23,174 research outputs found
Numerical Evidence for Robustness of Environment-Assisted Quantum Transport
Recent theoretical studies show that decoherence process can enhance
transport efficiency in quantum systems. This effect is known as
environment-assisted quantum transport (ENAQT). The role of ENAQT in optimal
quantum transport is well investigated, however, it is less known how robust
ENAQT is with respect to variations in the system or its environment
characteristic. Toward answering this question, we simulated excitonic energy
transfer in Fenna-Matthews-Olson (FMO) photosynthetic complex. We found that
ENAQT is robust with respect to many relevant parameters of environmental
interactions and Frenkel-exciton Hamiltonian including reorganization energy,
bath frequency cutoff, temperature, and initial excitations, dissipation rate,
trapping rate, disorders, and dipole moments orientations. Our study suggests
that the ENAQT phenomenon can be exploited in robust design of highly efficient
quantum transport systems.Comment: arXiv admin note: substantial text overlap with arXiv:1104.481
Kinetic Monte Carlo simulations inspired by epitaxial graphene growth
Graphene, a flat monolayer of carbon atoms packed tightly into a two
dimensional hexagonal lattice, has unusual electronic properties which have
many promising nanoelectronic applications. Recent Low Energy Electron
Microscopy (LEEM) experiments show that the step edge velocity of epitaxially
grown 2D graphene islands on Ru(0001) varies with the fifth power of the
supersaturation of carbon adatoms. This suggests that graphene islands grow by
the addition of clusters of five atoms rather than by the usual mechanism of
single adatom attachment.
We have carried out Kinetic Monte Carlo (KMC) simulations in order to further
investigate the general scenario of epitaxial growth by the attachment of
mobile clusters of atoms. We did not seek to directly replicate the Gr/Ru(0001)
system but instead considered a model involving mobile tetramers of atoms on a
square lattice. Our results show that the energy barrier for tetramer break up
and the number of tetramers that must collide in order to nucleate an immobile
island are the important parameters for determining whether, as in the
Gr/Ru(0001) system, the adatom density at the onset of island nucleation is an
increasing function of temperature. A relatively large energy barrier for
adatom attachment to islands is required in order for our model to produce an
equilibrium adatom density that is a large fraction of the nucleation density.
A large energy barrier for tetramer attachment to islands is also needed for
the island density to dramatically decrease with increasing temperature. We
show that islands grow with a velocity that varies with the fourth power of the
supersaturation of adatoms when tetramer attachment is the dominant process for
island growth
Global crop production forecasting data system analysis
The author has identified the following significant results. Findings led to the development of a theory of radiometric discrimination employing the mathematical framework of the theory of discrimination between scintillating radar targets. The theory indicated that the functions which drive accuracy of discrimination are the contrast ratio between targets, and the number of samples, or pixels, observed. Theoretical results led to three primary consequences, as regards the data system: (1) agricultural targets must be imaged at correctly chosen times, when the relative evolution of the crop's development is such as to maximize their contrast; (2) under these favorable conditions, the number of observed pixels can be significantly reduced with respect to wall-to-wall measurements; and (3) remotely sensed radiometric data must be suitably mixed with other auxiliary data, derived from external sources
Capacity of nonlinear bosonic systems
We analyze the role of nonlinear Hamiltonians in bosonic channels.
We show that the information capacity as a function of the channel energy is
increased with respect to the corresponding linear case, although only when the
energy used for driving the nonlinearity is not considered as part of the
energetic cost and when dispersive effects are negligible.Comment: 6 pages, 3 figure
Gravity gradient preliminary investigations on exhibit ''A'' Final report
Quartz microbalance gravity gradiometer performance test
Information rate of waveguide
We calculate the communication capacity of a broadband electromagnetic
waveguide as a function of its spatial dimensions and input power. We analyze
the two cases in which either all the available modes or only a single
directional mode are employed. The results are compared with those for the free
space bosonic channel.Comment: 5 pages, 2 figures. Revised version (minor changes
Cost/benefit analysis for the Operational Applications of Satellite Snowcover Observations (OASSO)
The author has identified the following significant results. The total cost associated with satellite snow cover area measurement (SATSCAM) in the Colorado ASVT was 493k. The estimated total benefits to hydroeletric energy production is 38m, with the Lower Colorado region receiving the largest per acre benefit and the Pacific Northwest receiving the lowest
A quantum-mechanical Maxwell's demon
A Maxwell's demon is a device that gets information and trades it in for
thermodynamic advantage, in apparent (but not actual) contradiction to the
second law of thermodynamics. Quantum-mechanical versions of Maxwell's demon
exhibit features that classical versions do not: in particular, a device that
gets information about a quantum system disturbs it in the process. In
addition, the information produced by quantum measurement acts as an additional
source of thermodynamic inefficiency. This paper investigates the properties of
quantum-mechanical Maxwell's demons, and proposes experimentally realizable
models of such devices.Comment: 13 pages, Te
Quantum theory of optical temporal phase and instantaneous frequency. II. Continuous time limit and state-variable approach to phase-locked loop design
We consider the continuous-time version of our recently proposed quantum
theory of optical temporal phase and instantaneous frequency [Tsang, Shapiro,
and Lloyd, Phys. Rev. A 78, 053820 (2008)]. Using a state-variable approach to
estimation, we design homodyne phase-locked loops that can measure the temporal
phase with quantum-limited accuracy. We show that post-processing can further
improve the estimation performance, if delay is allowed in the estimation. We
also investigate the fundamental uncertainties in the simultaneous estimation
of harmonic-oscillator position and momentum via continuous optical phase
measurements from the classical estimation theory perspective. In the case of
delayed estimation, we find that the inferred uncertainty product can drop
below that allowed by the Heisenberg uncertainty relation. Although this result
seems counter-intuitive, we argue that it does not violate any basic principle
of quantum mechanics.Comment: 11 pages, 6 figures, v2: accepted by PR
Analog quantum error correction
Quantum error-correction routines are developed for continuous quantum
variables such as position and momentum. The result of such analog quantum
error correction is the construction of composite continuous quantum variables
that are largely immune to the effects of noise and decoherence.Comment: Ten pages, Te
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