Lick Slit Spectra of Thirty-Eight Objective Prism QSO Candidates and Low Metallicity Halo Stars

We present Lick Observatory slit spectra of 38 objects which were claimed to have pronounced ultraviolet excess and emission lines by Zhan \& Chen. Most of our spectra have FWHM spectral resolutions of about 4~\AA , and relatively high S/N of about 10 -- 50, although some have FWHM $\simeq 15$~\AA ~or lower S/N. We find eleven QSOs, four galaxies at $z \simeq 0.1$, twenty-two stars and one unidentified object with a low S/N spectrum. Six of the QSOs show absorption systems, including Q0000+027A with a relatively strong associated C~IV absorption system, and Q0008+008 (V$\simeq 18.9$) with a damped Ly$\alpha$ system with an H~I column density of $10^{21}$ cm$^{-2}$. The stars include a wide variety of spectral types. There is one new DA4 white dwarf at 170~pc, one sdB at 14~kpc, and three M stars. The rest are of types F, G and K. We have measured the equivalent widths of the Ca~II~K line, the G-band and the Balmer lines in ten stars with the best spectra, and we derive metallicities. Seven of them are in the range $-2.5 \leq$~[Fe/H]~$\leq -1.7$, while the others are less metal poor. If the stars are dwarfs, then they are at distances of 1 to 7~kpc, but if they are giants, typical distances will be about 10~kpc.Comment: (Plain Tex, 21 pages, including tables. Send email to 'travell_oir%[email protected]' for 12 pages of figures) To appear in the %%Astronomical Journal, August, 199

Theory of control of spin/photon interface for quantum networks

A cavity coupling a charged nanodot and a fiber can act as a quantum interface, through which a stationary spin qubit and a flying photon qubit can be inter-converted via cavity-assisted Raman process. This Raman process can be controlled to generate or annihilate an arbitrarily shaped single-photon wavepacket by pulse-shaping the controlling laser field. This quantum interface forms the basis for many essential functions of a quantum network, including sending, receiving, transferring, swapping, and entangling qubits at distributed quantum nodes as well as a deterministic source and an efficient detector of a single photon wavepacket with arbitrarily specified shape and average photon number. Numerical study of noise effects on the operations shows high fidelity.Comment: 4 pages, 2 figure

Lick Optical Spectra of Quasar HS 1946+7658 at 10 km/sec Resolution: Lyman-Alpha Forest and Metal Absorption Systems

We present optical spectra of QSO HS~1946+7658 with either high resolution (FWHM=10 km/s) or high signal to noise ratio (SNR=40-100). We find 113 Lyman alpha and six metal line systems. The metal systems at Zabs=2.844 and 3.050 have complex velocity structures. We find that the system at 2.844 is a damped Ly-a absorption system, with neutral hydrogen column density of logN(HI)=20.2+/-0.4, and it is the cause of the Lyman limit break at 3520\AA. The metal abundance in the gas phase of the system is [M/H]=-2.6+/-0.3, with a best estimate of [M/H]= -2.8, with ionization parameter Gamma=-2.75, from a photoionization model. We show that the abundance ratios rule out appreciable dust in this DLA system. We do not see the enhancement of O over C reported in Nature by Reimers last years. We see CII*(1335) offset by 15 km/s with respect to CII(1334), presumably because the gas density varies from 2 - 8 cm(-3) with changing velocity in the DLA system. These densities imply that the damped component is 6 - 25 pc thick, which is reasonable for a single cloud in a cold spiral disk. We see a 2.6sigma lack of Ly-a forest lines well away from the QSO redshift, which may be a chance fluctuation. We also see a correlation between column density N(HI) and Doppler parameter b for 96 unsaturated Ly-a forest absorption lines, and although this correlation persists in the 36 Ly-a lines which lie in regions where SNR=8-16, we agree with Rauch etal (1993) that it is probably a bogus effect of low SNR. We show that there are few low-b Ly-a forest lines in moderate SNR data.Comment: (Plain Tex, 46 pages and 21 figures. To get 21 postscript files for figures ftp to 132.239.146.152 and login as ftp in directory /pub/fan). To appear in the Astrophysical Journal Supplement