Persistent control of a superconducting qubit by stroboscopic measurement feedback

Making a system state follow a prescribed trajectory despite fluctuations and errors commonly consists in monitoring an observable (temperature, blood-glucose level...) and reacting on its controllers (heater power, insulin amount ...). In the quantum domain, there is a change of paradigm in feedback since measurements modify the state of the system, most dramatically when the trajectory goes through superpositions of measurement eigenstates. Here, we demonstrate the stabilization of an arbitrary trajectory of a superconducting qubit by measurement based feedback. The protocol benefits from the long coherence time ($T_2>10 \mu$s) of the 3D transmon qubit, the high efficiency (82%) of the phase preserving Josephson amplifier, and fast electronics ensuring less than 500 ns delay. At discrete time intervals, the state of the qubit is measured and corrected in case an error is detected. For Rabi oscillations, where the discrete measurements occur when the qubit is supposed to be in the measurement pointer states, we demonstrate an average fidelity of 85% to the targeted trajectory. For Ramsey oscillations, which does not go through pointer states, the average fidelity reaches 75%. Incidentally, we demonstrate a fast reset protocol allowing to cool a 3D transmon qubit down to 0.6% in the excited state.Comment: 7 pages, 3 figures and 1 table. Supplementary information available as an ancilla fil

TABARNAC: Tools for Analyzing Behavior of Applications Running on NUMA Architecture

In modern parallel architectures, memory accesses represent a commonbottleneck. Thus, optimizing the way applications access the memory is an important way to improve performance and energy consumption. Memory accesses are even more important with NUMAmachines, as the access time to data depends on its location inthe memory. Many efforts were made todevelop adaptive tools to improve memory accesses at the runtime by optimizingthe mapping of data and threads to NUMA nodes. However, theses tools are notable to change the memory access pattern of the original application,therefore a code written without considering memory performance mightnot benefit from them. Moreover, automatic mapping tools take time to convergetowards the best mapping, losing optimization opportunities. Adeeper understanding of the memory behavior can help optimizing it,removing the need for runtime analysis.In this paper, we present TABARNAC, a tool for analyzing the memory behavior of parallel applications with a focus on NUMA architectures.TABARNAC provides a new visualization of the memory access behavior, focusing on thedistribution of accesses by thread and by structure. Such visualization allows thedeveloper to easily understand why performance issues occur and how to fix them.Using TABARNAC, we explain why some applications do not benefit from dataand thread mapping. Moreover, we propose several code modifications toimprove the memory access behavior of several parallel applications.Les accès mémoire représentent une source de problème de performance fréquenteavec les architectures parallèle moderne. Ainsi optimiser la manière dont lesapplications accèdent à la mémoire est un moyen efficace d'améliorer laperformance et la consommation d'énergie. Les accès mémoire prennent d'autantplus d'important avec les machines NUMA où le temps d'accès à une donnéedépend de sa localisation dans la mémoire. De nombreuse études ont proposéesdes outils adaptatif pour améliorer les accès mémoire en temps réel, cesoutils opèrent en changeant le placement des données et des thread sur lesnœuds NUMA. Cependant ces outils n'ont pas la possibilité de changer la façondont l'application accède à la mémoire. De ce fait un code développé sansprendre en compte les performances des accès mémoire pourrait ne pas en tirerparti. De plus les outils de placement automatique ont besoin de temps pourconverger vers le meilleur placement, perdant des opportunités d'optimisation.Mieux comprendre le comportement mémoire peut aider à l'optimiser et supprimerle besoin d'optimisation en temps réel.Cette étude présente TABARNAC un outil pour analyser le comportement mémoired'application parallèles s'exécutant sur architecture NUMA. TABARNAC offreune nouvelle forme de visualisation du comportement mémoire mettant l'accentsur la distribution des accès entre les thread et par structure de données. Cetype de visualisations permettent de comprendre facilement pourquoi lesproblèmes de performances apparaissent et comment les résoudre. En utilisantTABARNAC, nous expliquons pourquoi certaines applications ne tirent pas partid'outils placement de donnée et de thread. De plus nous proposons plusieursmodification de code permettant d'améliorer le comportement mémoire de plusieursapplications parallèles

