5,497 research outputs found
Observation of cooper pair splitting and andreev bound states in carbon nanotubes
Get PDFIn this thesis, we investigate Cooper pair splitting in double quantum dot devices made from carbon nanotubes. We present transport measurements in which the controlled splitting of Cooper pairs dominates the current through such a device, reaching unprecedented splitting efficiencies of up to 90%.
In another experiment we use Cooper pair splitting (and a related non-local transport processes) as a tool to investigate Andreev bound states. Andreev bound states are a key concept in mesoscopic superconductivity. They can form due to the penetration of Cooper pairs into a quantum dot, leading to a new type of energy level that differs drastically from conventional particle-in-a-box states
Andreev Modes from Phase Winding in a Full-Shell Nanowire-Based Transmon
Get PDFWe investigate transmon qubits made from semiconductor nanowires with a fully surrounding superconducting shell. In the regime of reentrant superconductivity associated with the destructive Little-Parks effect, numerous coherent transitions are observed in the first reentrant lobe, where the shell carries 2π winding of superconducting phase, and are absent in the zeroth lobe. As junction density was increased by gate voltage, qubit coherence was suppressed then lost in the first lobe. These observations and numerical simulations highlight the role of winding-induced Andreev states in the junction.BUS/Quantum Delf
Andreev bound states in superconductor/ferromagnet point contact Andreev reflection spectra
Get PDFAs charge carriers traverse a single superconductor ferromagnet interface, they experience an additional spin-dependent phase angle that results in spin mixing and the formation of a bound state called the Andreev bound state. Here we explore whether point contact Andreev reflection can be used to detect the Andreev bound state and, within the limits of our experiment, we extract the resulting spin mixing angle. By examining spectra taken from
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junctions, together with a compilation of literature data on highly spin polarized systems, we suggest that the existence of the Andreev bound state would resolve a number of long standing controversies in the literature of Andreev reflection, as well as defining a route to quantify the strength of spin mixing at superconductor-ferromagnet interfaces. Intriguingly, we find that for high transparency junctions, the spin mixing angle appears to take a relatively narrow range of values across all the samples studied. The ferromagnets we have chosen to study share a common property in terms of their spin arrangement, and our observations may point to the importance of this property in determining the spin mixing angle under these circumstances
Microwave Susceptibility Observation of Interacting Many-Body Andreev States
No full textElectrostatic charging affects the many-body spectrum of Andreev states, yet its influence on their microwave properties has not been elucidated. We developed a circuit quantum electrodynamics probe that, in addition to transition spectroscopy, measures the microwave susceptibility of different states of a semiconductor nanowire weak link with a single dominant (spin-degenerate) Andreev level. We found that the microwave susceptibility does not exhibit a particle-hole symmetry, which we qualitatively explain as an influence of Coulomb interaction. Moreover, our state-selective measurement reveals a large, ?-phase shifted contribution to the response common to all many-body states which can be interpreted as arising from a phase-dependent continuum in the superconducting density of states.BUS/Quantum DelftQRD/Geresdi La
Oscillations of Andreev states in clean ferromagnetic films
No full textWe investigate the influence of the exchange field on the Andreev bound states in a ferromagnetic (F) film backed on one side by a superconductor (S). Our model accounts for diffusive reflection at the outer surface and possible backscattering at the FS interface. Phase shifting of the Andreev level by the exchange field results in an oscillatory behavior of the density of states of F as a function of the layer thickness. We show that our results agree quantitatively with recent experiments.publishe
Transient electromagnetic fields generated in experiments at the PHELIX laser facility
No full textLarge-amplitude electromagnetic radiofrequency fields are created by the charge-separation induced in interactions of high-intensity, short-pulse lasers with solid targets and have intensity that decreases with the distance from the target. Alternatively, it was experimentally proved very recently that charged particles emitted by petawatt laser-target interactions can be deposited on a capacitor-collector structure, far away from the target, and lead to the rapid (nanosecond-scale) generation of large quasi-static electric fields , over wide regions. We demonstrate here the generation of both these fields in experiments at the PHELIX laser facility, with approximately energy and approximately intensity, for picoseconds laser pulses, interacting with pre-ionized polymer foams of near critical density. Quasi-static fields, up to tens of kV/m, were here observed at distances larger than from the target, with results much higher than the radiofrequency component. This is of primary importance for inertial-confinement fusion and laser-plasma acceleration and also for promising applications in different scenarios
Andreev molecules in semiconductor nanowire double quantum dots
