Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks

We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method -- a single clock laser combined with a DC magnetic field-- relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10^-17 for the metrologically preferred even isotopes

Direct excitation of the forbidden clock transition in neutral 174Yb atoms confined to an optical lattice

We report direct single-laser excitation of the strictly forbidden (6s^2)^1S_0 -(6s6p)^3P_0 clock transition in the even 174Yb isotope confined to a 1D optical lattice. A small (~1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FHWM) with high contrast were observed, demonstrating a record neutral-atom resonance quality factor of 2.6x10^13. The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35+/-0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks, and can create new clock possibilities in other alkaline earth-like atoms such as Mg and Ca.Comment: Submitted to Physics Review Letter

Structural disjoining potential for grain boundary premelting and grain coalescence from molecular-dynamics simulations

We describe a molecular dynamics framework for the direct calculation of the short-ranged structural forces underlying grain-boundary premelting and grain-coalescence in solidification. The method is applied in a comparative study of (i) a Sigma 9 120 degress twist and (ii) a Sigma 9 {411} symmetric tilt boundary in a classical embedded-atom model of elemental Ni. Although both boundaries feature highly disordered structures near the melting point, the nature of the temperature dependence of the width of the disordered regions in these boundaries is qualitatively different. The former boundary displays behavior consistent with a logarithmically diverging premelted layer thickness as the melting temperature is approached from below, while the latter displays behavior featuring a finite grain-boundary width at the melting point. It is demonstrated that both types of behavior can be quantitatively described within a sharp-interface thermodynamic formalism involving a width-dependent interfacial free energy, referred to as the disjoining potential. The disjoining potential for boundary (i) is calculated to display a monotonic exponential dependence on width, while that of boundary (ii) features a weak attractive minimum. The results of this work are discussed in relation to recent simulation and theoretical studies of the thermodynamic forces underlying grain-boundary premelting.Comment: 24 pages, 8 figures, 1 tabl

Optical Lattice Induced Light Shifts in an Yb Atomic Clock

We present an experimental study of the lattice induced light shifts on the 1S_0-3P_0 optical clock transition (v_clock~518 THz) in neutral ytterbium. The ``magic'' frequency, v_magic, for the 174Yb isotope was determined to be 394 799 475(35)MHz, which leads to a first order light shift uncertainty of 0.38 Hz on the 518 THz clock transition. Also investigated were the hyperpolarizability shifts due to the nearby 6s6p 3P_0 - 6s8p 3P_0, 6s8p 3P_2, and 6s5f 3F_2 two-photon resonances at 759.708 nm, 754.23 nm, and 764.95 nm respectively. By tuning the lattice frequency over the two-photon resonances and measuring the corresponding clock transition shifts, the hyperpolarizability shift was estimated to be 170(33) mHz for a linear polarized, 50 uK deep, lattice at the magic wavelength. In addition, we have confirmed that a circularly polarized lattice eliminates the J=0 - J=0 two-photon resonance. These results indicate that the differential polarizability and hyperpolarizability frequency shift uncertainties in a Yb lattice clock could be held to well below 10^-17.Comment: Accepted to PR

Observation and absolute frequency measurements of the 1S0 - 3P0 optical clock transition in ytterbium

We report the direct excitation of the highly forbidden (6s^2) 1S0 - (6s6p) 3P0 optical transition in two odd isotopes of ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at ~70 uK in a magneto-optical trap. The measured frequency in 171Yb (F=1/2) is 518,295,836,593.2 +/- 4.4 kHz. The measured frequency in 173Yb (F=5/2) is 518,294,576,850.0 +/- 4.4 kHz. Measurements are made with a femtosecond-laser frequency comb calibrated by the NIST cesium fountain clock and represent nearly a million-fold reduction in uncertainty. The natural linewidth of these J=0 to J=0 transitions is calculated to be ~10 mHz, making them well-suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.Comment: 4 pages, 3 figure

Paramagnetic reentrant effect in high purity mesoscopic AgNb proximity structures

We discuss the magnetic response of clean Ag coated Nb proximity cylinders in the temperature range 150 \mu K < T < 9 K. In the mesoscopic temperature regime, the normal metal-superconductor system shows the yet unexplained paramagnetic reentrant effect, discovered some years ago [P. Visani, A. C. Mota, and A. Pollini, Phys. Rev. Lett. 65, 1514 (1990)], superimposing on full Meissner screening. The logarithmic slope of the reentrant paramagnetic susceptibility chi_para(T) \propto \exp(-L/\xi_N) is limited by the condition \xi_N=n L, with \xi_N=\hbar v_F/2 \pi k_B T, the thermal coherence length and n=1,2,4. In wires with perimeters L=72 \mu m and L=130 \mu m, we observe integer multiples n=1,2,4. At the lowest temperatures, \chi_para compensates the diamagnetic susceptibility of the \textit{whole} AgNb structure.Comment: 4 pages, 4 figures (color

