Experimental realization of decoherence-free subspace in neutron interferometry.
A decoherence-free subspace (DFS) is an important class of quantum-error-correcting (QEC) codes that have been proposed for fault-tolerant quantum computation. The applications of QEC techniques, however, are not limited to quantum-information processing (QIP). Here we demonstrate how QEC codes may be used to improve experimental designs of quantum devices to achieve noise suppression. In particular, neutron interferometry is used as a test bed to show the potential for adding quantum error correction to quantum measurements. We built a five-blade neutron interferometer that incorporates both a standard Mach-Zender configuration and a configuration based on a DFS. Experiments verify that the DFS interferometer is protected against low-frequency mechanical vibrations. We anticipate these improvements will increase the range of applications for matter-wave interferometry.

title: Unified Description of Pion-Photo-Production and Elastic Pion Scattering on the Deuteron in the Isobar-Doorway Model
abstract: It has been recognized recently1 that the strong dominance of the Δ(1236) isobar in nuclear reactions at medium energies advocates an explicit treatment of this degree of freedom in nuclei (in contrast to its implicit incorporation in an optical model description). Such a model, phrased commonly as isobar doorway or A* model1 has two particularly interesting features, (i) it forms a natural basis for a unified description of different isobar dominated scattering processes; (ii) it offers a more or less direct test of the isobar self energy in nuclei or, equivalently, of the ΔN interaction. An ideal testing ground for such a model seems to be deuteron: with all many-body complications being absent, predictions for scattering reactions on the deuteron should reflect and in this way allow direct investigation of the various ingredients of the model.

title: Quark excitations of nuclei - A new frontier in nuclear research -
abstract: The investigation of nuclei in the energy domain of the elementary N*-resonances (i.e. for 200 MeV < Eexc < 2 GeV) opens up a new and important domain of nuclear research for essentially two reasons: (i) the quark structure of the nuclear constituent, the nucleon, leads to new nuclear phenomena; their investigation appears to be of fundamental importance for the understanding of complex hadronic systems; (ii) the nucleus can be used as a unique laboratory to test QCD in the nonasymptotic region where perturbative approaches fail. This is of particular interest, e.g. for the confinement problem. — Some specific aspects of subnuclear research are discussed in connection with the analysis of recent experiments and, in particular, in view of a possible strategy for a systematic investigation of nuclear quark excitations.

title: Light mesons and mesonic states

title: Meson-nucleus interaction - on the use of intensive meson beams for subnuclear research -
abstract: The use of intensive pion and kaon beams for subnuclear research is discussed. The goals of such investigations are briefly sketched and illustrated for some typical examples of specific flavour transfer reactions. It turns out that the meson beams which will be available at the proposed EHF will open up a new aera of subnuclear research. Such investigation touch upon quite fundamental questions of hadronic physics.

title: Measuring the neutron's mean square charge radius using neutron interferometry
abstract: The neutron is electrically neutral, but its substructure consists of charged quarks so it may have an internal charge distribution. In fact it is known to have a negative mean square charge radius (MSCR), the second moment of the radial charge density. In other words the neutron has a positive core and negative skin. In the first Born approximation the neutron MSCR can be simply related to the neutron–electron scattering length b ne . In the past this important quantity has been extracted from the energy dependence of the total transmission cross-section of neutrons on high-Z targets, a very difficult and complicated process. A few years ago S.A. Werner proposed a novel approach to measuring b ne from the neutron's dynamical phase shift in a perfect crystal close to the Bragg condition. We are conducting an experiment based on this method at the NIST neutron interferometer which may lead to a five-fold improvement in precision of b ne and hence the neutron MSCR.

title: Infrared scaling solutions beyond the Landau gauge: The maximally Abelian gauge and Abelian infrared dominance
abstract: Functional equations like exact renormalization group and Dyson-Schwinger equations have contributed to a better understanding of non-perturbative phenomena in quantum field theories in terms of the underlying Green functions. In Yang-Mills theory especially the Landau gauge has been used, as it is the most accessible gauge for these methods. The growing understanding obtained in this gauge allows to proceed to other gauges in order to obtain more information about the relation of different realizations of the confinement mechanism. In the maximally Abelian gauge first results are very encouraging as a variant of Abelian infrared dominance is found: The Abelian part of the gauge field propagator is enhanced at low momenta and thereby dominates the dynamics in the infrared. Its role is therefore similar to that of the ghost propagator in the Landau gauge, where one denotes the corresponding phenomenon as ghost dominance. Also the ambiguity of two different types of solutions (decoupling and scaling) exists in both gauges. Here we present how the two solutions are related in the maximally Abelian gauge. The intricacy of the system of functional equations in this gauge required the development of some new tools and methods as, for example, the automated derivation of the equations by the program DoFun. We also present results for linear covariant and ghost anti-ghost symmetric gauges.

