Photoionization and Photoelectric Loading of Barium Ion Traps

Simple and effective techniques for loading barium ions into linear Paul traps are demonstrated. Two-step photoionization of neutral barium is achieved using a weak intercombination line (6s2 1S0 6s6p 3P1, 791 nm) followed by excitation above the ionization threshold using a nitrogen gas laser (337 nm). Isotopic selectivity is achieved by using a near Doppler-free geometry for excitation of the triplet 6s6p 3P1 state. Additionally, we report a particularly simple and efficient trap loading technique that employs an in-expensive UV epoxy curing lamp to generate photoelectrons.Comment: 5 pages, Accepted to PRA 3/20/2007 -fixed typo -clarified figure 3 caption -added reference [15

The CIV-MgII Kinematics Connection in <z>~0.7 Galaxies

We have examined Faint Object Spectrograph data from the Hubble Space Telescope Archive for CIV 1548,1550 absorption associated with 40 MgII 2796,2803 absorption-selected galaxies at 0.4 < z < 1.4. We report a strong correlation between MgII kinematics, measured in 6 km/s resolution HIRES/Keck spectra, and W_r(1548); this implies a physical connection between the processes that produce "outlying velocity" MgII clouds and high ionization galactic/halo gas. We found no trend in ionization condition, W_r(1548)/W_r(2796), with galaxy-QSO line-of-sight separation for 13 systems with confirmed associated galaxies, suggesting no obvious ionization gradient with galactocentric distance in these higher redshift galaxies. We find tentative evidence (2-sigma) that W_r(1548)/W_r(2796) is anti-correlated with galaxy color; if further data corroborate this trend, in view of the strong CIV-MgII kinematics correlation, it could imply a connection between stellar populations, star formation episodes, and the kinematics and ionization conditions of halo gas at z~1.Comment: Accepted to Astrophysical Journal Letters; 4 pages; 3 figures; emulateapj.st

Mg II Absorber Number Density at z~0.05: Implications for Omega_DLA Evolution

An unbiased sample of 147 quasar/AGN spectra, obtained with the FOS/HST, has been searched for intervening MgII absorbers over the redshift range 0<z<0.15. The total redshift path searched is 18.8, with the survey being 80% complete to a 5-sigma rest-frame equivalent width, W_r(2796), of 0.6 Ang. Main results of this work are: [1] Four systems were found, with a mean redshift of =0.06, yielding a redshift number density dN/dz=0.22(+0.12)(-0.09) for absorbers with W_r(2796)>0.6 Ang. This is consistent with the value expected if these systems do not evolve from higher redshifts (z=2.2). [2] No systems with W_r(2796)<0.6 Ang were found. It is a 2-sigma result to have a null detection of smaller W_r(2796) systems. If this implies a turnover in the low W_r(2796) region of the equivalent width distribution at z~0, then there is at least a 25% reduction in the average galaxy gas cross section from z<0.2 galaxies. [3] These systems have strong FeII absorption and are good candidates for damped Ly-alpha absorbers DLAs (see Rao & Turnshek 2000, ApJS, 130, 1). This translates to a redshift number density of dN/dz=0.08(+0.09)(-0.05) for DLAs at z~0. In tandem with the data analyzed by Rao & Turnshek, these results indicate that the redshift number density of DLAs does not evolve from z~4 to z~0. If the HI mass function does not evolve from z~0.5 to z~0, then the cosmological HI mass density is also deduced to not evolve from z~4 to z~0. These z~0 results for MgII absorption-selected DLAs are at odds with those based upon 21-cm emission from HI galaxies by a factor of five to six.Comment: 23 pages, 7 Figures, accepted to ApJ. Replaced version includes additional figures and tables and substantial modifications to the tex

"Hey, i'm having these experiences": Tumblr use and young people's queer (dis)connections