Get PDFQuantum simulation is a way to study unexplored Hamiltonians by mapping them onto the assemblies of well-understood quantum systems 1 such as ultracold atoms in optical lattices 2 , trapped ions 3 or superconducting circuits 4 . Semiconductor nanostructures which form the backbone of classical computing hold largely untapped potential for quantum simulation 5–7. In particular, chains of quantum dots in semiconductor nanowires can be used to emulate one-dimensional Hamiltonians such as the toy model of a topological p-wave superconductor 8–11 . Here we realize a building block of this model, a double quantum dot with superconducting 1 contacts, in an indium antimonide nanowire 12 . In each dot, tunnel-coupling to a superconductor induces Andreev bound states 13–19 . We demonstrate that these states hybridize to form the double-dot Andreev molecular states. We establish the parity and the spin structure of Andreev molecular levels by monitoring their evolution in electrostatic potential and magnetic field. Understanding Andreev molecules is a key step towards building longer chains which are predicted to generate Majorana bound states at the end sites 20, 21 . Two supercon ducting quantum dots are already sufficient to test the fusion rules of Majorana bound states, a milestone towards fault-tolerant topological quantum computing
N. S. Gumilyov in the light of the “new Hesychasm” by D. Andreev
Get PDFThe problem of N. S. Gumilyov’s philosophical and artistic reception in the work of D. Andreev is considered. Works devoted to the Russian writer N. S. Gumilev are investigated in connection with this. The relevance of the research is due to the need to state and highlight the problems of the Hesychast traditions in the work of Andreev, since the very life and work of the author of the “Rose of the World” became a continuation of the Russian Hesychastic spiritual, cultural and artistic tradition in the twentieth century. The definitions of the concepts “new Hesychasm by D. Andreev”, “Metaisihazm” are given. The novelty of the research is seen in the fact that for the first time in literary criticism the problem of the “new Hesychasm” of D. Andreev is raised. The Hesychast interpretation of the image and fate of Gumilyov is revealed. A classification of Hesychast practices of spiritual achievement is proposed, which Andreev refers to in order to characterize his older brother of the quill. The results of a comparative analysis of key lexemes in the works of Gumilev and Andreev are presented. The presence of these lexical markers is considered as evidence of a poetic dialogue, a convergence of poets through the decades. The significance of this dialogue in the construction of the metahistorical and life-giving poetic world of D. Andreev is revealed. The question regarding the interpretation of the image of N. S. Gumilev as a symbol of the “ennobled man” in the “Rose of the World” by D. Andreev is raised
Direct Microwave Measurement of Andreev-Bound-State Dynamics in a Semiconductor-Nanowire Josephson Junction
No full textThe modern understanding of the Josephson effect in mesosopic devices derives from the physics of Andreev bound states, fermionic modes that are localized in a superconducting weak link. Recently, Josephson junctions constructed using semiconducting nanowires have led to the realization of superconducting qubits with gate-tunable Josephson energies. We have used a microwave circuit QED architecture to detect Andreev bound states in such a gate-tunable junction based on an aluminum-proximitized indium arsenide nanowire. We demonstrate coherent manipulation of these bound states, and track the bound-state fermion parity in real time. Individual parity-switching events due to nonequilibrium quasiparticles are observed with a characteristic timescale Tparity=160±10 μs. The Tparity of a topological nanowire junction sets a lower bound on the bandwidth required for control of Majorana bound states.QRD/Kouwenhoven LabQRD/Geresdi La
A semiotic analysis of the short stories of Leonid Andreyev, 1900-1909
Get PDFThis thesis applies the techniques of semiotic analysis to a selection of short stories by Leonid Andreyev in an attempt to offer one answer to the problems of categorising Andreyev's unique art and placing it within a literary-evolutionary perspective. The semiotic method was chosen because of its ability both to assimilate literary texts to the supra-individual processes with which it works, and at the same time to delineate an author's particular contribution to these processes. Drawing on a range of literary theory from early Russian Formalism onwards, the study proceeds from one level to another according to a principle of "degree of abstraction", so that each level constitutes firstly an independent account of Andreyev's texts in itself, and secondly one stage in an overall analysis. The analysis at each level pinpoints, in its own terms, a series of semiotic tensions or clashes as being at the heart of Andreyev's literary system. Conflict within his stories between the principles of poetry and prose, metaphor and metonymy, 'discourse' and 'story' and between codes of allegory and codes of reference are among the major tensions highlighted. These tensions are in turn used to account for the fantastic element in Andreyev's stories (tension and ambiguity being the key features of Fantastic literature as defined by many literary theoreticians).The unique, Andreyevan version of the Fantastic is viewed as an index of Andreyev's position in literary evolution at a point of transition between an older, authoritative, transitive mode of narration and a more recent, non-authoritative mode which has come to dominate much twentieth-century literature. The final reference-point for all these tensions is demonstrated to be a shift in modern culture as a whole towards a more impersonal. Mythic thought-system, a shift at the centre of which the art of Leonid Andreyev can be convincingly placed. The material drawn upon includes, in addition to the corpus of Andreyev stories specified, a wide range of works by Andreyev's contemporaries and also the hitherto unexploited draft-manuscripts to a number of Andreyev stories held in the Hoover Institution, U.S.A.A Glossary of the most commonly used theoretical terms is provided at the end of the study
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