7,351 research outputs found
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
Constraints on the density dependence of the symmetry energy
Collisions involving 112Sn and 124Sn nuclei have been simulated with the
improved Quantum Molecular Dynamics transport model. The results of the
calculations reproduce isospin diffusion data from two different observables
and the ratios of neutron and proton spectra. By comparing these data to
calculations performed over a range of symmetry energies at saturation density
and different representations of the density dependence of the symmetry energy,
constraints on the density dependence of the symmetry energy at sub-normal
density are obtained. Results from present work are compared to constraints put
forward in other recent analysis.Comment: 8 pages, 4 figures,accepted for publication in Phy. Rev. Let
Ziv-Zakai Error Bounds for Quantum Parameter Estimation
I propose quantum versions of the Ziv-Zakai bounds as alternatives to the
widely used quantum Cram\'er-Rao bounds for quantum parameter estimation. From
a simple form of the proposed bounds, I derive both a "Heisenberg" error limit
that scales with the average energy and a limit similar to the quantum
Cram\'er-Rao bound that scales with the energy variance. These results are
further illustrated by applying the bound to a few examples of optical phase
estimation, which show that a quantum Ziv-Zakai bound can be much higher and
thus tighter than a quantum Cram\'er-Rao bound for states with highly
non-Gaussian photon-number statistics in certain regimes and also stay close to
the latter where the latter is expected to be tight.Comment: v1: preliminary result, 3 pages; v2: major update, 4 pages +
supplementary calculations, v3: another major update, added proof of
"Heisenberg" limit, v4: accepted by PR
The reproductive cycle of the thorny skate (Amblyraja radiata) in the western Gulf of Maine
The thorny skate (Amblyraja radiata) is a large species of
skate that is endemic to the waters of the western north Atlantic in the Gulf of Maine. Because the biomass of thorny skates has recently declined below threshold levels mandated by the Sustainable Fisheries Act, commercial
harvests from this region are prohibited. We have undertaken
a comprehensive study to gain insight into the life history of this skate. The present study describes and
characterizes the reproductive cycle of female and male thorny skates, based on monthly samples taken off the coast of New Hampshire, from May 2001 to May 2003. Gonadosomatic
index (GSI), shell gland weight, follicle size, and egg case formation, were assessed for 48 female skates. In general, these reproductive parameters remained relatively constant throughout most of the year. However, transient but significant increases in shell gland weight and GSI were
obser ved during certain months. Within the cohort of specimens sampled monthly throughout the year, a subset of females always had large preovulatory follicles present in their ovaries. With the exception of June and September specimens, egg cases undergoing various stages of development were observed in the uteri of specimens captured during all other months of the year. For males (n=48), histological stages III through VI (SIII−SVI) of spermatogenesis, GSI, and hepatosomatic index (HSI) were
examined. Although there appeared to be monthly fluctuations in spermatogenesis, GSI, and HSI, no significant differences were found. The production and maintenance of mature spermatocysts (SVI) within the testes was observed throughout the year. These findings collectively indicate that the thorny skate is reproductively active year round
Probing nuclear symmetry energy with the sub-threshold pion production
Within the framework of semiclassical Boltzmann-Uehling-Uhlenbeck (BUU)
transport model, we investigated the effects of symmetry energy on the
sub-threshold pion using the isospin MDI interaction with the stiff and soft
symmetry energies in the central collision of Ca + Ca at the
incident beam energies of 100, 150, 200, 250 and 300 MeV/nucleon, respectively.
We find that the ratio of of sub-threshold charged pion
production is greatly sensitive to the symmetry energy, particularly around 100
MeV/nucleon energies. Large sensitivity of sub-threshold charged pion
production to nuclear symmetry energy may reduce uncertainties of probing
nuclear symmetry energy via heavy-ion collision.Comment: 5 pages, 5 figures, typo corrections, submitted to Chinese Physics
Letter
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