Long-range potentials and (n−1)d+ns(n-1)d+ns molecular resonances in an ultracold rydberg gas

We have calculated long-range molecular potentials of the $0_g^{+}$, $0_u^{-}$ and $1_u$ symmetries between highly-excited rubidium atoms. Strong $np+np$ potentials characterized by these symmetries are important in describing interaction-induced phenomena in the excitation spectra of high $np$ Rydberg states. Long-range molecular resonances are such phenomena and they were first reported in S.M. Farooqi {\it et al.}, Phys. Rev. Lett. {\bf 91} 183002. One class of these resonances occurs at energies corresponding to excited atom pairs $(n-1)d+ns$. Such resonances are attributed to $\ell$-mixing due to Rydberg-Rydberg interactions so that otherwise forbidden molecular transitions become allowed. We calculate molecular potentials in Hund's case (c), use them to find the resonance lineshape and compare to experimental results.Comment: 11 pages, 7 figure

Scaling the neutral atom Rydberg gate quantum computer by collective encoding in Holmium atoms

We discuss a method for scaling a neutral atom Rydberg gate quantum processor to a large number of qubits. Limits are derived showing that the number of qubits that can be directly connected by entangling gates with errors at the $10^{-3}$ level using long range Rydberg interactions between sites in an optical lattice, without mechanical motion or swap chains, is about 500 in two dimensions and 7500 in three dimensions. A scaling factor of 60 at a smaller number of sites can be obtained using collective register encoding in the hyperfine ground states of the rare earth atom Holmium. We present a detailed analysis of operation of the 60 qubit register in Holmium. Combining a lattice of multi-qubit ensembles with collective encoding results in a feasible design for a 1000 qubit fully connected quantum processor.Comment: 6 figure

Millimeter wave satellite concepts. Volume 1: Executive summary

The objectives of the program were: (1) development of methodology based on the technical requirements of potential services that might be assigned to millimeter wave bands for identifying the viable and appropriate technologies for future NASA millimeter research and development programs, and (2) testing of this methodology with user applications and services. The scope of the program included the entire communications network, both ground and space subsystems. The reports include: (1) cost, weight, and performance models for the subsystems, (2) conceptual design for point-to-point and broadcast communications satellites, (3) analytic relationships between subsystem parameters and an overall link performance, (4) baseline conceptual systems, (5) sensitivity studies, (6) model adjustment analyses, (7) identification of critical technologies and their risks, (8) brief R&D program scenarios for the technologies judged to be moderate or extensive risks

Discovery of Recent Star Formation in the Extreme Outer Regions of Disk Galaxies

We present deep Halpha images of three nearby late-type spiral galaxies (NGC628, NGC1058 and NGC6946), which reveal the presence of HII regions out to, and beyond, two optical radii (defined by the 25th B-band isophote). The outermost HII regions appear small, faint and isolated, compared to their inner disk counterparts, and are distributed in organized spiral arm structures, likely associated with underlying HI arms and faint stellar arms. The relationship between the azimuthally--averaged Halpha surface brightness (proportional to star formation rate per unit area) and the total gas surface density is observed to steepen considerably at low gas surface densities. We find that this effect is largely driven by a sharp decrease in the covering factor of star formation at large radii, and not by changes in the rate at which stars form locally. An azimuthally--averaged analysis of the gravitational stability of the disk of NGC6946 reveals that while the existence of star formation in the extreme outer disk is consistent with the Toomre-Q instability model, the low rates observed are only compatible with the model when a constant gaseous velocity dispersion is assumed. We suggest that observed behaviour could also be explained by a model in which the star formation rate has an intrinsic dependence on the azimuthally-averaged gas volume density, which decreases rapidly in the outer disk due to the vertical flaring of the gas layer.Comment: 10 pages, 2 embedded postscript files, 3 jpeg images; accepted for publication in ApJ Letter

Optical conductivity of the half-filled Hubbard chain

We combine well-controlled analytical and numerical methods to determine the optical conductivity of the one-dimensional Mott-Hubbard insulator at zero temperature. A dynamical density-matrix renormalization group method provides the entire absorption spectrum for all but very small coupling strengths. In this limit we calculate the conductivity analytically using exact field-theoretical methods. Above the Lieb-Wu gap the conductivity exhibits a characteristic square-root increase. For small to moderate interactions, a sharp maximum occurs just above the gap. For larger interactions, another weak feature becomes visible around the middle of the absorption band.Comment: 4 pages with 3 eps figures, published version (changes in text and references

Imaging the evolution of an ultracold strontium Rydberg gas

Clouds of ultracold strontium 5s48s1S0 or 5s47d1D2 Rydberg atoms are created by two-photon excitation of laser-cooled 5s21S0 atoms. The spontaneous evolution of the cloud of low orbital angular momentum (low-ℓ) Rydberg states towards an ultracold neutral plasma is observed by imaging resonant light scattered from core ions, a technique that provides both spatial and temporal resolution. Evolution is observed to be faster for the S states, which display isotropic attractive interactions, than for the D states, which exhibit anisotropic, principally repulsive interactions. Immersion of the atoms in a dilute ultracold neutral plasma speeds up the evolution and allows the number of Rydberg atoms initially created to be determined

Electrocardiographic markers of structural heart disease and predictors of death in 2332 unselected patients undergoing outpatient Holter recording

To test the hypothesis that the QS interval of ventricular ectopic beats (VEBs) (ventricular ectopic QS interval, VEQSI) would provide a marker for the presence of structural heart disease and a predictor of mortality

Ionization of Rydberg atoms by blackbody radiation

We have studied an ionization of alkali-metal Rydberg atoms by blackbody radiation (BBR). The results of the theoretical calculations of ionization rates of Li, Na, K, Rb and Cs Rydberg atoms are presented. Calculations have been performed for nS, nP and nD states which are commonly used in a variety of experiments, at principal quantum numbers n=8-65 and at the three ambient temperatures of 77, 300 and 600 K. A peculiarity of our calculations is that we take into account the contributions of BBR-induced redistribution of population between Rydberg states prior to photoionization and field ionization by extraction electric field pulses. The obtained results show that these phenomena affect both the magnitude of measured ionization rates and shapes of their dependences on n. A Cooper minimum for BBR-induced transitions between bound Rydberg states of Li has been found. The calculated ionization rates are compared with our earlier measurements of BBR-induced ionization rates of Na nS and nD Rydberg states with n=8-20 at 300 K. A good agreement for all states except nS with n>15 is observed. Useful analytical formulas for quick estimation of BBR ionization rates of Rydberg atoms are presented. Application of BBR-induced ionization signal to measurements of collisional ionization rates is demonstrated.Comment: 36 pages, 16 figures. Paper is revised following NJP referees' comments and suggestion