876 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
Vanishing quantum discord is necessary and sufficient for completely positive maps
Two long standing open problems in quantum theory are to characterize the
class of initial system-bath states for which quantum dynamics is equivalent to
(1) a map between the initial and final system states, and (2) a completely
positive (CP) map. The CP map problem is especially important, due to the
widespread use of such maps in quantum information processing and open quantum
systems theory. Here we settle both these questions by showing that the answer
to the first is "all", with the resulting map being Hermitian, and that the
answer to the second is that CP maps arise exclusively from the class of
separable states with vanishing quantum discord.Comment: 4 pages, no figures. v2: Accepted for publication in Phys. Rev. Let
Relation between parvovirus B19 infection and fetal mortality and spontaneous abortion
Background: Infection with parvovirus B19 may cause fetal losses including spontaneous abortion, intrauterine fetal death and non-immune hydrops fetalis. The aim of this study is to determine the frequency of parvovirus B19 in formalin fixed placental tissues in lost fetuses using real-time PCR method. Methods: In this cross-sectional study, 100 formalin fixed placental tissues with unknown cause of fetal death were determined using real-time PCR method after DNA extraction. Results: Six out of 100 cases (6) were positive for parvovirus B19 using real-time PCR. Gestational age of all positive cases was less than 20 weeks with a mean of 12.3 weeks. Three cases have a history of abortion and all of positive cases were collected in spring. Mean age of positive cases were 28 years. Conclusion: Parvovirus B19 during pregnancy can infect red precursor cells and induces apoptosis or lyses these cells that resulting in anemia and congestive heart failure leading to fetal death. Management of parvovirus B19 infection in pregnant women is important because immediate diagnosis and transfusion in hydropsic fetuses can decrease the risk of fetal death
Locally Optimal Control of Quantum Systems with Strong Feedback
For quantum systems with high purity, we find all observables that, when
continuously monitored, maximize the instantaneous reduction in the von Neumann
entropy. This allows us to obtain all locally optimal feedback protocols with
strong feedback, and explicit expressions for the best such protocols for
systems of size N <= 4. We also show that for a qutrit the locally optimal
protocol is the optimal protocol for a given range of control times, and derive
an upper bound on all optimal protocols with strong feedback.Comment: 4 pages, Revtex4. v2: published version (some errors corrected
The galaxy rotation curves in the modified gravity formalism
Astronomical data have shown that the galaxy rotation curves are mostly flat
in the far distance of the galactic cores, which reveals the insufficiency of
our knowledges about how gravity works in these regimes. In this paper we
introduce a resolution of this issue from the modified gravity
formalism perspective. By investigating two classes of models with separable
(minimal coupling model) and inseparable (non-minimal coupling model) parts of
the Ricci scalar and trace of the energy-momentum tensor , we find that
only in the latter models it is possible to attain flat galaxy rotation curves.Comment: 9 pages, 4 figure
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