118 research outputs found
Controllability of spin-boson systems
In this paper we study the so-called spin-boson system, namely {a two-level
system} in interaction with a distinguished mode of a quantized bosonic field.
We give a brief description of the controlled Rabi and Jaynes--Cummings models
and we discuss their appearance in the mathematics and physics literature. We
then study the controllability of the Rabi model when the control is an
external field acting on the bosonic part. Applying geometric control
techniques to the Galerkin approximation and using perturbation theory to
guarantee non-resonance of the spectrum of the drift operator, we prove
approximate controllability of the system, for almost every value of the
interaction parameter
Suivi de l'abondance en Trichodesmium spp. (cyanobactéries filamenteuses) et des paramÚtres du milieu lagonaire en baie de Ouinné, Nouvelle-Calédonie : 2 janvier - 3 février 2007
Adiabatic passage and ensemble control of quantum systems
This paper considers population transfer between eigenstates of a finite
quantum ladder controlled by a classical electric field. Using an appropriate
change of variables, we show that this setting can be set in the framework of
adiabatic passage, which is known to facilitate ensemble control of quantum
systems. Building on this insight, we present a mathematical proof of
robustness for a control protocol -- chirped pulse -- practiced by
experimentalists to drive an ensemble of quantum systems from the ground state
to the most excited state. We then propose new adiabatic control protocols
using a single chirped and amplitude shaped pulse, to robustly perform any
permutation of eigenstate populations, on an ensemble of systems with badly
known coupling strengths. Such adiabatic control protocols are illustrated by
simulations achieving all 24 permutations for a 4-level ladder
Nonlinear effect on quantum control for two-level systems
The traditional quantum control theory focuses on linear quantum system. Here
we show the effect of nonlinearity on quantum control of a two-level system, we
find that the nonlinearity can change the controllability of quantum system.
Furthermore, we demonstrate that the Lyapunov control can be used to overcome
this uncontrollability induced by the nonlinear effect.Comment: 4 pages, 5 figure
One hundred second bit-flip time in a two-photon dissipative oscillator
Current implementations of quantum bits (qubits) continue to undergo too many
errors to be scaled into useful quantum machines. An emerging strategy is to
encode quantum information in the two meta-stable pointer states of an
oscillator exchanging pairs of photons with its environment, a mechanism shown
to provide stability without inducing decoherence. Adding photons in these
states increases their separation, and macroscopic bit-flip times are expected
even for a handful of photons, a range suitable to implement a qubit. However,
previous experimental realizations have saturated in the millisecond range. In
this work, we aim for the maximum bit-flip time we could achieve in a
two-photon dissipative oscillator. To this end, we design a Josephson circuit
in a regime that circumvents all suspected dynamical instabilities, and employ
a minimally invasive fluorescence detection tool, at the cost of a two-photon
exchange rate dominated by single-photon loss. We attain bit-flip times of the
order of 100 seconds for states pinned by two-photon dissipation and containing
about 40 photons. This experiment lays a solid foundation from which the
two-photon exchange rate can be gradually increased, thus gaining access to the
preparation and measurement of quantum superposition states, and pursuing the
route towards a logical qubit with built-in bit-flip protection
Newly diagnosed rheumatic heart disease among indigenous populations in the Pacific
Objectives Rheumatic heart disease (RHD) remains the leading acquired heart disease in the young worldwide. We aimed at assessing outcomes and influencing factors in the contemporary era. Methods Hospital-based cohort in a high-income island nation where RHD remains endemic and the population is captive. All patients admitted with newly diagnosed RHD according to World Heart Federation echocardiographic criteria were enrolled (2005â2013). The incidence of major cardiovascular events (MACEs) including heart failure, peripheral embolism, stroke, heart valve intervention and cardiovascular death was calculated, and their determinants identified. Results Of the 396 patients, 43.9% were male with median age 18â
years (IQR 10â40)). 127 (32.1%) patients presented with mild, 131 (33.1%) with moderate and 138 (34.8%) with severe heart valve disease. 205 (51.8%) had features of acute rheumatic fever. 106 (26.8%) presented with at least one MACE. Among the remaining 290 patients, after a median follow-up period of 4.08 (95% CI 1.84 to 6.84) years, 7 patients (2.4%) died and 62 (21.4%) had a first MACE. The annual incidence of first MACE and of heart failure were 59.05â° (95% CI 44.35 to 73.75) and 29.06â° (95% CI 19.29 to 38.82), respectively. The severity of RHD at diagnosis (moderate vs mild HR 3.39 (0.95 to 12.12); severe vs mild RHD HR 10.81 (3.11 to 37.62), p<0.001) and ongoing secondary prophylaxis at follow-up (HR 0.27 (0.12 to 0.63), p=0.01) were the two most influential factors associated with MACE. Conclusions Newly diagnosed RHD is associated with poor outcomes, mainly in patients with moderate or severe valve disease and no secondary prophylaxis
From least action in electrodynamics to magnetomechanical energy -- a review
The equations of motion for electromechanical systems are traced back to the
fundamental Lagrangian of particles and electromagnetic fields, via the Darwin
Lagrangian. When dissipative forces can be neglected the systems are
conservative and one can study them in a Hamiltonian formalism. The central
concepts of generalized capacitance and inductance coefficients are introduced
and explained. The problem of gauge independence of self-inductance is
considered. Our main interest is in magnetomechanics, i.e. the study of systems
where there is exchange between mechanical and magnetic energy. This throws
light on the concept of magnetic energy, which according to the literature has
confusing and peculiar properties. We apply the theory to a few simple
examples: the extension of a circular current loop, the force between parallel
wires, interacting circular current loops, and the rail gun. These show that
the Hamiltonian, phase space, form of magnetic energy has the usual property
that an equilibrium configuration corresponds to an energy minimum.Comment: 29 pages, 9 figures, 65 reference
A review of composite product data interoperability and product life-cycle management challenges in the composites industry
A review of composite product data interoperability and product life-cycle management challenges is presented, which addresses âProduct Life-cycle Managementâ, developments in materials. The urgent need for this is illustrated by the life-cycle management issues faced in modern military aircraft, where in-service failure of composite parts is a problem, not just in terms of engineering understanding, but also in terms of the process for managing and maintaining the fleet. A demonstration of the use of ISO 10303-235 for a range of through-life composite product data is reported. The standardization of the digital representation of data can help businesses to automate data processing. With the development of new materials, the requirements for data information models for materials properties are evolving, and standardization drives transparency, improves the efficiency of data analysis, and enhances data accuracy. Current developments in Information Technology, such as big data analytics methodologies, have the potential to be highly transformative
A study of the deterioration of aged parchment marked with laboratory iron gall inks using FTIR-ATR spectroscopy and micro hot table
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