Decoherence-free quantum information processing with four-photon entangled states

Decoherence-free states protect quantum information from collective noise, the predominant cause of decoherence in current implementations of quantum communication and computation. Here we demonstrate that spontaneous parametric down conversion can be used to generate four-photon states which enable the encoding of one qubit in a decoherence-free subspace. The immunity against noise is verified by quantum state tomography of the encoded qubit. We show that particular states of the encoded qubit can be distinguished by local measurements on the four photons only.     

Proposed experiment to test the bounds of quantum correlations

The combination of quantum correlations appearing in the Clauser-Horne-Shimony-Holt inequality can give values between the classical bound, 2, and Tsirelson's bound, 2 x square root of 2. However, for a given set of local observables, there are values in this range which no quantum state can attain. We provide the analytical expression for the corresponding bound for a parametrization of the local observables introduced by Filipp and Svozil, and describe how to experimentally trace it using a source of singlet states. Such an experiment will be useful to identify the origin of the experimental errors in Bell's inequality-type experiments and could be modified to detect hypothetical correlations beyond those predicted by quantum mechanics.     

Methode zur Messung von Wärmeeffekten bei Zugverformung

Zusammenfassung Es wird eine mit elektrischer Kompensation arbeitende Me?methode beschrieben, die registrierend die W?rmestr?me in die Umgebung bei gleichzeitiger Aufnahme des Zug-Dehnungsdiagrammes an Borsten und B?ndern zu messen gestattet. Aus der Integration der Kurven ergeben sich die mechanischen Verformungsenergien sowie die gleichzeitig auftretenden W?rmet?nungen: Erreichte Empfindlichkeit: etwa 10⁻⁴ cal. Vorgetragen auf der Arbeitssitzung des Fachausschusses “Physik der Hochpolymeren” im Verband der Deutschen Physikalischen Gesellschaften zur Physikertagung München am 7. September 1956.     

Relaxation-optimized NMR spectroscopy of methylene groups in proteins and nucleic acids

A large fraction of hydrogens in proteins and nucleic acids is of the methylene type. Their detailed study, however, in terms of structure and dynamics by NMR spectroscopy is hampered by their fast relaxation properties, which give rise to low sensitivity and resolution. It is demonstrated that six different relaxation interference processes, involving 1H-13C and 1H-1H dipolar interactions and 1H and 13C chemical shift anisotropy, can be used simultaneously to mitigate these problems effectively. The approach is applicable to the majority of NMR experiments commonly used to study side chain and backbone conformation. For proteins, its efficiency is evaluated quantitatively for two samples: the third IgG-binding domain from Streptococcal Protein G and the protein calmodulin complexed with a 26-residue target peptide. Gains in both resolution and sensitivity by up to factors of 3.2 and 2.0, respectively, are observed for Gly residues at high magnetic field strengths, but even at much lower fields gains remain substantial. The resolution enhancement obtained for methylene groups makes possible a detailed analysis of spectral regions commonly considered inaccessible due to spectral crowding. For DNA, the high resolution now obtainable for C5' sites permits an H5'/H5'-based sequential NOE assignment procedure, complementary to the conventional base-H1'/H2'/H2' pathway.     

Unexpected properties of locally presentable categories

Locally presentable categories are precisely those complete categories which have a small dense subcategory. Every subcategory of a locally presentable category (i) has a small dense subcategory, (ii) if it is closed under limits, then it is locally presentable and (iii) if it is closed under colimits, then it is coreflective. For density, canonical colimits can be substituted by arbitrary colimits.The above results hold under the assumption of the set-theoretical Vopenka's Principle; in fact, each of them is logically equivalent to that principle.In Memory of Evelyn NelsonPresented by Ervin Fried.     

Deactivation processes of homogeneous Pd catalysts using in situ time resolved spectroscopic techniques

UV-Vis, combined with ED-XAFS shows, for the first time, the evolution of inactive Pd dimers and trimers, that are a possible first stage in the deactivation process of important palladium catalysed reactions, leading to larger palladium clusters and eventually palladium black.     

Bell's theorem without inequalities and without alignments

A proof of Bell's theorem without inequalities is presented which exhibits three remarkable properties: (a). reduced local states are immune to collective decoherence; (b). distant local setups do not need to be aligned, since the required perfect correlations are achieved for any local rotation of the local setups; (c). local measurements require only individual measurements on the qubits. Indeed, it is shown that this proof is essentially the only one which fulfills (a). (b). and (c).     

Accumulation of dwell times in light diffusion

We discuss various speeds of propagation that are relevant for the dynamics of classical waves in random media: phase velocity, group velocity and transport velocity. The transport velocity can be much smaller than the phase velocity due to the long dwelling of classical waves inside resonant scatterers. We show that the transport velocity of light can be obtained experimentally by study both transient and steady-state diffusion of light.