859 research outputs found
Observing quantum state diffusion by heterodyne detection of fluorescence
A qubit can relax by fluorescence, which prompts the release of a photon into
its electromagnetic environment. By counting the emitted photons, discrete
quantum jumps of the qubit state can be observed. The succession of states
occupied by the qubit in a single experiment, its quantum trajectory, depends
in fact on the kind of detector. How are the quantum trajectories modified if
one measures continuously the amplitude of the fluorescence field instead?
Using a superconducting parametric amplifier, we have performed heterodyne
detection of the fluorescence of a superconducting qubit. For each realization
of the measurement record, we can reconstruct a different quantum trajectory
for the qubit. The observed evolution obeys quantum state diffusion, which is
characteristic of quantum measurements subject to zero point fluctuations.
Independent projective measurements of the qubit at various times provide a
quantitative validation of the reconstructed trajectories. By exploring the
statistics of quantum trajectories, we demonstrate that the qubit states span a
deterministic surface in the Bloch sphere at each time in the evolution.
Additionally, we show that when monitoring fluorescence, coherent
superpositions are generated during the decay from excited to ground state.
Counterintuitively, measuring light emitted during relaxation can give rise to
trajectories with increased excitation probability.Comment: Supplementary material can be found in the ancillary sectio
A physically-based and fully coupled model of elasto-plasticity and damage for dynamic failure in ductile metals
It is well established that spall fracture and other rapid failures in ductile materials are often dominated by nucleation and growth ofmicro-voids. In the present work, a mechanistic model for failure by cumulative nucleation and growth of voids is fully coupled with the thermoelastoplasticconstitutive equations of the Mechanical Threshold Stress (MTS) which is used to model the evolution of the flow stress. Thedamage modeling includes both ductile and brittle mechanisms. It accounts for the effects of inertia, rate sensitivity, fracture surface energy, andnucleation frequency. The MTS model used for plasticity includes the superposition of different thermal activation barriers for dislocationmotion. Results obtained in the case of uncoupled and coupled model of plasticity and damage from the simulations of the planar impact withcylindrical target, are presented and compared with the experimental results for OFHC copper. This comparison shows the model capabilities inpredicting the experimentally measured free surface velocity profile as well as the observed spall and other damage patterns in the material underimpact loading. These results are obtained using the finite element code Abaqus/Explicit
Using Spontaneous Emission of a Qubit as a Resource for Feedback Control
Persistent control of a transmon qubit is performed by a feedback protocol
based on continuous heterodyne measurement of its fluorescence. By driving the
qubit and cavity with microwave signals whose amplitudes depend linearly on the
instantaneous values of the quadratures of the measured fluorescence field, we
show that it is possible to stabilize permanently the qubit in any targeted
state. Using a Josephson mixer as a phase-preserving amplifier, it was possible
to reach a total measurement efficiency =35%, leading to a maximum of 59%
of excitation and 44% of coherence for the stabilized states. The experiment
demonstrates multiple-input multiple-output analog Markovian feedback in the
quantum regime.Comment: Supplementary material can be found as an ancillary objec
Simulation of the Taylor impact test and analysis of damage evolution using a nucleation and growth based approach
International audienceComputational modeling of the Taylor impact test, using OFHC copper rods are carried out for two impact velocities (260 m/s and 365 m/s). The aim of this work is to demonstrate the efficiency of the recently proposed material model for dynamic plasticity and failure for metals. This model combines the use of a damage approach based on void nucleation and growth, with the Mechanical Threshold Stress (MTS) model for the evolution of the flow stress in isotropic plasticity. The proposed approach is implemented in the finite element code ABAQUS/Explicit via a user material subroutine and the symmetric Taylor impact test, using copper rods, is simulated. The predicted results are compared to the experimental results reported in the open literature and good agreement is found for both shape change and damage distribution
MEMPHYS:A large scale water Cerenkov detector at Fr\'ejus
A water \v{C}erenkov detector project, of megaton scale, to be installed in
the Fr\'ejus underground site and dedicated to nucleon decay, neutrinos from
supernovae, solar and atmospheric neutrinos, as well as neutrinos from a
super-beam and/or a beta-beam coming from CERN, is presented and compared with
competitor projects in Japan and in the USA. The performances of the European
project are discussed, including the possibility to measure the mixing angle
and the CP-violating phase .Comment: 1+33 pages, 14 figures, Expression of Interest of MEMPHYS projec
GPCR-OKB: the G protein coupled receptor oligomer knowledge base
Rapid expansion of available data about G Protein Coupled Receptor (GPCR) dimers/oligomers over the past few years requires an effective system to organize this information electronically. Based on an ontology derived from a community dialog involving colleagues using experimental and computational methodologies, we developed the GPCR-Oligomerization Knowledge Base (GPCR-OKB). GPCR-OKB is a system that supports browsing and searching for GPCR oligomer data. Such data were manually derived from the literature. While focused on GPCR oligomers, GPCR-OKB is seamlessly connected to GPCRDB, facilitating the correlation of information about GPCR protomers and oligomers
Coherence of neutrino flavor mixing in quantum field theory
In the simplistic quantum mechanical picture of flavor mixing, conditions on
the maximum size and minimum coherence time of the source and detector regions
for the observation of interference---as well as the very viability of the
approach---can only be argued in an ad hoc way from principles external to the
formalism itself. To examine these conditions in a more fundamental way, the
quantum field theoretical -matrix approach is employed in this paper,
without the unrealistic assumption of microscopic stationarity. The fully
normalized, time-dependent neutrino flavor mixing event rates presented here
automatically reveal the coherence conditions in a natural, self-contained, and
physically unambiguous way, while quantitatively describing the transition to
their failure.Comment: 12 pages, submitted to Phys. Rev.
The Offline Software Framework of the Pierre Auger Observatory
To be published in the ProceedingsInternational audienceThe Pierre Auger Observatory is designed to unveil the nature and the origins of the highest energy cosmic rays. The large and geographically dispersed collaboration of physicists and the wide-ranging collection of simulation and reconstruction tasks pose some special challenges for the offline analysis software. We have designed and implemented a general purpose framework which allows collaborators to contribute algorithms and sequencing instructions to build up the variety of applications they require. The framework includes machinery to manage these user codes, to organize the abundance of user-contributed configuration files, to facilitate multi-format file handling, and to provide access to event and time-dependent detector information which can reside in various data sources. A number of utilities are also provided, including a novel geometry package which allows manipulation of abstract geometrical objects independent of coordinate system choice. The framework is implemented in C++, and takes advantage of object oriented design and common open source tools, while keeping the user side simple enough for C++ novices to learn in a reasonable time. The distribution system incorporates unit and acceptance testing in order to support rapid development of both the core framework and contributed user code
Electron neutrino tagging through tertiary lepton detection
We discuss an experimental technique aimed at tagging electron neutrinos in
multi-GeV artificial sources on an event-by-event basis. It exploits in a novel
manner calorimetric and tracking technologies developed in the framework of the
LHC experiments and of rare kaon decay searches. The setup is suited for
slow-extraction, moderate power beams and it is based on an instrumented decay
tunnel equipped with tagging units that intercept secondary and tertiary
leptons from the bulk of undecayed \pi^+ and protons. We show that the taggers
are able to reduce the \nue contamination originating from K_e3 decays by about
one order of magnitude. Only a limited suppression (~60%) is achieved for \nue
produced by the decay-in-flight of muons; for low beam powers, similar
performance as for K_e3 can be reached supplementing the tagging system with an
instrumented beam dump.Comment: 19 pages, 7 figures; minor changes, version to appear in EPJ
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