349 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
Exploring constrained quantum control landscapes
The broad success of optimally controlling quantum systems with external
fields has been attributed to the favorable topology of the underlying control
landscape, where the landscape is the physical observable as a function of the
controls. The control landscape can be shown to contain no suboptimal trapping
extrema upon satisfaction of reasonable physical assumptions, but this
topological analysis does not hold when significant constraints are placed on
the control resources. This work employs simulations to explore the topology
and features of the control landscape for pure-state population transfer with a
constrained class of control fields. The fields are parameterized in terms of a
set of uniformly spaced spectral frequencies, with the associated phases acting
as the controls. Optimization results reveal that the minimum number of phase
controls necessary to assure a high yield in the target state has a special
dependence on the number of accessible energy levels in the quantum system,
revealed from an analysis of the first- and second-order variation of the yield
with respect to the controls. When an insufficient number of controls and/or a
weak control fluence are employed, trapping extrema and saddle points are
observed on the landscape. When the control resources are sufficiently
flexible, solutions producing the globally maximal yield are found to form
connected `level sets' of continuously variable control fields that preserve
the yield. These optimal yield level sets are found to shrink to isolated
points on the top of the landscape as the control field fluence is decreased,
and further reduction of the fluence turns these points into suboptimal
trapping extrema on the landscape. Although constrained control fields can come
in many forms beyond the cases explored here, the behavior found in this paper
is illustrative of the impacts that constraints can introduce.Comment: 10 figure
Probing the dynamical and X-ray mass proxies of the cluster of galaxies Abell S1101
Context: The galaxy cluster Abell S1101 (S1101 hereafter) deviates
significantly from the X-ray luminosity versus velocity dispersion relation
(L-sigma) of galaxy clusters in our previous study. Given reliable X-ray
luminosity measurement combining XMM-Newton and ROSAT, this could most likely
be caused by the bias in the velocity dispersion due to interlopers and low
member statistic in the previous sample of member galaxies, which was solely
based on 20 galaxy redshifts drawn from the literature. Aims: We intend to
increase the galaxy member statistic to perform a precision measurement of the
velocity dispersion and dynamical mass of S1101. We aim for a detailed
substructure and dynamical state characterization of this cluster, and a
comparison of mass estimates derived from (i) the velocity dispersion (M_vir),
(ii) the caustic mass computation (M_caustic), and (iii) mass proxies from
X-ray observations and the Sunyaev-Zeldovich (SZ) effect. Methods: We carried
out new optical spectroscopic observations of the galaxies in this cluster
field with VIMOS, obtaining a sample of ~60 member galaxies for S1101. We
revised the cluster redshift and velocity dispersion measurements based on this
sample and also applied the Dressler-Shectman substructure test. Results: The
completeness of cluster members within r200 was significantly improved for this
cluster. Tests for dynamical substructure did not show evidence for major
disturbances or merging activities in S1101. We find good agreement between the
dynamical cluster mass measurements and X-ray mass estimates which confirms the
relaxed state of the cluster displayed in the 2D substructure test. The SZ mass
proxy is slightly higher than the other estimates. The updated measurement of
the velocity dispersion erased the deviation of S1101 in the L-sigma relation.Comment: 17 pages, 7 figures, 5 table
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