54 research outputs found
Collective luminescence and phonon-induced processes in double quantum dots
We study the evolution of a quantum state of a double quantum dot system
interacting with the electromagnetic environment and with the lattice modes, in
the presence of a coupling between the two dots. We propose a unified approach
to the simulation of the system evolution under joint impact of the two
reservoirs. We discuss the sub- and superradiant radiative decay of the system,
the phonon-induced decay of entanglement between the dots, and the transfer of
excitation between them.Comment: "Jaszowiec 2009" conferenc
Theory of nonlinear optical response of ensembles of double quantum dots
We study theoretically the time-resolved four-wave mixing (FWM) response of
an ensemble of pairs of quantum dots undergoing radiative recombination. At
short (picosecond) delay times, the response signal shows beats that may be
dominated by the subensemble of resonant pairs, which gives access to the
information on the interdot coupling. At longer delay times, the decay of the
FWM signal is governed by two rates which result from the collective
interaction between the two dots and the radiation modes. The two rates
correspond to the subradiant and super-radiant components in the radiative
decay. Coupling between the dots enhances the collective effects and makes them
observable even when the average energy mismatch between the dots is relatively
large.Comment: 8 pages, 3 figures; moderately modifie
A Hybrid Approach to the Optimization of Multiechelon Systems
In freight transportation there are two main distribution strategies: direct shipping and multiechelon distribution. In the direct shipping, vehicles, starting from a depot, bring their freight directly to the destination, while in the multiechelon systems, freight is delivered from the depot to the customers through an intermediate points. Multiechelon systems are particularly useful for logistic issues in a competitive environment. The paper presents a concept and application of a hybrid approach to modeling and optimization of the Multi-Echelon Capacitated Vehicle Routing Problem. Two ways of mathematical programming (MP) and constraint logic programming (CLP) are integrated in one environment. The strengths of MP and CLP in which constraints are treated in a different way and different methods are implemented and combined to use the strengths of both. The proposed approach is particularly important for the discrete decision models with an objective function and many discrete decision variables added up in multiple constraints. An implementation of hybrid approach in the ECLiPSe system using Eplex library is presented. The Two-Echelon Capacitated Vehicle Routing Problem (2E-CVRP) and its variants are shown as an illustrative example of the hybrid approach. The presented hybrid approach will be compared with classical mathematical programming on the same benchmark data sets
Phonon effects on the radiative recombination of excitons in double quantum dots
We study theoretically the radiative recombination of excitons in double
quantum dots in the presence of carrier-phonon coupling. We show that the
phonon-induced pure dephasing effects and transitions between the exciton
states strongly modify the spontaneous emission process and make it sensitive
to temperature, which may lead to non-monotonic temperature dependence of the
time-resolved luminescence. We show also that under specific resonance
conditions the biexcitonic interband polarization can be coherently transferred
to the excitonic one, leading to an extended life time of the total coherent
polarization, which is reflected in the nonlinear optical spectrum of the
system. We study the stability of this effect against phonon-induced
decoherence.Comment: 10 pages, 7 figure
Collective fluorescence and decoherence of a few nearly identical quantum dots
We study the collective interaction of excitons in closely spaced artificial
molecules and arrays of nearly identical quantum dots with the electromagnetic
modes. We discuss how collective fluorescence builds up in the presence of a
small mismatch of the transition energy. We show that a superradiant state of a
single exciton in a molecule of two dots with realistic energy mismatch
undergoes a two-rate decay. We analyze also the stability of subdecoherent
states for non-identical systems.Comment: 7 pages, 5 figure
A Hybrid Method for Modeling and Solving Supply Chain Optimization Problems with Soft and Logical Constraints
This paper presents a hybrid method for modeling and solving supply chain optimization problems with soft, hard, and logical constraints. Ability to implement soft and logical constraints is a very important functionality for supply chain optimization models. Such constraints are particularly useful for modeling problems resulting from commercial agreements, contracts, competition, technology, safety, and environmental conditions. Two programming and solving environments, mathematical programming (MP) and constraint logic programming (CLP), were combined in the hybrid method. This integration, hybridization, and the adequate multidimensional transformation of the problem (as a presolving method) helped to substantially reduce the search space of combinatorial models for supply chain optimization problems. The operation research MP and declarative CLP, where constraints are modeled in different ways and different solving procedures are implemented, were linked together to use the strengths of both. This approach is particularly important for the decision and combinatorial optimization models with the objective function and constraints, there are many decision variables, and these are summed (common in manufacturing, supply chain management, project management, and logistic problems). The ECLiPSe system with Eplex library was proposed to implement a hybrid method. Additionally, the proposed hybrid transformed model is compared with the MILP-Mixed Integer Linear Programming model on the same data instances. For illustrative models, its use allowed finding optimal solutions eight to one hundred times faster and reducing the size of the combinatorial problem to a significant extent
- …