470 research outputs found
A posteriori analysis of discontinuous galerkin schemes for systems of hyperbolic conservation laws
In this work we construct reliable a posteriori estimates for some semi- (spatially) discrete discontinuous Galerkin schemes applied to nonlinear systems of hyperbolic conservation laws. We make use of appropriate reconstructions of the discrete solution together with the relative entropy stability framework, which leads to error control in the case of smooth solutions. The methodology we use is quite general and allows for a posteriori control of discontinuous Galerkin schemes with standard flux choices which appear in the approximation of conservation laws. In addition to the analysis, we conduct some numerical benchmarking to test the robustness of the resultant estimator
Robust Quantum Communication Using A Polarization-Entangled Photon Pair
Noise and imperfection of realistic devices are major obstacles for
implementing quantum cryptography. In particular birefringence in optical
fibers leads to decoherence of qubits encoded in polarization of photon. We
show how to overcome this problem by doing single qubit quantum communication
without a shared spatial reference frame and precise timing. Quantum
information will be encoded in pair of photons using ``tag'' operations which
corresponds to the time delay of one of the polarization modes. This method is
robust against the phase instability of the interferometers despite the use of
time-bins. Moreover synchronized clocks are not required in the ideal situation
no photon loss case as they are only necessary to label the different encoded
qubits.Comment: 4 pages, 2 figure
Effect of nucleon exchange on projectile multifragmentation in the reactions of 28Si + 112Sn and 124Sn at 30 and 50 MeV/nucleon
Multifragmentation of quasiprojectiles was studied in reactions of 28Si beam
with 112Sn and 124Sn targets at projectile energies 30 and 50 MeV/nucleon. The
quasiprojectile observables were reconstructed using isotopically identified
charged particles with Z_f <= 5 detected at forward angles. The nucleon
exchange between projectile and target was investigated using isospin and
excitation energy of reconstructed quasiprojectile. For events with total
reconstructed charge equal to the charge of the beam (Z_tot = 14) the influence
of beam energy and target isospin on neutron transfer was studied in detail.
Simulations employing subsequently model of deep inelastic transfer,
statistical model of multifragmentation and software replica of FAUST detector
array were carried out. A concept of deep inelastic transfer provides good
description of production of highly excited quasiprojectiles. The isospin and
excitation energy of quasiprojectile were described with good overall
agreement. The fragment multiplicity, charge and isospin were reproduced
satisfactorily. The range of contributing impact parameters was determined
using backtracing procedure.Comment: 11 pages, 8 Postscript figures, LaTeX, to appear in Phys. Rev. C (
Dec 2000
Experimental Implementation of Discrete Time Quantum Random Walk on an NMR Quantum Information Processor
We present an experimental implementation of the coined discrete time quantum
walk on a square using a three qubit liquid state nuclear magnetic resonance
(NMR) quantum information processor (QIP). Contrary to its classical
counterpart, we observe complete interference after certain steps and a
periodicity in the evolution. Complete state tomography has been performed for
each of the eight steps making a full period. The results have extremely high
fidelity with the expected states and show clearly the effects of quantum
interference in the walk. We also show and discuss the importance of choosing a
molecule with a natural Hamiltonian well suited to NMR QIP by implementing the
same algorithm on a second molecule. Finally, we show experimentally that
decoherence after each step makes the statistics of the quantum walk tend to
that of the classical random walk.Comment: revtex4, 8 pages, 6 figures, submitted to PR
Energy and angular momentum sharing in dissipative collisions
Primary and secondary masses of heavy reaction products have been deduced
from kinematics and E-ToF measurements, respectively, for the direct and
reverse collisions of 93Nb and 116Sn at 25 AMeV. Light charged particles have
also been measured in coincidence with the heavy fragments.
Direct experimental evidence of the correlation of energy-sharing with net
mass transfer has been found using the information from both the heavy
fragments and the light charged particles.
The ratio of Hydrogen and Helium multiplicities points to a further
correlation of angular momentum sharing with net mass transfer.Comment: 21 pages, 20 figures. Submitted to European Physics Journal
Randomized benchmarking of single and multi-qubit control in liquid-state NMR quantum information processing
Being able to quantify the level of coherent control in a proposed device
implementing a quantum information processor (QIP) is an important task for
both comparing different devices and assessing a device's prospects with
regards to achieving fault-tolerant quantum control. We implement in a
liquid-state nuclear magnetic resonance QIP the randomized benchmarking
protocol presented by Knill et al (PRA 77: 012307 (2008)). We report an error
per randomized pulse of with a
single qubit QIP and show an experimentally relevant error model where the
randomized benchmarking gives a signature fidelity decay which is not possible
to interpret as a single error per gate. We explore and experimentally
investigate multi-qubit extensions of this protocol and report an average error
rate for one and two qubit gates of for a three
qubit QIP. We estimate that these error rates are still not decoherence limited
and thus can be improved with modifications to the control hardware and
software.Comment: 10 pages, 6 figures, submitted versio
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