© 2019 Paul Byron, Brady Robards, Benjamin Hanckel, Son Vivienne, and Brendan Churchill. This article explores LGBTIQ+ young people's use of Tumblr-a social media platform often associated with queer youth cultures. Drawing on data from surveys (N = 1,304) and interviews (N = 23) with LGBTIQ+ young people in Australia, we argue that existing notions of "queer community" through digital media participation do not neatly align with young people's Tumblr practices. Our participants use Tumblr for connecting with others, yet these connections can be indirect, short term, and anonymous. Connections are often felt and practiced without directly communicating with other users, and many participants described their connections to the Tumblr platform itself as intense, pivotal to learning about genders and sexualities, and sometimes "toxic." We suggest that Tumblr use intensities reflect many young people's (dis)connections to queer life. Participant accounts of Tumblr use for identity, well-being, and (dis)connection practices can usefully inform health, education, and community workers engaging with LGBTIQ+ young people

The Population of Weak Mg II Absorbers I. A Survey of 26 QSO HIRES/Keck Spectra

We present a search for "weak" MgII absorbers [those with W_r(2796) < 0.3 A in the HIRES/Keck spectra of 26 QSOs. We found 30, of which 23 are newly discovered. The spectra are 80% complete to W_r(2796) = 0.02 A and have a cumulative redshift path of ~17.2 for the redshift range 0.4 < z < 1.4. The number of absorbers per unit redshift, dN/dz, is seen to increase as the equivalent width threshold is decreased; we obtained dN/dz = 1.74+/-0.10 for our 0.02 <= W_r(2796) < 0.3 A sample. The equivalent width distribution follows a power law with slope -1.0; there is no turnover down to W_r(2796) = 0.02 A at = 0.9. Weak absorbers comprise at least 65% of the total MgII absorption population, which outnumbers Lyman limit systems (LLS) by a factor of 3.8+/-1.1; the majority of weak MgII absorbers must arise in sub-LLS environments. Tentatively, we predict that ~5% of the Lyman-alpha forest clouds with W_r(1215) > 0.1 A will have detectable MgII absorption to W_r,min(2796) = 0.02 A and that this is primarily a high-metallicity selection effect (Z/Z_sun] > -1). This implies that MgII absorbing structures figure prominently as tracers of sub-LLS environments where gas has been processed by stars. We compare the number density of W_r(2796) > 0.02 A absorbers with that of both high and low surface brightness galaxies and find a fiducial absorber size of 35h^-1 to 63h^-1 kpc, depending upon the assumed galaxy population and their absorption properties. The individual absorbing "clouds" have W_r(2796) <= 0.15 A and their narrow (often unresolved) line widths imply temperatures of ~25,000 K. We measured W_r(1548) from CIV in FOS/HST archival spectra and, based upon comparisons with FeII, found a range of ionization conditions (low, high, and multi-phase) in absorbers selected by weak MgII.Comment: Accepted Version: 43 pages, PostScript figures embedded; accepted to ApJ; updated version includes analysis of CIV absorptio

The Physical Conditions of Intermediate Redshift MgII Absorbing Clouds from Voigt Profile Analysis

[Slightly Abridged] We present a detailed statistical analysis of the column densities, N, and Doppler parameters, b, of MgII absorbing clouds at redshifts 0.4<z<1.2. We use the HIRES/Keck data and Voigt profile (VP) fitting results presented by Churchill & Vogt (Paper I). The sample is comprised of 175 clouds from 23 systems along 18 quasar lines of sight. In order to understand whether inferred conditions could be "false", we performed extensive simulations of our VP analyses. In brief, we find: (1) N(FeII) and N(MgII) are correlated at the 9-sigma level. There is a 5-sigma anti-correlation between N(MgI)/N(MgII) and N(MgII). (2) Power-law fits to the distributions of N(MgII), N(FeII), and N(MgI) yielded power-law slopes of -1.6, -1.7, and -2.0. (3) The modes of the Doppler parameter distributions were ~5 km/s for MgII and FeII and ~7 km/s for MgI. The clouds are consistent with being thermally broadened, with temperatures in the 30-40,000K range. (4) A two-component Gaussian model to the velocity two-point correlation function yielded velocity dispersions of 54 km/s and 166 km/s. The narrow component has roughly twice the amplitude of the broader component. The width and amplitude of the broader component decreases as equivalent width increases. (5) From photoionization models we find that the column density ratios are most consistent with photoionization by the extragalactic background, as opposed to stars. Based upon N(MgI)/N(MgII), it appears that at least two-phase ionization models are required to explain the data.Comment: Accepted to the Astronomical Journal (January 2003

