = 2) while preserving quantum-noise-limited
performance, to produce {\delta}X \propto N^{-3/2}. We observe super-Heisenberg
scaling over two orders of magnitude in N, limited at large N by higher-order
nonlinear effects, in good agreement with theory. For a measurement of limited
duration, super-Heisenberg scaling allows the nonlinear measurement to overtake
in sensitivity a comparable linear measurement with the same number of photons.
In other scenarios, however, higher-order nonlinearities prevent this crossover
from occurring, reflecting the subtle relationship of scaling to sensitivity in
nonlinear systems. This work shows that inter-particle interactions can improve
sensitivity in a quantum-limited measurement, and introduces a fundamentally
new resource for quantum metrology
Dynamical programming of continuously observed quantum systems
We develop dynamical programming methods for the purpose of optimal control
of quantum states with convex constraints and concave cost and bequest
functions of the quantum state. We consider both open loop and feedback control
schemes, which correspond respectively to deterministic and stochastic Master
Equation dynamics. For the quantum feedback control scheme with continuous
non-demolition observations we exploit the separation theorem of filtering and
control aspects for quantum stochastic dynamics to derive a generalized
Hamilton-Jacobi-Bellman equation. If the control is restricted to only
Hamiltonian terms this is equivalent to a Hamilton-Jacobi equation with an
extra linear dissipative term. In this work, we consider, in particular, the
case when control is restricted to only observation. A controlled qubit is
considered as an example throughout the development of the formalism. Finally,
we discuss optimum observation strategies to obtain a pure state from a mixed
state of a quantum two-level system.Comment: 11 pages, no figures, published versio
Quantum computing implementations with neutral particles
We review quantum information processing with cold neutral particles, that
is, atoms or polar molecules. First, we analyze the best suited degrees of
freedom of these particles for storing quantum information, and then we discuss
both single- and two-qubit gate implementations. We focus our discussion mainly
on collisional quantum gates, which are best suited for atom-chip-like devices,
as well as on gate proposals conceived for optical lattices. Additionally, we
analyze schemes both for cold atoms confined in optical cavities and hybrid
approaches to entanglement generation, and we show how optimal control theory
might be a powerful tool to enhance the speed up of the gate operations as well
as to achieve high fidelities required for fault tolerant quantum computation.Comment: 19 pages, 12 figures; From the issue entitled "Special Issue on
Neutral Particles
Speeding up the spatial adiabatic passage of matter waves in optical microtraps by optimal control
We numerically investigate the performance of atomic transport in optical
microtraps via the so called spatial adiabatic passage technique. Our analysis
is carried out by means of optimal control methods, which enable us to
determine suitable transport control pulses. We investigate the ultimate limits
of the optimal control in speeding up the transport process in a triple well
configuration for both a single atomic wave packet and a Bose-Einstein
condensate within a regime of experimental parameters achievable with current
optical technology.Comment: 17 pages, 14 figure
Dark solitons in atomic Bose-Einstein condensates: from theory to experiments
This review paper presents an overview of the theoretical and experimental
progress on the study of matter-wave dark solitons in atomic Bose-Einstein
condensates. Upon introducing the general framework, we discuss the statics and
dynamics of single and multiple matter-wave dark solitons in the quasi
one-dimensional setting, in higher-dimensional settings, as well as in the
dimensionality crossover regime. Special attention is paid to the connection
between theoretical results, obtained by various analytical approaches, and
relevant experimental observations.Comment: 82 pages, 13 figures. To appear in J. Phys. A: Math. Theor
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