79 research outputs found
Electronic Collective Modes and Superconductivity in Layered Conductors
A distinctive feature of layered conductors is the presence of low-energy
electronic collective modes of the conduction electrons. This affects the
dynamic screening properties of the Coulomb interaction in a layered material.
We study the consequences of the existence of these collective modes for
superconductivity. General equations for the superconducting order parameter
are derived within the strong-coupling phonon-plasmon scheme that account for
the screened Coulomb interaction. Specifically, we calculate the
superconducting critical temperature Tc taking into account the full
temperature, frequency and wave-vector dependence of the dielectric function.
We show that low-energy plasmons may contribute constructively to
superconductivity. Three classes of layered superconductors are discussed
within our model: metal-intercalated halide nitrides, layered organic materials
and high-Tc oxides. In particular, we demonstrate that the plasmon contribution
(electronic mechanism) is dominant in the first class of layered materials. The
theory shows that the description of so-called ``quasi-two-dimensional
superconductors'' cannot be reduced to a purely 2D model, as commonly assumed.
While the transport properties are strongly anisotropic, it remains essential
to take into account the screened interlayer Coulomb interaction to describe
the superconducting state of layered materials.Comment: Final version (minor changes) 14 pages, 6 figure
Quantum walks: a comprehensive review
Quantum walks, the quantum mechanical counterpart of classical random walks,
is an advanced tool for building quantum algorithms that has been recently
shown to constitute a universal model of quantum computation. Quantum walks is
now a solid field of research of quantum computation full of exciting open
problems for physicists, computer scientists, mathematicians and engineers.
In this paper we review theoretical advances on the foundations of both
discrete- and continuous-time quantum walks, together with the role that
randomness plays in quantum walks, the connections between the mathematical
models of coined discrete quantum walks and continuous quantum walks, the
quantumness of quantum walks, a summary of papers published on discrete quantum
walks and entanglement as well as a succinct review of experimental proposals
and realizations of discrete-time quantum walks. Furthermore, we have reviewed
several algorithms based on both discrete- and continuous-time quantum walks as
well as a most important result: the computational universality of both
continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing
Journa
Long-Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE) Conceptual Design Report Volume 2: The Physics Program for DUNE at LBNF
The Physics Program for the Deep Underground Neutrino Experiment (DUNE) at the Fermilab Long-Baseline Neutrino Facility (LBNF) is described
Highly-parallelized simulation of a pixelated LArTPC on a GPU
The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 10^3 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype
Radiocarbon evidence for the Lateglacial human recolonisation of Northern Europe
This paper examines, through the use of Accelerator Mass Spectrometry dating, the database of Lateglacial cultures involved in the recolonisation of northern Europe. The aim is not only to determine the timing of that recolonisation, but also to propose a general model of hunter-gatherer colonisation at a sub-continental scale. The question is addressed of how long the period of abandonment of northern Europe during the WĂŒrm/Weichsel glaciation may have lasted, and when it both started and came to an end. A series of questions is asked concerning the processes and mechanics of recolonisation and the sequences for specific areas are examined. AMS radiocarbon dating shows that a two stage process was involved, which has important implications for our analysis of regional settlement patterns and the changing scale of Lateglacial hunting systems. Recolonisation was a dynamic process, integral to, and internally driven by, the social life of Lateglacial hunters. It may have been constrained by environmental and resource factors, which we have emphasised here, but ultimately it was an historical, social process and should be similarly regarded to that of the farmers. By measuring rates of expansion data are provided for use in other studies of hunter-gatherer colonisation
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