Non variability of intervening absorbers observed in the UVES spectra of the "naked-eye" GRB080319

The aim of this paper is to investigate the properties of the intervening absorbers lying along the line of sight of Gamma-Ray Burst (GRB) 080319B through the analysis of its optical absorption features. To this purpose, we analyze a multi-epoch, high resolution spectroscopic observations (R=40000, corresponding to 7.5 km/s) of the optical afterglow of GRB080319B (z=0.937), taken with UVES at the VLT. Thanks to the rapid response mode (RRM), we observed the afterglow just 8m:30s after the GRB onset when the magnitude was R ~ 12. This allowed us to obtain the best signal-to-noise, high resolution spectrum of a GRB afterglow ever (S/N per resolution element ~ 50). Two further RRM and target of opportunity observations were obtained starting 1.0 and 2.4 hours after the event, respectively. Four MgII absorption systems lying along the line of sight to the afterglow have been detected in the redshift range 0.5 < z < 0.8, most of them showing a complex structure featuring several components. Absorptions due to FeII, MgI and MnII are also present; they appear in four, two and one intervening absorbers, respectively. One out of four systems show a MgII2796 rest frame equivalent width larger than 1A. This confirms the excess of strong MgII absorbers compared to quasars, with dn/dz = 0.9, ~ 4 times larger than the one observed along quasar lines of sight. In addition, the analysis of multi-epoch, high-resolution spectra allowed us to exclude a significant variability in the column density of the single components of each absorber. Combining this result with estimates of the size of the emitting region, we can reject the hypothesis that the difference between GRB and QSO MgII absorbers is due to a different size of the emitting regions.Comment: 10 pages, 15 ps figures, submitted to MNRA

Dense sphere packings from optimized correlation functions

Elementary smooth functions (beyond contact) are employed to construct pair correlation functions that mimic jammed disordered sphere packings. Using the g2-invariant optimization method of Torquato and Stillinger [J. Phys. Chem. B 106, 8354, 2002], parameters in these functions are optimized under necessary realizability conditions to maximize the packing fraction phi and average number of contacts per sphere Z. A pair correlation function that incorporates the salient features of a disordered packing and that is smooth beyond contact is shown to permit a phi of 0.6850: this value represents a 45% reduction in the difference between the maximum for congruent hard spheres in three dimensions, pi/sqrt{18} ~ 0.7405, and 0.64, the approximate fraction associated with maximally random jammed (MRJ) packings in three dimensions. We show that, surprisingly, the continued addition of elementary functions consisting of smooth sinusoids decaying as r^{-4} permits packing fractions approaching pi/sqrt{18}. A translational order metric is used to discriminate between degrees of order in the packings presented. We find that to achieve higher packing fractions, the degree of order must increase, which is consistent with the results of a previous study [Torquato et al., Phys. Rev. Lett. 84, 2064, 2000].Comment: 26 pages, 9 figures, 1 table; added references, fixed typos, simplified argument and discussion in Section IV

Demonstration of Entanglement of Electrostatically Coupled Singlet-Triplet Qubits

Quantum computers have the potential to solve certain interesting problems significantly faster than classical computers. To exploit the power of a quantum computation it is necessary to perform inter-qubit operations and generate entangled states. Spin qubits are a promising candidate for implementing a quantum processor due to their potential for scalability and miniaturization. However, their weak interactions with the environment, which leads to their long coherence times, makes inter-qubit operations challenging. We perform a controlled two-qubit operation between singlet-triplet qubits using a dynamically decoupled sequence that maintains the two-qubit coupling while decoupling each qubit from its fluctuating environment. Using state tomography we measure the full density matrix of the system and determine the concurrence and the fidelity of the generated state, providing proof of entanglement