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Interaction effects in one-dimensional helical liquids
No full textHelical liquids are one-dimensional quantum many-body systems where the low-energy excitations have spin and momentum degrees of freedom locked together. They can be realized in several different setups such as semiconducting wires, carbon nanotubes, and ultracold atoms trapped in optical lattices. They also appear as edge states of two-dimensional topological insulators. As a result of spin-momentum locking, they exhibit peculiar transport properties and represent promising platforms for the realization of Majorana fermions when coupled to superconductors; moreover, in the presence of particle-particle interactions, they can enter a fractional helical phase whose low-energy excitations have a fractional charge and a fractional Abelian statistics. In this thesis we study various aspects of interacting one-dimensional helical liquids. Firstly, we consider a one-dimensional chain of alkaline earth-(like) atoms hosting low-energy helical excitations and, by means of the synthetic dimension framework, we show that it is equivalent to an interacting fermionic ladder pierced by a constant magnetic field which displays features related to the quantum Hall effect. In these synthetic ladders, we investigate how helical excitations analogous to the chiral edge modes of the quantum Hall effect are affected by repulsive interactions and we find the existence of a hierarchy of fully gapped phases characterized by peculiar charge and spin orders. Then, we study the charge and the spin patterns of a quantum dot embedded into a spin-orbit coupled quantum wire subject to a magnetic field and we explore how the 2π-periodic and the 4π-periodic Josephson currents in a superconductor-helical liquidsuperconductor hybrid junction are affected by interactions. Finally, we show that, by entangling two identical particles with a qubit, we can transmute the quantum statistics of particles in a scattering experiment which could be realized using the helical edge states of a two-dimensional topological insulator
Erratum: Dissipative Landau-Zener problem and thermally assisted quantum annealing [Physical Review B 96, 0543001 (2017)]
No full textFigure 6 has a typographical error in the key: The labels corresponding to RWA and without the RWA are wrongly switched. The caption as well as all the rest of the paper are nevertheless correct and unaffected by this error. We show the exact figure here below with its original caption from the paper. (Figure Presented)
Optimal working point in dissipative quantum annealing
Full text linkWe study the effect of a thermal environment on the quantum annealing dynamics of a transverse-field Ising chain. The environment is modeled as a single Ohmic bath of quantum harmonic oscillators weakly interacting with the total transverse magnetization of the chain in a translationally invariant manner. We show that the density of defects generated at the end of the annealing process displays a minimum as a function of the annealing time, the so-called optimal working point, only in rather special regions of the bath temperature and coupling strength plane. We discuss the relevance of our results for current and future experimental implementations with quantum annealing hardware
Dissipative Landau-Zener problem and thermally assisted Quantum Annealing
Full text linkWe revisit here the issue of thermally assisted Quantum Annealing by a detailed study of the dissipative Landau-Zener problem in the presence of a Caldeira-Leggett bath of harmonic oscillators, using both a weak-coupling quantum master equation and a quasiadiabatic path-integral approach. Building on the known zero-temperature exact results [Wubs, Phys. Rev. Lett. 97, 200404 (2006)PRLTAO0031-900710.1103/PhysRevLett.97.200404], we show that a finite temperature bath can have a beneficial effect on the ground-state probability only if it couples also to a spin direction that is transverse with respect to the driving field, while no improvement is obtained for the more commonly studied purely longitudinal coupling. In particular, we also highlight that, for a transverse coupling, raising the bath temperature further improves the ground-state probability in the fast-driving regime. We discuss the relevance of these findings for the current quantum-annealing flux qubit chips
Parity dependent Josephson current through a helical Luttinger liquid
Full text linkWe consider a superconductor-two dimensional topological insulator-
superconductor junction (S-2DTI-S) and study how the 2π- and 4π-periodic Josephson
currents are affected by the electron-electron interaction. In the long-junction limit
the supercurrent can by evaluated by modeling the system as a helical Luttinger
liquid coupled to superconducting reservoirs. After having introduced bosonization
in the presence of the parity constraint we turn to consider the limit of perfect and
poor interfaces. For transparent interfaces, where perfect Andreev reflections occur at
the boundaries, the Josephson current is marginally affected by the interaction. On
the contrary, if strong magnetic scatterers are present in the weak link, the situation
changes dramatically. Here Coulomb interaction plays a crucial role both in low and
high temperature regimes. Furthermore, a phase-shift of Josephson current can be
induced by changing the direction of the magnetization of the impurity
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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