473 research outputs found
High-finesse optical quantum gates for electron spins in artificial molecules
A doped semiconductor double-quantum-dot molecule is proposed as a qubit
realization. The quantum information is encoded in the electron spin, thus
benefiting from the long relevant decoherence times; the enhanced flexibility
of the molecular structure allows to map the spin degrees of freedom onto the
orbital ones and vice versa, and opens the possibility for high-finesse
(conditional and unconditional) quantum gates by means of stimulated Raman
adiabatic passage.Comment: To appear in Phys. Rev. Let
Influence of Simulation Parameters in the Combined Loading Compression Testing of CFRP Specimens
In this paper a sensitivity study of a FEM model representing a carbon/epoxy composite material tested in Combined Loading Compression (CLC) is presented and the results are compared to experimental results. The present study aims to simulate the failure of composite materials when subjected to compression and crush loading conditions. This is required as a first step of a Building-Block Approach towards full-scale modelling of complex structures. In the experimental part of the work, a laminate panel was manufactured with carbon unidirectional prepreg (Deltapreg UTS-300-DT120-37EF) in a cross-ply, balanced and symmetric stacking sequence, cured in autoclave at 120°C and 5 bar for 90 min. A number of six samples, extracted from the panel, were tested in compression following ASTM D6641/D6641M-16. Numerical simulations have been implemented by means of the commercial software, ESI-VPS PAM CRASH. Boundary conditions, specimens' dimensions and material properties emulated real test conditions. A sensitivity study was performed on critical simulation parameters: the effect of mesh size and number of shell surfaces representing the composite stacking sequence was initially investigated. Furthermore, the specimen failure mode was inspected by the application of TIED links between the composite plies. Numerical results have been compared with experimental data and the comparison provided references for testing scale-up in the Building-Block Approach
The blockage problem
We investigate the totally asymmetric exclusion process on Z, with the jump
rate at site i given by r_i=1 for i nonzero, r_0=r. It is easy to see that the
maximal stationary current j(r) is nondecreasing in r and that j(r)=1/4 for
r>=1; it is a long outstanding problem to determine whether or not the critical
value r_c of r such that j(r)=1/4 for r>r_c is strictly less than 1. Here we
present a heuristic argument, based on the analysis of the first sixteen terms
in a formal power series expansion of j(r) obtained from finite volume systems,
that r_c=1 and that for r less than 1 and near 1, j(r) behaves as
1/4-\gamma\exp[-{a/(1-r)}] with a approximately equal to 2. We also give some
new exact results about this system; in particular we prove that j(r)=J_max(r),
with J_max(r) the hydrodynamic maximal current defined by Seppalainen, and thus
establish continuity of j(r). Finally we describe a related exactly solvable
model, a semi-infinite system in which the site i=0 is always occupied. For
that system, the critical r is 1/2 and the analogue j_s(r) of j(r) satisfies
j_s(r)=r(1-r) for r<=1/2; j_s(r) is the limit of finite volume currents inside
the curve |r(1-r)|=1/4 in the complex r plane and we suggest that analogous
behavior may hold for the original system.Comment: 23 pages, 6 figure
Numerical Investigation of Al-Reinforced CFRP Composite under Low-Velocity Impact
Fibre-reinforced composite materials are widespread in lightweight, high-performance applications. However, polymeric composites generally exhibit a brittle behaviour, which makes them susceptible to impact damage. Even low-velocity impacts can produce delaminations, which cause a substantial reduction of the compressive mechanical properties. Metallic layers have been embedded in composite laminates with the aim to improve their fracture behaviour: aluminium plies can be employed to increase the indentation resistance of Carbon Fibre Reinforced Polymers (CFRP) specimens. For this reason, hybrid fibre-metal laminates are expected to be a viable solution to reduce the damage caused by low-velocity impacts. In this work, CFRP specimens reinforced with aluminium plies were modelled using the finite element method and a cohesive zone model. Cohesive elements based on a traction-separation formulation were embedded at each ply-to-ply interface to enforce delamination damage. Different configurations of the Al reinforcements were studied by varying the position of the aluminium layers between the CFRP plies
Coherently coupling distinct spin ensembles through a high-Tc superconducting resonator
The problem of coupling multiple spin ensembles through cavity photons is revisited by using (3,5-dichloro-4- pyridyl)bis(2,4,6-trichlorophenyl) methyl (PyBTM) organic radicals and a high-T-c superconducting coplanar resonator. An exceptionally strong coupling is obtained and up to three spin ensembles are simultaneously coupled. The ensembles are made physically distinguishable by chemically varying the g factor and by exploiting the inhomogeneities of the applied magnetic field. The coherent mixing of the spin and field modes is demonstrated by the observed multiple anticrossing, along with the simulations performed within the input-output formalism, and quantified by suitable entropic measures
Toward Hole-Spin Qubits in Si p -MOSFETs within a Planar CMOS Foundry Technology
Hole spins in semiconductor quantum dots represent a viable route for the implementation of electrically controlled qubits. In particular, the qubit implementation based on Si p-MOSFETs offers great potentialities in terms of integration with the control electronics and long-term scalability. Moreover, the future down scaling of these devices will possibly improve the performance of both the classical (control) and quantum components of such monolithically integrated circuits. Here, we use a multiscale approach to simulate a hole-spin qubit in a down-scaled Si-channel p-MOSFET, the structure of which is based on a commercial 22-nm fully depleted silicon-on-insulator device. Our calculations show the formation of well-defined hole quantum dots within the Si channel and the possibility of a general electrical control, with Rabi frequencies of the order of 100MHz for realistic field values. A crucial role of the channel aspect ratio is also demonstrated, as well as the presence of a favorable parameter range for the qubit manipulation
Resonant nature of phonon-induced damping of Rabi oscillations in quantum dots
Optically controlled coherent dynamics of charge (excitonic) degrees of
freedom in a semiconductor quantum dot under the influence of lattice dynamics
(phonons) is discussed theoretically. We show that the dynamics of the lattice
response in the strongly non-linear regime is governed by a semiclassical
resonance between the phonon modes and the optically driven dynamics. We stress
on the importance of the stability of intermediate states for the truly
coherent control.Comment: 4 pages, 2 figures; final version; moderate changes, new titl
Exploiting exciton-exciton interactions in semiconductor quantum dots for quantum-information processing
We propose an all-optical implementation of quantum-information processing in
semiconductor quantum dots, where electron-hole excitations (excitons) serve as
the computational degrees of freedom (qubits). We show that the strong dot
confinement leads to an overall enhancement of Coulomb correlations and to a
strong renormalization of the excitonic states, which can be exploited for
performing conditional and unconditional qubit operations.Comment: 5 pages revtex, 2 encapsulated postscript figures. Accepted for
publication in Phys. Rev. B (Rapid Communication
Time-resolved spectroscopy of multi-excitonic decay in an InAs quantum dot
The multi-excitonic decay process in a single InAs quantum dot is studied
through high-resolution time-resolved spectroscopy. A cascaded emission
sequence involving three spectral lines is seen that is described well over a
wide range of pump powers by a simple model. The measured biexcitonic decay
rate is about 1.5 times the single-exciton decay rate. This ratio suggests the
presence of selection rules, as well as a significant effect of the Coulomb
interaction on the biexcitonic wavefunction.Comment: one typo fixe
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