Mental and substance use disorders from early adolescence to young adulthood among indigenous young people: final diagnostic results from an 8-year panel study

Objective—Our objective was to investigate change in prevalence rates for mental and substance abuse disorders between early adolescence and young adulthood in a cohort of indigenous adolescents who participated in an 8-year panel study. Method—The data are from a lagged, sequential study of 671 indigenous adolescents (Wave 1) from a single culture in the Northern Midwest USA and Canada. At Wave 1 (mean age 11.3 years, Wave 4 (mean age 14.3 years), Wave 6 (mean age 16.2 years), and at Wave 8 (mean age 18.3 years) the tribally enrolled adolescents completed a computer-assisted personal interview that included DISC-R assessment for 11 diagnoses. Our yearly retention rates by diagnostic wave were: Wave 2, 94.7 %; Wave 4, 87.7 %; Wave 6, 88.0 %; Wave 8, 78.5 %. Results—The findings show a dramatic increase in lifetime prevalence rates for substance use disorders. By young adulthood, over half had met criteria of substance abuse or dependence disorder. Also at young adulthood, 58.2 % had met lifetime criteria of a single substance use or mental disorder and 37.2 % for two or more substance use or mental disorders. The results are compared to other indigenous diagnostic studies and to the general population. Conclusions—A mental health crisis exists within the indigenous populations that participated in this study. Innovations within current mental health service systems are needed to address the unmet demand of adolescents and families

Mental and substance use disorders from early adolescence to young adulthood among indigenous young people: final diagnostic results from an 8-year panel study

Objective—Our objective was to investigate change in prevalence rates for mental and substance abuse disorders between early adolescence and young adulthood in a cohort of indigenous adolescents who participated in an 8-year panel study. Method—The data are from a lagged, sequential study of 671 indigenous adolescents (Wave 1) from a single culture in the Northern Midwest USA and Canada. At Wave 1 (mean age 11.3 years, Wave 4 (mean age 14.3 years), Wave 6 (mean age 16.2 years), and at Wave 8 (mean age 18.3 years) the tribally enrolled adolescents completed a computer-assisted personal interview that included DISC-R assessment for 11 diagnoses. Our yearly retention rates by diagnostic wave were: Wave 2, 94.7 %; Wave 4, 87.7 %; Wave 6, 88.0 %; Wave 8, 78.5 %. Results—The findings show a dramatic increase in lifetime prevalence rates for substance use disorders. By young adulthood, over half had met criteria of substance abuse or dependence disorder. Also at young adulthood, 58.2 % had met lifetime criteria of a single substance use or mental disorder and 37.2 % for two or more substance use or mental disorders. The results are compared to other indigenous diagnostic studies and to the general population. Conclusions—A mental health crisis exists within the indigenous populations that participated in this study. Innovations within current mental health service systems are needed to address the unmet demand of adolescents and families

Genetically engineered pigs and target-specific immunomodulation provide significant graft survival and hope for clinical cardiac xenotransplantation

ObjectivesCardiac transplantation and available mechanical alternatives are the only possible solutions for end-stage cardiac disease. Unfortunately, because of the limited supply of human organs, xenotransplantation may be the ideal method to overcome this shortage. We have recently seen significant prolongation of heterotopic cardiac xenograft survival from 3 to 12 months and beyond.MethodsHearts from genetically engineered piglets that were alpha 1-3 galactosidase transferase knockout and expressed the human complement regulatory gene, CD46 (groups A-C), and the human thrombomodulin gene (group D) were heterotropically transplanted in baboons treated with antithymocyte globulin, cobra venom factor, anti-CD20 antibody, and costimulation blockade (anti-CD154 antibody [clone 5C8]) in group A, anti-CD40 antibody (clone 3A8; 20 mg/kg) in group B, clone 2C10R4 (25 mg/kg) in group C, or clone 2C10R4 (50 mg/kg) in group D, along with conventional nonspecific immunosuppressive agents.ResultsGroup A grafts (n = 8) survived for an average of 70 days, with the longest survival of 236 days. Some animals in this group (n = 3) developed microvascular thrombosis due to platelet activation and consumption, which resulted in spontaneous hemorrhage. The median survival time was 21 days in group B (n = 3), 80 days in group C (n = 6), and more than 200 days in group D (n = 5). Three grafts in group D are still contracting well, with the longest ongoing graft survival surpassing the 1-year mark.ConclusionsGenetically engineered pig hearts (GTKOhTg.hCD46.hTBM) with modified targeted immunosuppression (anti-CD40 monoclonal antibody) achieved long-term cardiac xenograft survival. This potentially paves the way for clinical xenotransplantation if similar survival can be reproduced in an orthotopic transplantation model