Moca: Un système efficient de collecte de traces mémoire

In modern High Performance Computing architectures, the memory subsystem is a common performance bottleneck. When optimizing an application, the developer has to study its memory access patterns and adapt accordingly the algorithms and data structures it uses. The objective is twofold: on one hand, it is necessary to avoid missuses of the memory hierarchy such as false sharing of cache lines or contention in a NUMA interconnect. On the other hand, it is essential to take advantage of the various cache levels and the memory hardware prefetcher. Still, most profiling tools focus on CPU metrics. The few of them able to provide an overview of the memory patterns involved by the execution rely on hardware instrumentation mechanisms and have two drawbacks. The first one is that they are based on sampling which precision is limited by hardware capabilities. The second one is that they trace a subset of all the memory accesses, usually the most frequent, without information about the other ones. In this study we present Moca an efficient tool for the collection of complete spatiotemporal memory traces. It is based on a Linux kernel module and provides a coarse grained trace of a superset of all the memory accesses performed by an application over its addressing space during the time of its execution. The overhead of Moca is reasonable when taking into account the fact that it is able to collect complete traces which are also more precise than the ones collected by comparable tools.Dans les architectures de calcul hautes performances, le système demémoire est une cause fréquente de baisse de performances. Afind'optimiser une application le.a développeur.euse doit étudier le schémad'accès mémoire de son application et adapter ses algorithmes etstructures de données en conséquence. L'objectif est double : tout d'abordil est nécessaire d'éviter les mauvaise utilisations de la hiérarchiemémoire telles que le faux partage de ligne de cache ou la contentiondans les interconnexion NUMA. De plus il est primordial de tirer lemeilleur parti des différents niveaux de cache et du pré-chargement mémoirematériel.Cependant, la plupart des outils d'analyse de performances se concentrent surdes métriques provenant du processeur. Les rare outils capables de proposerune vue générale des schémas d'accès mémoire se basent sur des mécanismesd'instrumentation matériels et soulèvent deux problèmes. Premièrement ilssont basés sur un échantillonnage dont la précision est limité par lescapacités du matériel. Ensuite ils ne tracent qu'une sous partie des accèsmémoire, en général les plus fréquents, sans informations sur les autresaccès.Dans cette étude, nous présentons Moca un outil efficient de collecte detraces mémoire spatiotemporelles complètes. Cet outil est basé sur unmodule noyau Linux et génère une trace a gros grain contenant unsurensemble des accès mémoire effectués par un application au cours dutemps et de l'espace d'adressage de l'exécution. Le surcout de Moca estraisonnable si on prends en compte le fait que la trace produite estcomplète et donc plus précise que celles produites par des outilscomparable

TABARNAC: Visualizing and Resolving Memory Access Issues on NUMA Architectures

International audienceIn modern parallel architectures, memory accesses represent a common bottleneck. Thus, optimizing the way applications access the memory is an important way to improve performance and energy consumption. Memory accesses are even more important with NUMA machines, as the access time to data depends on its location in the memory. Many efforts were made to develop adaptive tools to improve memory accesses at the runtime by optimizing the mapping of data and threads to NUMA nodes. However, theses tools are not able to change the memory access pattern of the original application, therefore a code written without considering memory performance might not benefit from them. Moreover, automatic mapping tools take time to converge towards the best mapping, losing optimization opportunities. A deeper understanding of the memory behavior can help optimizing it, removing the need for runtime analysis. In this paper, we present TABARNAC , a tool for analyzing the memory behavior of parallel applications with a focus on NUMA architectures. TABARNAC provides a new visualization of the memory access behavior, focusing on the distribution of accesses by thread and by structure. Such visualization allows the developer to easily understand why performance issues occur and how to fix them. Using TABARNAC , we explain why some applications do not benefit from data and thread mapping. Moreover, we propose several code modifications to improve the memory access behavior of several parallel applications. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstracting with credi

Observational Constraints on Submillimeter Dust Opacity

Infrared extinction maps and submillimeter dust continuum maps are powerful probes of the density structure in the envelope of star-forming cores. We make a direct comparison between infrared and submillimeter dust continuum observations of the low-mass Class 0 core, B335, to constrain the ratio of submillimeter to infrared opacity (κ_(smm)/κ_(ir)) and the submillimeter opacity power-law index (κ ∝ λ–β). Using the average value of theoretical dust opacity models at 2.2 μm, we constrain the dust opacity at 850 and 450 μm. Using new dust continuum models based upon the broken power-law density structure derived from interferometric observations of B335 and the infall model derived from molecular line observations of B335, we find that the opacity ratios are ^κ_(850)_κ_(2.2) = (3.21 - 4.80)^(+0.44)_(-0.30) x 10^(-4) ^κ_(450)_κ(2.0) = (12.8-24.8)^(+2.4)_(-1.3) x 10^(-4) with a submillimeter opacity power-law index of β_(smm) = (2.18-2.58)^(+0.30)_(–0.30). The range of quoted values is determined from the uncertainty in the physical model for B335. For an average 2.2 μm opacity of 3800 ± 700 cm^2 g^(–1), we find a dust opacity at 850 and 450 μm of κ_(850) = (1.18-1.77)^9+0.36)_(–0.24) and κ_(450) = (4.72-9.13)^(+1.9)_(–0.98) cm^2 g^(–1) of dust. These opacities are from (0.65-0.97)κ^(OH5)_(850) of the widely used theoretical opacities of Ossenkopf and Henning for coagulated ice grains with thin mantles at 850 μm

