10,933 research outputs found
Entanglement and spin-squeezing in a network of distant optical lattice clocks
We propose an approach for collective enhancement of precision for remotely
located optical lattice clocks and a way of generation of the
Einstein-Podolsky-Rosen state of remote clocks. Close to Heisenberg scaling of
the clock precision with the number of clocks M can be achieved even for an
optical channel connecting clocks with substantial losses. This scenario
utilizes a collective quantum nondemolition measurement on clocks with parallel
Bloch vectors for enhanced measurement precision. We provide an optimal network
solution for distant clocks as well as for clocks positioned in close proximity
of each other. In the second scenario, we employ collective dissipation to
drive two clocks with oppositely oriented Bloch vectors into a steady state
entanglement. The corresponding EPR entanglement provides enhanced time sharing
beyond the projection noise limit between the two quantum synchronized clocks
protected from eavesdropping, as well as allows better characterization of
systematic effects
Optimal Jackknife for Discrete Time and Continuous Time Unit Root Models
Maximum likelihood estimation of the persistence parameter in the discrete time unit root model is known for suffering from a downward bias. The bias is more pronounced in the continuous time unit root model. Recently Chambers and Kyriacou (2010) introduced a new jackknife method to remove the fiÂ…rst order bias in the estimator of the persistence parameter in a discrete time unit root model. This paper proposes an improved jackknife estimator of the persistence parameter that works for both the discrete time unit root model and the continuous time unit root model. The proposed jackknife estimator is optimal in the sense that it minimizes the variance. Simulations highlight the performance of the proposed method in both contexts. They show that our optimal jackknife reduces the variance of the jackknife method of Chambers and Kyriacou by at least 10% in both cases.Bias reduction, Variance reduction, Vasicek model, Long-span Asymptotics, Autoregression
Prospects for application of ultracold Sr molecules in precision measurements
Precision measurements with ultracold molecules require development of robust
and sensitive techniques to produce and interrogate the molecules. With this
goal, we theoretically analyze factors that affect frequency measurements
between rovibrational levels of the Sr molecule in the electronic ground
state. This measurement can be used to constrain the possible time variation of
the proton-electron mass ratio. Sr is expected to be a strong candidate for
achieving high precision due to the spinless nature and ease of cooling and
perturbation-free trapping of Sr \cite{Zelevinsky2008}. The analysis includes
calculations of two-photon transition dipole moments between deeply and weakly
bound vibrational levels, lifetimes of intermediate excited states, and Stark
shifts of the vibrational levels by the optical lattice field, including
possibilities of Stark-cancellation trapping.Comment: 8 pages, 10 figure
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