189,565 research outputs found
Vibration-enhanced quantum transport
In this paper, we study the role of collective vibrational motion in the
phenomenon of electronic energy transfer (EET) along a chain of coupled
electronic dipoles with varying excitation frequencies. Previous experimental
work on EET in conjugated polymer samples has suggested that the common
structural framework of the macromolecule introduces correlations in the energy
gap fluctuations which cause coherent EET. Inspired by these results, we
present a simple model in which a driven nanomechanical resonator mode
modulates the excitation energy of coupled quantum dots and find that this can
indeed lead to an enhancement in the transport of excitations across the
quantum network. Disorder of the on-site energies is a key requirement for this
to occur. We also show that in this solid state system phase information is
partially retained in the transfer process, as experimentally demonstrated in
conjugated polymer samples. Consequently, this mechanism of vibration enhanced
quantum transport might find applications in quantum information transfer of
qubit states or entanglement.Comment: 7 pages, 6 figures, new material, included references, final
published versio
INVESTIGATING THE POWER IN FREIGHT TRANSPORT COMMUNICATION NETWORK STRUCTURE
The business of freight transportation is undergoing a technological revolution at it moves toward the 21st century. New technologies are being developed and adopted in each mode of freight transportation. The one technology that affects all modes is information technology. Information technology related to the coordination of logistics and supply chain management, has the capability of affecting all the modes in a similar way. This technology in the form of electronic data interchange has begun to automate, and reduce the costs of, paper flow required to move goods from shippers, through carriers and transfer points, to consignees. Surveys of the freight transportation industry indicate that the adoption of EDI has not been nearly universal in any dimension. The paper investigates the structure of the communication system used for transport supply chain.POWER electronic commerce freight transport network structure
Atomistic simulations of adiabatic coherent electron transport in triple donor systems
A solid-state analogue of Stimulated Raman Adiabatic Passage can be
implemented in a triple well solid-state system to coherently transport an
electron across the wells with exponentially suppressed occupation in the
central well at any point of time. Termed coherent tunneling adiabatic passage
(CTAP), this method provides a robust way to transfer quantum information
encoded in the electronic spin across a chain of quantum dots or donors. Using
large scale atomistic tight-binding simulations involving over 3.5 million
atoms, we verify the existence of a CTAP pathway in a realistic solid-state
system: gated triple donors in silicon. Realistic gate profiles from commercial
tools were combined with tight-binding methods to simulate gate control of the
donor to donor tunnel barriers in the presence of cross-talk. As CTAP is an
adiabatic protocol, it can be analyzed by solving the time independent problem
at various stages of the pulse - justifying the use of time-independent
tight-binding methods to this problem. Our results show that a three donor CTAP
transfer, with inter-donor spacing of 15 nm can occur on timescales greater
than 23 ps, well within experimentally accessible regimes. The method not only
provides a tool to guide future CTAP experiments, but also illuminates the
possibility of system engineering to enhance control and transfer times.Comment: 8 pages, 5 figure
Adiabatic entanglement transport in Rydberg aggregates
We consider the interplay between excitonic and atomic motion in a regular,
flexible chain of Rydberg atoms, extending our recent results on entanglement
transport in Rydberg chains [W\"uster et al., Phys.Rev.Lett 105 053004 (2010)].
In such a Rydberg chain, similar to molecular aggregates, an electronic
excitation is delocalised due to long range dipole-dipole interactions among
the atoms. The transport of an exciton that is initially trapped by a chain
dislocation is strongly coupled to nuclear dynamics, forming a localised pulse
of combined excitation and displacement. This pulse transfers entanglement
between dislocated atoms adiabatically along the chain. Details about the
interaction and the preparation of the initial state are discussed. We also
present evidence that the quantum dynamics of this complex many-body problem
can be accurately described by selected quantum-classical methods, which
greatly simplify investigations of excitation transport in flexible chains
Low Temperature Electronic Transport and Electron Transfer through Organic Macromolecules
It is shown that at low temperatures and moderate electron dephasing the
electron transmission function reveales a structure containing information
about donor/acceptor sites effectively participating in the electron transfer
(ET) processes and primary pathways of electrons tunneling through molecular
bridges in macromolecules. This important information can be obtained as a
result of analysis of experimental low temperature current-voltage
characteristics for chosen molecules.Comment: 4 pages, 1 figure, text revise
Low Temperature Electronic Transport through Macromolecules and Characteristics of Intramolecular Electron Transfer
A theory of electronic transport through molecular wires is applied to
analyze characteristics of a long-range electron transfer (ET) through
molecular bridges in macromolecules with complex donor/acceptor subsystems.
Assuming a coherent electron tunneling through the bridge to be the predominant
mechanism of ET at low temperatures it is shown that low temperature
current-voltage curves can exhibit a step-like structure, which contains
information concerning intrinsic features of ET processes such as the effect of
donor/acceptor coupling to the bridge and primary pathways of electrons
tunneling through the bridge. By contacting the proposed theoretical analysis
with such experimental data a variety of valuable characteristics of long-range
intramolecular ET can be identified. Analytical and numerical results are
presented. Using the Buttiker dephasing model within the scattering matrix
formalism we analyze dephasing effects, and we show that these effects could be
reduced enough to allow the structure of the electron transmission function to
be exposed in the experiments on the electronic transport through
macromolecules.Comment: 9 pages, 2 figures, text revise
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