Exclusive pi^+ production at HERMES

Hard exclusive production in deep inelastic lepton scattering provides access to the unknown Generalized Parton Distributions (GPDs) of the nucleon. At HERMES, different observables for hard exclusive pi^+ production have been measured with a 27.6 GeV positron beam on an internal hydrogen gas target. First preliminary results for the unpolarized ep->enpi^+ total cross section for 1.5<Q^2<10.5 GeV^2 and for 0.02<x<0.8 are presented and compared to GPD calculations. The final result for the single-spin asymmetry using a longitudinal polarized target is also reported.Comment: 5 pages, 3 figures, contribution to the XII International Workshop on Deep Inelastic Scattering, April 14-18, 2004, Strbske Pleso, Slovaki

The Spin Structure of the Nucleon

This article reviews our present understanding of QCD spin physics: the proton spin puzzle and new developments aimed at understanding the transverse structure of the nucleon. We discuss present experimental investigations of the nucleon's internal spin structure, the theoretical interpretation of the different measurements and the open questions and challenges for future investigation.Comment: Review, 43 pages, 23 figures, to appear in Reviews of Modern Physic

A photonic crystal Josephson traveling wave parametric amplifier

An amplifier combining noise performances as close as possible to the quantum limit with large bandwidth and high saturation power is highly desirable for many solid state quantum technologies such as high fidelity qubit readout or high sensitivity electron spin resonance for example. Here we introduce a new Traveling Wave Parametric Amplifier based on Superconducting QUantum Interference Devices. It displays a 3 GHz bandwidth, a -102 dBm 1-dB compression point and added noise near the quantum limit. Compared to previous state-of-the-art, it is an order of magnitude more compact, its characteristic impedance is in-situ tunable and its fabrication process requires only two lithography steps. The key is the engineering of a gap in the dispersion relation of the transmission line. This is obtained using a periodic modulation of the SQUID size, similarly to what is done with photonic crystals. Moreover, we provide a new theoretical treatment to describe the non-trivial interplay between non-linearity and such periodicity. Our approach provides a path to co-integration with other quantum devices such as qubits given the low footprint and easy fabrication of our amplifier.Comment: 6 pages, 4 figures, Appendixe

Fast high fidelity quantum non-demolition qubit readout via a non-perturbative cross-Kerr coupling

Qubit readout is an indispensable element of any quantum information processor. In this work, we experimentally demonstrate a non-perturbative cross-Kerr coupling between a transmon and a polariton mode which enables an improved quantum non-demolition (QND) readout for superconducting qubits. The new mechanism uses the same experimental techniques as the standard QND qubit readout in the dispersive approximation, but due to its non-perturbative nature, it maximizes the speed, the single-shot fidelity and the QND properties of the readout. In addition, it minimizes the effect of unwanted decay channels such as the Purcell effect. We observed a single-shot readout fidelity of 97.4% for short 50 ns pulses, and we quantified a QND-ness of 99% for long measurement pulses with repeated single-shot readouts

Understanding the saturation power of Josephson Parametric Amplifiers made from SQUIDs arrays

We report on the implementation and detailed modelling of a Josephson Parametric Amplifier (JPA) made from an array of eighty Superconducting QUantum Interference Devices (SQUIDs), forming a non-linear quarter-wave resonator. This device was fabricated using a very simple single step fabrication process. It shows a large bandwidth (45 MHz), an operating frequency tunable between 5.9 GHz and 6.8 GHz and a large input saturation power (-117 dBm) when biased to obtain 20 dB of gain. Despite the length of the SQUID array being comparable to the wavelength, we present a model based on an effective non-linear LC series resonator that quantitatively describes these figures of merit without fitting parameters. Our work illustrates the advantage of using array-based JPA since a single-SQUID device showing the same bandwidth and resonant frequency would display a saturation power 15 dB lower.Comment: 12 pages, 9 figures, Appendices include

The HERMES Back Drift Chambers

The tracking system of the HERMES spectrometer behind the bending magnet consists of two pairs of large planar 6-plane drift chambers. The design and performance of these chambers is described. This description comprises details on the mechanical and electronical design, information about the gas mixture used and its properties, results on alignment, calibration, resolution, and efficiencies, and a discussion of the experience gained through the first three years of operation.Comment: 21 pages, LaTex, 16 figures include

DVCS and hard exclusive meson production

Hard exclusive processes have come to the frontier of nucleon structure physics as they offer experimental access to the Generalised Parton Distributions (GPDs). GPDs have quickly risen in importance as they provide a basis for novel representations of the nucleon as an extended object in space (“nucleon tomography”). A lot of excitement about GPDs is connected to the unique possibility for providing access to the total angular momentum carried by quarks and gluons in the nucleon, a question of fundamental importance in QCD spin physics. This contribution aims at giving an overview about existing measurements of hard exclusive processes, which span over a wide kinematic range, as provided by the HERA collider experiments till the JLab fixed target experiments. A brief summary about the status of GPD extractions in global analyses of these data is given as well. More detailed discussions of the various measurements as well as of model calculations and phenomenology of GPDs can be found at http://ecsac.ictp.it/transversity2011/programma.php