Increasing efficiency of a linear-optical quantum gate using an electronic feed forward

We have successfully used a fast electronic feed forward to increase the success probability of a linear optical implementation of a programmable phase gate from 25% to its theoretical limit of 50%. The feed forward applies a conditional unitary operation which changes the incorrect output states of the data qubit to the correct ones. The gate itself rotates an arbitrary quantum state of the data qubit around the z-axis of the Bloch sphere with the angle of rotation being fully determined by the state of the program qubit. The gate implementation is based on fiber optics components. Qubits are encoded into spatial modes of single photons. The signal from the feed-forward detector is led directly to a phase modulator using only a passive voltage divider. We have verified the increase of the success probability and characterized the gate operation by means of quantum process tomography. We have demonstrated that the use of the feed forward does not affect either the process fidelity or the output-state fidelities

Magellan LDSS3 emission confirmation of galaxies hosting metal-rich Lyman-alpha absorption systems

Using the Low Dispersion Survey Spectrograph 3 at the Magellan II Clay Telescope, we target {candidate absorption host galaxies} detected in deep optical imaging {(reaching limiting apparent magnitudes of 23.0-26.5 in $g, r, i,$ and $z$ filters) in the fields of three QSOs, each of which shows the presence of high metallicity, high $N_{\rm HI}$ absorption systems in their spectra (Q0826-2230: $z_{abs}$=0.9110, Q1323-0021: $z_{abs}=0.7160$, Q1436-0051: $z_{abs}=0.7377, 0.9281$). We confirm three host galaxies {at redshifts 0.7387, 0.7401, and 0.9286} for two of the Lyman-$\alpha$ absorption systems (one with two galaxies interacting). For these systems, we are able to determine the star formation rates (SFRs); impact parameters (from previous imaging detections); the velocity shift between the absorption and emission redshifts; and, for one system, also the emission metallicity.} Based on previous photometry, we find these galaxies have L$>$L$^{\ast}$. The [O II] SFRs for these galaxies are in the range $11-25$ M$_{\odot}$ yr$^{-1}$ {(uncorrected for dust)}, while the impact parameters lie in the range $35-54$ kpc. {Despite the fact that we have confirmed galaxies at 50 kpc from the QSO, no gradient in metallicity is indicated between the absorption metallicity along the QSO line of sight and the emission line metallicity in the galaxies.} We confirm the anti-correlation between impact parameter and $N_{\rm HI}$ from the literature. We also report the emission redshift of five other galaxies: three at $z_{em}>z_{QSO}$, and two (L$<$L$^{\ast}$) at $z_{em}<z_{QSO}$ not corresponding to any known absorption systems.Comment: 14 pages, 7 figures, 4 tables, accepted to MNRA

Asteroseismology across the HR diagram

High precision spectroscopy provides essential information necessary to fully exploit the opportunity of probing the internal structure of stars using Asteroseismology. In this work we discuss how Asteroseismology combined with High Precision Spectroscopy can establish a detailed view on stellar structure and evolution of stars across the HR diagramme.Comment: 6 pages, 2 figures - to appear in Precision Spectroscopy in Astrophysics, (Eds) L. Pasquini, M. Romaniello, N.C. Santos, and A. Correia, ESO Astrophysics Symposia, 200

Plumo: An Ultralight Blockchain Client

Syncing the latest state of a blockchain can be a resource-intensive task, driving (especially mobile) end users towards centralized services offering instant access. To expand full decentralized access to anyone with a mobile phone, we introduce a consensus-agnostic compiler for constructing ultralight clients, providing secure and highly efficient blockchain syncing via a sequence of SNARK-based state transition proofs, and prove its security formally. Instantiating this, we present Plumo, an ultralight client for the Celo blockchain capable of syncing the latest network state summary in just a few seconds even on a low-end mobile phone. In Plumo, each transition proof covers four months of blockchain history and can be produced for just $25 USD of compute. Plumo achieves this level of efficiency thanks to two new SNARK-friendly constructions, which may also be of independent interest: a new BLS-based offline aggregate multisignature scheme in which signers do not have to know the members of their multisignature group in advance, and a new composite algebraic-symmetric cryptographic hash function

Damped Ly-alpha Absorbers in Star-forming Galaxies at z < 0.15 Detected with the Hubble Space Telescope and Implications for Galaxy Evolution

