Dressed tunneling approximation for electronic transport through molecular transistors

A theoretical approach for the non-equilibrium transport properties of nanoscale systems coupled to metallic electrodes with strong electron-phonon interactions is presented. It consists in a resummation of the dominant Feynman diagrams from the perturbative expansion in the coupling to the leads. We show that this scheme eliminates the main pathologies found in previous simple analytical approaches for the polaronic regime. The results for the spectral and transport properties are compared with those from several other approaches for a wide range of parameters. The method can be formulated in a simple way to obtain the full counting statistics. Results for the shot and thermal noise are presented.Comment: 11 pages, 11 figures. Accepted for publication in Physical Review

Creating and detecting poor man's Majorana bound states in interacting quantum dots

We propose and theoretically investigate an alternative way to create the poor man's Majorana bound states (MBSs) introduced in Phys. Rev. B 86, 134528 (2012). Our proposal is based on two quantum dots (QDs) with strong electron-electron interactions that couple via a central QD with proximity-induced superconductivity. In the presence of spin-orbit coupling and a magnetic field, gate control of all three QDs allows tuning the system into sweet spots with one MBS localized on each outer dot. We quantify the quality of these MBSs and show how it depends on the Zeeman energy and interaction strength. We also show how nonlocal transport spectroscopy can be used to identify sweet spots with high MBS quality. Our results provide a path for investigating MBS physics in a setting that is free of many of the doubts and uncertainties that plague other platforms.Comment: 10 pages, 8 figure

Topological superconductivity in a magnetic-texture coupled Josephson junction

Topological superconductors are appealing building blocks for robust and reliable quantum information processing. Most platforms for engineering topological superconductivity rely on a combination of superconductors, materials with intrinsic strong spin-orbit coupling, and external magnetic fields, detrimental for superconductivity. We propose a setup where a conventional Josephson junction is linked via a magnetic-textured barrier. Antiferromagnetic and ferromagnetic insulators with periodically arranged domains are compatible with our proposal which does not require intrinsic spin-orbit or external magnetic fields. We find that the topological phase depends on the magnitude and period of the barrier magnetization. The superconducting phase controls the topological transition, which could be detected as a sharp suppression of the supercurrent across the junction.Comment: 18 pages, 10 figure

La pérdida de Rb1 modula la respuesta al daño en el ADN y la senescencia inducida por estrés oncogénico favoreciendo la progresión tumoral

La estimulación de señales oncogénicas en células primarias provoca la activación de senescencia inducida por oncogénesis (OIS), uno de los principales mecanismos de supresión tumoral. Recientemente se ha descrito que la activación de OIS responde a la activación de checkpoints dependientes de daño en el DNA (DDR), salvaguardando la integridad del genoma. En este trabajo se ha demostrado como los mecanismos celulares implicados en el proceso de transformación de los gliomas son capaces de desacoplar ambos procesos, OIS y DDR. Los gliomas humanos se caracterizan por presentar alteraciones en vías de señalización intracelulares, así como alteraciones en la regulación del ciclo celular. En muestro modelo de gliomagénesis, estas alteraciones han sido recreadas a través de la expresión de Ras oncogénico (HRasV12) e inactivación del gen de Rb1 respectivamente. Sorprendentemente, la expresión de HRasV12 en astrocitos, no es capaz de inducir senescencia celular, a pesar del aumento en los niveles de p53, p16INK4a y p21CIP1, como ha sido descrito en otros tipos celulares. Sin embargo, la activación de esta vía oncogénica es suficiente para incrementar la tasa de proliferación, estimular la producción de especies reactivas del oxígeno (ROS) y generar inestabilidad genómica, llegando a inducir la formación de tumores con características similares a gliomas de bajo grado. Estos resultados difieren cuando la acción oncogénica de Ras va acompañada de la pérdida del supresor de tumores Rb1. En este escenario, la deleción del gen Rb1 confiere una ventaja proliferativa a los astrocitos, además de aumentar la activación de DDR de forma independiente de daño en el DNA

Interference and parity blockade in transport through a Majorana box

A Majorana box - two topological superconducting nanowires coupled via a trivial superconductor - is a building block in devices aiming to demonstrate nonabelian physics, as well as for topological quantum computer architectures. We theoretically investigate charge transport through a Majorana box and show that current can be blocked when two Majoranas couple to the same lead, fixing their parity. In direct analogy to Pauli spin blockade in spin qubits, this parity blockade can be used for fast and high-fidelity qubit initialization and readout, as well as for current-based measurements of decoherence times. Furthermore, we demonstrate that transport can distinguish between a clean Majorana box and a disordered box with additional unwanted Majorana or Andreev bound states.Comment: 4 pages, 3 figures + 6 pages supplementar

Persistent current noise in narrow Josephson junctions

Josephson junctions have broad applications in metrology, quantum information processing, and remote sensing. For these applications, the electronic noise is a limiting factor. In this work we study the thermal noise in narrow Josephson junctions using a tight-binding Hamiltonian. For a junction longer than the superconducting coherence length, several self-consistent gap profiles appear close to a phase difference $\pi$. They correspond to two stable solutions with an approximately constant phase gradient over the thin superconductor connected by a $2\pi$ phase slip, and a solitonic branch. The current noise power spectrum has pronounced peaks at the transition frequencies between the different states in each branch. We find that the noise is reduced in the gradient branches in comparison to the zero-length junction limit. In contrast, the solitonic branch exhibits an enhanced noise and a reduced current due to the pinning of the lowest excitation energy to close to zero energy.Comment: 4+epsilon pages (2 pages Supplemental), 4 figures (3 figures Supplemental

Hybrid Overlap Filter for LiDAR Point Clouds Using Free Software

Despite the large amounts of resources destined to developing filtering algorithms of LiDAR point clouds in order to obtain a Digital Terrain Model (DTM), the task remains a challenge. As a society advancing towards the democratization of information and collaborative processes, the researchers should not only focus on improving the efficacy of filters, but should also consider the users’ needs with a view toward improving the usability and accessibility of the filters in order to develop tools that will provide solutions to the challenges facing this field of study. In this work, we describe the Hybrid Overlap Filter (HyOF), a new filtering algorithm implemented in the free R software environment. The flow diagram of HyOF differs in the following ways from that of other filters developed to date: (1) the algorithm is formed by a combination of sequentially operating functions (i.e., the output of the first function provides the input of the second), which are capable of functioning independently and thus enabling integration of these functions with other filtering algorithms; (2) the variable penetrability is defined and used, along with slope and elevation, to identify ground points; (3) prior to selection of the seed points, the original point cloud is processed with the aim of removing points corresponding to buildings; and (4) a new method based on a moving window, with longitudinal overlap between windows and transverse overlap between passes, is used to select the seed points. Our hybrid filtering method is tested using 15 reference samples acquired by the International Society of Photogrammetry and Remote Sensing (ISPRS) and is evaluated in comparison with 33 existing filtering algorithms. The results show that our hybrid filtering method produces an average total error of 3.34% and an average Kappa coefficient of 92.62%. The proposed algorithm is one of the most accurate filters that has been tested with the ISPRS reference samplesThis research was funded by the Project Red de Tecnoloxías LiDAR e de Información Xeoespacial (Plan Galego 2011–2015 (Plan I2C): Programa Consolidación e Estructuración (Redes)-CN 2012/323)S