Crystalline Silicate Emission in the Protostellar Binary Serpens--SVS20

We present spatially resolved mid-infrared spectroscopy of the class I/flat-spectrum protostellar binary system SVS20 in the Serpens cloud core. The spectra were obtained with the mid-infrared instrument T-ReCS on Gemini-South. SVS20-South, the more luminous of the two sources, exhibits a mid-infrared emission spectrum peaking near 11.3 \micron, while SVS20-North exhibits a shallow amorphous silicate absorption spectrum with a peak optical depth of $\tau \sim 0.3$. After removal of the the line-of-sight extinction by the molecular common envelope, the ``protostar-only'' spectra are found to be dominated by strong amorphous olivine emission peaking near 10 \micron. We also find evidence for emission from crystalline forsterite and enstatite associated with both SVS20-S and SVS20-N. The presence of crystalline silicate in such a young binary system indicates that the grain processing found in more evolved HAeBe and T Tauri pre-main sequence stars likely begins at a relatively young evolutionary stage, while mass accretion is still ongoing.Comment: Accepted for publication by The Astrophysical Journa

Deep Near-Infrared Observations of L1014: Revealing the nature of the core and its embedded source

Recently, the Spitzer Space Telescope discovered L1014-IRS, a mid-infrared source with protostellar colors, toward the heretofore "starless" core L1014. We present deep near-infrared observations that show a scattered light nebula extending from L1014-IRS. This nebula resembles those typically associated with protostars and young stellar objects, tracing envelope cavities presumably evacuated by an outflow. The northern lobe of the nebula has an opening angle of ~100 degrees, while the southern lobe is barely detected. Its morphology suggests that the bipolar cavity and inferred protostellar disk is not inclined more than 30 degrees from an edge-on orientation. The nebula extends at least 8" from the source at Ks, strongly suggesting that L1014-IRS is embedded within L1014 at a distance of 200 pc rather than in a more distant cloud associated with the Perseus arm at 2.6 kpc. In this case, the apparently low luminosity of L1014-IRS, 0.090 Lsun, is consistent with it having a substellar mass. However, if L1014-IRS is obscured by a circumstellar disk, its luminosity and inferred mass may be greater. Using near-infrared colors of background stars, we investigate characteristics of the L1014 molecular cloud core. We determine a mass of 3.6 Msun for regions of the core with Av > 2 magnitudes. A comparison of the radial extinction profile of L1014 with other cores suggests that L1014 may be among the most centrally condensed cores known, perhaps indicative of the earliest stages of brown dwarf or star formation processes.Comment: Replacement includes revision to mass of core. 22 pages, 6 figures. Accepted by Ap

Comparison of monocyte and alveolar macrophage antibody-dependent cellular cytotoxicity and Fc-receptor activity

The cytotoxic potential of rabbit peripheral blood monocytes and alveolar macrophages in antibody-dependent cellular cytotoxicity (ADCC) toward both erythrocyte (RBCox) and tumor cell (CEM T-lymphoblast) targets was examined. ADCC was measured in a 4-hr 51Cr-release assay. Alveolar macrophages were more efficient at killing the tumor cell targets (optimally sensitized with rabbit antisera) than monocytes at similar effector cell/target cell (E/T) ratios. Tumor cell targets sensitized with seven different antisera (anti-CEM) were lysed by alveolar macrophages but not by the monocytes. In marked contrast, the monocytes were more effective at lysing the sensitized erythrocyte target cells. The degree of cytolysis of RBCox and CEM was dependent on the E/T ratio and the degree of sensitization of these target cells. It was demonstrated that the effector cell selectivity in ADCC was directly related to their ability or inability to bind the sensitized target cells as determined by Fc-receptor rosette formation. The transition from monocyte to macrophage may, therefore, have resulted in an alteration in the criteria necessary for Fc-receptor binding to antibody-sensitized target cells and subsequent ADCC.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24214/1/0000473.pd