We report {\it HST} COS spectroscopy of 10 quasars with foreground star-forming galaxies at 0.02$<$$z$$<$ 0.14 within impact parameters of $\sim$1-7 kpc. We detect damped/sub-damped Ly$\alpha$ absorption in 100$\%$ of cases where no higher-redshift Lyman-limit systems extinguish the flux at the expected wavelength of Ly$\alpha$ absorption, obtaining the largest targeted sample of DLA/sub-DLAs in low-redshift galaxies. We present absorption measurements of neutral hydrogen and metals. Additionally, we present GBT 21-cm emission measurements for 5 of the galaxies (including 2 detections). Combining our sample with the literature, we construct a sample of 115 galaxies associated with DLA/sub-DLAs spanning 0$<$$z$$<$4.4, and examine trends between gas and stellar properties, and with redshift. The H~I column density is anti-correlated with impact parameter and stellar mass. More massive galaxies appear to have gas-rich regions out to larger distances. The specific SFR (sSFR) of absorbing galaxies increases with redshift and decreases with $M^{\ast}$, consistent with evolution of the star-formation main sequence (SFMS). However, $\sim$20$\%$ of absorbing galaxies lie below the SFMS, indicating that some DLA/sub-DLAs trace galaxies with longer-than-typical gas-depletion time-scales. Most DLA/sub-DLA galaxies with 21-cm emission have higher H I masses than typical galaxies with comparable $M^{\ast}$. High $M_{\rm H I}/M^{\ast}$ ratios and high sSFRs in DLA/sub-DLA galaxies with $M^{\ast}$$<$$10^{9}$$M_{\odot}$ suggest these galaxies may be gas-rich because of recent gas accretion rather than inefficient star formation. Our study demonstrates the power of absorption and emission studies of DLA/sub-DLA galaxies for extending galaxy-evolution studies to previously under-explored regimes of low $M^{\ast}$ and low SFR.Comment: 51 pages, 12 figures. Submitted to the Astrophysical Journa

YREC: The Yale Rotating Stellar Evolution Code

The stellar evolution code YREC is outlined with emphasis on its applications to helio- and asteroseismology. The procedure for calculating calibrated solar and stellar models is described. Other features of the code such as a non-local treatment of convective core overshoot, and the implementation of a parametrized description of turbulence in stellar models, are considered in some detail. The code has been extensively used for other astrophysical applications, some of which are briefly mentioned at the end of the paper.Comment: 10 pages, 2 figures, ApSS accepte

Ubiquitous giant Ly α\alpha nebulae around the brightest quasars at z∼3.5z\sim3.5 revealed with MUSE

Direct Ly $\alpha$ imaging of intergalactic gas at $z\sim2$ has recently revealed giant cosmological structures around quasars, e.g. the Slug Nebula (Cantalupo et al. 2014). Despite their high luminosity, the detection rate of such systems in narrow-band and spectroscopic surveys is less than 10%, possibly encoding crucial information on the distribution of gas around quasars and the quasar emission properties. In this study, we use the MUSE integral-field instrument to perform a blind survey for giant Ly $\alpha$ nebulae around 17 bright radio-quiet quasars at $3<z<4$ that does not suffer from most of the limitations of previous surveys. After data reduction and analysis performed with specifically developed tools, we found that each quasar is surrounded by giant Ly $\alpha$ nebulae with projected sizes larger than 100 physical kpc and, in some cases, extending up to 320 kpc. The circularly averaged surface brightness profiles of the nebulae appear very similar to each other despite their different morphologies and are consistent with power laws with slopes $\approx-1.8$. The similarity between the properties of all these nebulae and the Slug Nebula suggests a similar origin for all systems and that a large fraction of gas around bright quasars could be in a relatively "cold" (T$\sim$10$^4$K) and dense phase. In addition, our results imply that such gas is ubiquitous within at least 50 kpc from bright quasars at $3<z<4$ independently of the quasar emission opening angle, or extending up to 200 kpc for quasar isotropic emission.Comment: 19 pages, 9 figures, 3 Tables, accepted to Ap

Coexistence of ferro- and antiferromagnetic order in Mn-doped Ni2_2MnGa

Ni-Mn-Ga is interesting as a prototype of a magnetic shape-memory alloy showing large magnetic field induced strains. We present here results for the magnetic ordering of Mn-rich Ni-Mn-Ga alloys based on both experiments and theory. Experimental trends for the composition dependence of the magnetization are measured by a vibrating sample magnetometer (VSM) in magnetic fields of up to several tesla and at low temperatures. The saturation magnetization has a maximum near the stoichiometric composition and it decreases with increasing Mn content. This unexpected behaviour is interpreted via first-principles calculations within the density-functional theory. We show that extra Mn atoms are antiferromagnetically aligned to the other moments, which explains the dependence of the magnetization on composition. In addition, the effect of Mn doping on the stabilization of the structural phases and on the magnetic anisotropy energy is demonstrated.Comment: 4 pages, 3 figure

Current Issues in Asteroseismology

In this contribution we briefly review some of the current issues and promises for the future by asteroseismology. We are entering a new phase in this field driven by the wealth of data that has been collected and data that will soon be available for asteroseismology across the HR Diagram. Major difficulties in the descriptions of stellar interiors that arose in the second half of the 20th century may now be in part addressed and solved (this is the expectation!) by asteroseismology with unprecedented precision. In this contribution we list some of the key open questions in stellar physics, the seismic data we expect to collect in the near future, and some techniques that will provide the tools to connect data and models.Comment: 9 pages, 2 figures - to appear in Helioseismology, Asteroseismology and MHD Connections, (Eds) L. Gizon et al., Journal of Physics Conference Series, 2008 [Revision 1 - english; Revision 2 - references