Photon Echoes Produced by Switching Electric Fields

We demonstrate photon echoes in Eu$^{3+}$:Y$_{2}$SiO$_{5}$ by controlling the inhomogeneous broadening of the Eu$^{3+}$ $^{7}$F$_{0}\leftrightarrow^{5}$D$_{0}$ optical transition. This transition has a linear Stark shift and we induce inhomogeneous broadening by applying an external electric field gradient. After optical excitation, reversing the polarity of the field rephases the ensemble, resulting in a photon echo. This is the first demonstration of such a photon echo and its application as a quantum memory is discussed.Comment: improved introduction, including theoretical outline of the relvant quantum memory proposa

Method of extending hyperfine coherence times in Pr^3+:Y_2SiO_5

In this letter we present a method for increasing the coherence time of praseodymium hyperfine ground state transitions in Pr^3+:Y_2SiO_5 by the application of a specific external magnetic field. The magnitude and angle of the external field is applied such that the Zeeman splitting of a hyperfine transition is at a critical point in three dimensions, making the first order Zeeman shift vanishingly small for the transition. This reduces the influence of the magnetic interactions between the praseodymium ions and the spins in the host lattice on the transition frequency. Using this method a phase memory time of 82ms was observed, a value two orders of magnitude greater than previously reported. It is shown that the residual dephasing is amenable quantum error correction

High titers of transmissible spongiform encephalopathy infectivity associated with extremely low levels of PrP in vivo

Rona Barron - ORCID: 0000-0003-4512-9177 https://orcid.org/0000-0003-4512-9177Diagnosis of transmissible spongiform encephalopathy (TSE) disease in humans and ruminants relies on the detection in post-mortem brain tissue of the protease-resistant form of the host glycoprotein PrP. The presence of this abnormal isoform (PrPSc) in tissues is taken as indicative of the presence of TSE infectivity. Here we demonstrate conclusively that high titers of TSE infectivity can be present in brain tissue of animals that show clinical and vacuolar signs of TSE disease but contain low or undetectable levels of PrPSc. This work questions the correlation between PrPSc level and the titer of infectivity and shows that tissues containing little or no proteinase K-resistant PrP can be infectious and harbor high titers of TSE infectivity. Reliance on protease-resistant PrPSc as a sole measure of infectivity may therefore in some instances significantly underestimate biological properties of diagnostic samples, thereby undermining efforts to contain and eradicate TSEs.https://doi.org/10.1074/jbc.M704329200282pubpub4

Relationship between adiposity and admixture in African-American and Hispanic-American women.

ObjectiveThe objective of this study was to investigate whether differences in admixture in African-American (AFA) and Hispanic-American (HA) adult women are associated with adiposity and adipose distribution.DesignThe proportion of European, sub-Saharan African and Amerindian admixture was estimated for AFA and HA women in the Women's Heath Initiative using 92 ancestry informative markers. Analyses assessed the relationship between admixture and adiposity indices.SubjectsThe subjects included 11 712 AFA and 5088 HA self-identified post-menopausal women.ResultsThere was a significant positive association between body mass index (BMI) and African admixture when BMI was considered as a continuous variable, and age, education, physical activity, parity, family income and smoking were included covariates (P<10(-4)). A dichotomous model (upper and lower BMI quartiles) showed that African admixture was associated with a high odds ratio (OR=3.27 (for 100% admixture compared with 0% admixture), 95% confidence interval 2.08-5.15). For HA, there was no association between BMI and admixture. In contrast, when waist-to-hip ratio (WHR) was used as a measure of adipose distribution, there was no significant association between WHR and admixture in AFA but there was a strong association in HA (P<10(-4); OR Amerindian admixture=5.93, confidence interval=3.52-9.97).ConclusionThese studies show that: (1) African admixture is associated with BMI in AFA women; (2) Amerindian admixture is associated with WHR but not BMI in HA women; and (3) it may be important to consider different measurements of adiposity and adipose distribution in different ethnic population groups

Empirical wind model for the middle and lower atmosphere. Part 1: Local time average

The HWM90 thermospheric wind model was revised in the lower thermosphere and extended into the mesosphere and lower atmosphere to provide a single analytic model for calculating zonal and meridional wind profiles representative of the climatological average for various geophysical conditions. Gradient winds from CIRA-86 plus rocket soundings, incoherent scatter radar, MF radar, and meteor radar provide the data base and are supplemented by previous data driven model summaries. Low-order spherical harmonics and Fourier series are used to describe the major variations throughout the atmosphere including latitude, annual, semiannual, and longitude (stationary wave 1). The model represents a smoothed compromise between the data sources. Although agreement between various data sources is generally good, some systematic differences are noted, particularly near the mesopause. Root mean square differences between data and model are on the order of 15 m/s in the mesosphere and 10 m/s in the stratosphere for zonal wind, and 10 m/s and 4 m/s, respectively, for meridional wind

Assignment of the NV0 575 nm zero-phonon line in diamond to a 2E-2A2 transition

The time-averaged emission spectrum of single nitrogen-vacancy defects in diamond gives zero-phonon lines of both the negative charge state at 637 nm (1.945 eV) and the neutral charge state at 575 nm (2.156 eV). This occurs through photo-conversion between the two charge states. Due to strain in the diamond the zero-phonon lines are split and it is found that the splitting and polarization of the two zero-phonon lines are the same. From this observation and consideration of the electronic structure of the nitrogen-vacancy center it is concluded that the excited state of the neutral center has A2 orbital symmetry. The assignment of the 575 nm transition to a 2E - 2A2 transition has not been established previously.Comment: 5 pages, 5 figure

Magnetic properties of the quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6

We report on high-field magnetization, specific-heat and electron spin resonance (ESR) studies of the quasi-two-dimensional spin-1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6. The frequency-field diagram of ESR modes below TN = 4.38 K is described in the frame of the meanfield theory, confirming a collinear magnetic structure with an easy-plane anisotropy. The obtained results allowed us to determine the anisotropy/exchange interaction ratio, A/J = 0.003, and the upper limit for the inter/intra-plane exchange-interaction ratio, J'/J = 1/16. It is argued that despite the onset of 3D long-range magnetic ordering the magnetic properties of this material (including high-magnetic-field magnetization and non-monotonic field dependence of the Neel temperature) are strongly affected by two-dimensional spin correlations.Comment: 5 pages, 7 figure