Supercurrent Spectroscopy of Andreev States

We measure the excitation spectrum of a superconducting atomic contact. In addition to the usual continuum above the superconducting gap, the single particle excitation spectrum contains discrete, spin-degenerate Andreev levels inside the gap. Quasiparticle excitations are induced by a broadband on-chip microwave source and detected by measuring changes in the supercurrent flowing through the atomic contact. Since microwave photons excite quasiparticles in pairs, two types of transitions are observed: Andreev transitions, which consists of putting two quasiparticles in an Andreev level, and transitions to odd states with a single quasiparticle in an Andreev level and the other one in the continuum. In contrast to absorption spectroscopy, supercurrent spectroscopy allows detection of long-lived odd states.Comment: typos correcte

Theory of microwave spectroscopy of Andreev bound states with a Josephson junction

We present a microscopic theory for the current through a tunnel Josephson junction coupled to a non-linear environment, which consists of an Andreev two-level system coupled to a harmonic oscillator. It models a recent experiment [Bretheau, Girit, Pothier, Esteve, and Urbina, Nature (London) 499, 312 (2013)] on photon spectroscopy of Andreev bound states in a superconducting atomic-size contact. We find the eigenenergies and eigenstates of the environment and derive the current through the junction due to inelastic Cooper pair tunneling. The current-voltage characteristic reveals the transitions between the Andreev bound states, the excitation of the harmonic mode that hybridizes with the Andreev bound states, as well as multi-photon processes. The calculated spectra are in fair agreement with the experimental data.Comment: 8 pages, 6 figure

Exciting Andreev pairs in a superconducting atomic contact

The Josephson effect describes the flow of supercurrent in a weak link, such as a tunnel junction, nanowire, or molecule, between two superconductors. It is the basis for a variety of circuits and devices, with applications ranging from medicine to quantum information. Currently, experiments using Josephson circuits that behave like artificial atoms are revolutionizing the way we probe and exploit the laws of quantum physics. Microscopically, the supercurrent is carried by Andreev pair states, which are localized at the weak link. These states come in doublets and have energies inside the superconducting gap. Existing Josephson circuits are based on properties of just the ground state of each doublet and so far the excited states have not been directly detected. Here we establish their existence through spectroscopic measurements of superconducting atomic contacts. The spectra, which depend on the atomic configuration and on the phase difference between the superconductors, are in complete agreement with theory. Andreev doublets could be exploited to encode information in novel types of superconducting qubits.Comment: Submitted to Natur

Tunable Superconducting Phase Transition in Metal-Decorated Graphene Sheets

Using typical experimental techniques it is difficult to separate the effects of carrier density and disorder on the superconducting transition in two dimensions. Using a simple fabrication procedure based on metal layer dewetting, we have produced graphene sheets decorated with a non-percolating network of nanoscale tin clusters. These metal clusters both efficiently dope the graphene substrate and induce long-range superconducting correlations. This allows us to study the superconducting transition at fixed disorder and variable carrier concentration. We find that despite structural inhomogeneity on mesoscopic length scales (10-100 nm), this material behaves electronically as a homogenous dirty superconductor. Our simple self-assembly method establishes graphene as an ideal tunable substrate for studying induced two-dimensional electronic systems at fixed disorder and our technique can readily be extended to other order parameters such as magnetism

Superconducting atomic contacts inductively coupled to a microwave resonator

We describe and characterize a microwave setup to probe the Andreev levels of a superconducting atomic contact. The contact is part of a superconducting loop inductively coupled to a superconducting coplanar resonator. By monitoring the resonator reflection coefficient close to its resonance frequency as a function of both flux through the loop and frequency of a second tone we perform spectroscopy of the transition between two Andreev levels of highly transmitting channels of the contact. The results indicate how to perform coherent manipulation of these states.Comment: 14 pages, 10 figures, to appear in special issue on break-junctions in JOPC

Dynamics of quasiparticle trapping in Andreev levels

We present a theory describing the trapping and untrapping of quasiparticles in the Andreev bound level of a single-channel weak link between two superconductors. We calculate the rates of the transitions between even and odd occupations of the Andreev level induced by absorption and emission of both photons and phonons. We apply the theory to a recent experiment [Phys. Rev. Lett. 106, 257003 (2011)] in which the dynamics of the trapping of quasiparticles in the Andreev levels of superconducting atomic contacts coupled to a Josephson junction was measured. We show that the plasma energy $h\nu_p$ of the Josephson junction defines a rather abrupt transition between a fast relaxation regime dominated by coupling to photons and a slow relaxation regime dominated by coupling to phonons. With realistic parameters the theory provides a semi-quantitative description of the experimental results.Comment: 11 pages, 9 figures. Accepted for publication in Physical Review

On the Precision of Search Engines: Results from a Controlled Experiment

Handling the growing amount of digital information is one of the major challenges when dealing with the World Wide Web (WWW). In particular, users crave for an effective and efficient retrieval of needed information. In this context, search engines adopt a key role. Besides conventional search engines such as Google, semantic search engines have emerged as an alternative approach in recent years. The quality of search results delivered by search engines is in influenced by many criteria. This paper picks up one specific issue, the precision, and investigates and compares the precision of current both conventional (i.e., non-semantic) and semantic search engines based on a controlled experiment with 77 participants. Specifically, Google, AltaVista, MetaGer, Hakia, Kngine, and WolframAlpha are investigated and compared

Male nudity in ancient Mesopotamian art

Ankara : The Department of Archaeology, İhsan Doğramacı Bilkent University, 2012.Thesis (Master's) -- Bilkent University, 2012.Includes biblioraphical references 83-89.This thesis attempts to study nude male representations in Mesopotamian art. It analyzes examples of male nudity in art and textual material from the Protoliterate to the Neo-Assyrian period in Northern and Southern Iraq. It aims to investigate the implications that the male nudity in Mesopotamian art carries and both the social and conceptual aspects that are attributed to male nudity in Mesopotamian society. It argues how nude male representations are embedded within cultural, religious and political aspects of the society. The thesis also shows the context dependent state of male nudity and how it is used as a marker in ancient Mesopotamian art pointing to various identities, physicalities, and political and religious configurations.Girit, AyşenM.S

Effects of Hypermobility on Schober Test and Chest Expansion Scores

DergiPark: 420774tmsjAims: Hypermobility is a condition which increases the joint mobility range. Beighton method is used in diagnosisof hypermobility. Schober test and chest expansion measurement are frequently used to evaluate mobility of spineand expansion ability of chest in ankylosing spondylitis volunteers. In this study, it is aimed to investigate the impactof hypermobility on Schober test and chest expansion.Methods: The data of 300 healthy volunteers aged between 18 and 32 was collected. Beighton score, chest expansionand Schober score of all volunteers were measured and statistically analyzed using SPSS. Student’s t-test wasperformed to compare both groups. As for descriptive statistics, mean ± standard deviation and numbers were used.Results: One hundred twenty-two cases having Beighton score of 4 and above included in hypermobility groupwhile 178 cases under 4 served as control group without hypermobility. No significant relation in terms of chest expansionand Schober score was found out between groups. There was a slight positive correlation between Beightonscore and Schober score in whole group. In male population, both test scores had a correlation with Beighton scorewhile only chest expansion had correlation in female population.Conclusion: Although Beighton score seemed to have no effect on Schober or chest expansion scores in betweengroup comparisons, correlation analysis revealed that hypermobility may affect the scores, especially in males