title: Design and performance of a modular low-radioactivity readout system for cryogenic detectors in the CDMS experiment
abstract: The Cryogenic Dark Matter Search (CDMS) experiment employs ultra-cold solid-state detectors to search for rare events resulting from WIMP-nucleus scattering. An innovative detector packaging and readout system has been developed to meet the unusual combination of requirements for: low temperature, low radioactivity, low energy threshold, and large channel count. Features include use of materials with low radioactivity such as multi-layer KAPTON laminates for circuit boards; immunity to microphonic noise via a vacuum coaxial wiring design, manufacturability, and modularity. The detector readout design had to accommodate various electronic components which have to be operated in close proximity to the detector as well maintaining separate individual temperatures (ranging from 600 mK to 150 K) in order to achieve optimal noise performance. The paper will describe the general electrical, thermal, and mechanical designs of the CDMS readout system, as well as presenting the theoretical and measured performance of the detector readout channels.

title: Low-threshold analysis of CDMS shallow-site data
abstract: Data taken during the final shallow-site run of the first tower of the Cryogenic Dark Matter Search (CDMS II) detectors have been reanalyzed with improved sensitivity to small energy depositions. Four {approx}224 g germanium and two {approx}105 g silicon detectors were operated at the Stanford Underground Facility (SUF) between December 2001 and June 2002, yielding 118 live days of raw exposure. Three of the germanium and both silicon detectors were analyzed with a new low-threshold technique, making it possible to lower the germanium and silicon analysis thresholds down to the actual trigger thresholds of {approx}1 and  Limits on the spin-independent cross section for weakly interacting massive particles (WIMPs) to elastically scatter from nuclei based on these data exclude interesting parameter space for WIMPs with masses below 9 GeV/c{sup 2}. Under standard halo assumptions, these data partially exclude parameter space favored by interpretations of the DAMA/LIBRA and CoGeNT experiments data as WIMP signals, and exclude new parameter space for WIMP masses between 3 and 4 GeV/c{sup 2}.

title: Dark Matter Search Results from the CDMS II Experiment
abstract: News from the Dark Side? Dark matter is thought to represent 85% of all matter in the universe and to have been responsible for the formation of structure in the early universe, but its nature is still a mystery. Ahmed et al. (p. 1619, published online 11 February; see the Perspective by Lang) describe the results from the completed Cryogenic Dark Matter Search (CDMS II) experiment, which searched for dark matter in the form of weakly interacting massive particles (WIMP). Two candidate signals were observed, whereas only one background event was expected. The probability of having two or more events from the background would have been 23%. The results of this analysis cannot be interpreted with confidence as evidence for WIMP interactions, but, at the same time, neither event can be ruled out as representing signal. Details of possible, but unlikely, detection events produced by dark matter are reported. Astrophysical observations indicate that dark matter constitutes most of the mass in our universe, but its nature remains unknown. Over the past decade, the Cryogenic Dark Matter Search (CDMS II) experiment has provided world-leading sensitivity for the direct detection of weakly interacting massive particle (WIMP) dark matter. The final exposure of our low-temperature germanium particle detectors at the Soudan Underground Laboratory yielded two candidate events, with an expected background of 0.9 ± 0.2 events. This is not statistically significant evidence for a WIMP signal. The combined CDMS II data place the strongest constraints on the WIMP-nucleon spin-independent scattering cross section for a wide range of WIMP masses and exclude new parameter space in inelastic dark matter models.

title: Revealing Bell’s nonlocality for unstable systems in high energy physics
abstract: Entanglement and its consequences—in particular the violation of Bell inequalities, which defies our concepts of realism and locality—have been proven to play key roles in Nature by many experiments for various quantum systems. Entanglement can also be found in systems not consisting of ordinary matter and light, i.e. in massive meson–antimeson systems. Bell inequalities have been discussed for these systems, but up to date no direct experimental test to conclusively exclude local realism was found. This mainly stems from the fact that one only has access to a restricted class of observables and that these systems are also decaying. In this Letter we put forward a Bell inequality for unstable systems which can be tested at accelerator facilities with current technology. Herewith, the long awaited proof that such systems at different energy scales can reveal the sophisticated “dynamical” nonlocal feature of Nature in a direct experiment gets feasible. Moreover, the role of entanglement and $\mathcal{CP}$ violation, an asymmetry between matter and antimatter, is explored, a special feature offered only by these meson–antimeson systems.