Floquet Majorana Fermions in superconducting quantum dots

We consider different configurations of ac driven quantum dots coupled to superconductor leads where Majorana fermions can exist as collective quasiparticles. The main goal is to tune the existence, localization and properties of these zero energy quasiparticles by means of periodically driven external gates. In particular, we analyze the relevance of the system and driving symmetry. We predict the existence of different sweet spots with Floquet Majorana fermions in configurations where they are not present in the undriven system.Comment: Contribution to the Physica E special issue on "Frontiers in quantum electronic transport" - in memory of Markus B\"uttike

DIMENSIONALITY REDUCTION WITH IMAGE DATA

A common objective in image analysis is dimensionality reduction. The most common often used data-exploratory technique with this objective is principal component analysis. We propose a new method based on the projection of the images as matrices after a Procrustes rotation and show that it leads to a better reconstruction of images.

Degenerate parametric oscillation in quantum membrane optomechanics

The promise of innovative applications has triggered the development of many modern technologies capable of exploiting quantum effects. But in addition to future applications, such quantum technologies have already provided us with the possibility of accessing quantum-mechanical scenarios that seemed unreachable just a few decades ago. With this spirit, in this work we show that modern optomechanical setups are mature enough to implement one of the most elusive models in the field of open system dynamics: degenerate parametric oscillation. The possibility of implementing it in nonlinear optical resonators was the main motivation for introducing such model in the eighties, which rapidly became a paradigm for the study of dissipative phase transitions whose corresponding spontaneously broken symmetry is discrete. However, it was found that the intrinsic multimode nature of optical cavities makes it impossible to experimentally study the model all the way through its phase transition. In contrast, here we show that this long-awaited model can be implemented in the motion of a mechanical object dispersively coupled to the light contained in a cavity, when the latter is properly driven with multi-chromatic laser light. We focus on membranes as the mechanical element, showing that the main signatures of the degenerate parametric oscillation model can be studied in state-of-the-art setups, thus opening the possibility of studying spontaneous symmetry breaking and enhanced metrology in one of the cleanest dissipative phase transitions.Comment: We welcome comments, suggestions, and (constructive) criticis

Dimensionality reduction with image data

A common objective in image analysis is dimensionality reduction. The most common often used data-exploratory technique with this objective is principal component analysis. We propose a new method based on the projection of the images as matrices after a Procrustes rotation and show that it leads to a better reconstruction of images

Transport, shot noise, and topology in AC-driven dimer arrays

We analyze an AC-driven dimer chain connected to a strongly biased electron source and drain. It turns out that the resulting transport exhibits fingerprints of topology. They are particularly visible in the driving-induced current suppression and the Fano factor. Thus, shot noise measurements provide a topological phase diagram as a function of the driving parameters. The observed phenomena can be explained physically by a mapping to an effective time-independent Hamiltonian and the emergence of edge states. Moreover, by considering quantum dissipation, we determine the requirements for the coherence properties in a possible experimental realization. For the computation of the zero-frequency noise, we develop an efficient method based on matrix-continued fractions.Comment: 8 pages, 6 figure

The role of purinergic receptor A1 in neurogenesis modulation from subventricular zone

138 p.La neurogénesis continúa en la edad adulta en regiones específicas del cerebro como la zona subgranular del hipocampo y la zona subventricular (SVZ) de los ventrículos laterales. Resultados previos de nuestro laboratorio demostraron que el ATP liberado tras la deprivación de oxígeno y glucosa inhibe la neurogénesis adulta. Por lo tanto, nuestro objetivo es determinar el papel de la adenosina, uno de los productos de la hidrólisis del ATP, en la modulación de la neurogénesis. Los resultados obtenidos demuestran que altas concentraciones de adenosina (100¿M) inhiben la diferenciación neuronal en cultivos de neuroesferas de la SVZ. Las células multipotentes de la SVZ expresan todos los receptores de adenosina (A1, A2a, A2b y A3); sin embargo el receptor A1 es el involucrado en la inhibición de la diferenciación neuronal como demostramos por PCR cuantitativa, Western Blot y en un ensayo de silenciamiento génico del receptor A1. Además, la activación del receptor A1 indujo una disminución de la expresión de genes relacionados con la neurogénesis como observamos en un análisis de expresión génica. El efecto inhibitorio de la activación del receptor A1 fue también confirmado en un modelo in vivo; de manera que observamos una reducción de la neurogénesis y un aumento de la astrogliogénesis en el bulbo olfatorio de ratas adultas tras la infusión intracerebroventricular del agonista del receptor A1 CPA. A su vez, el estudio de los mecanismos por los que la adenosina inhibe la neurogénesis y sostiene la astrogliogénesis demostraron la implicación de la IL10 y la activación de la ruta STAT3/Bmp2/Smad. Además, dado que la adenosina es liberada de forma masiva durante la isquemia cerebral, estudiamos el efecto del bloqueo del receptor A1 en un modelo de isquemia cerebral (oclusión transitoria de la arteria cerebral media). El antagonismo del receptor A1 produjo un aumento del número de nuevas neuronas (células positivas para DCX/BrdU o NeuN/BrdU) así como una reducción de nuevos astrocitos (células positivas para Thbs4/GFAP/BrdU) en la zona de penumbra isquémica. En definitiva, estos resultados sugieren que la activación del receptor A1 en isquemia puede ser un modulador de neurogénesis y astrogliogénesis

Hybrid superconductor-semiconductor systems for quantum technology

Superconducting quantum devices provide excellent connectivity and controllability while semiconductor spin qubits stand out with their long-lasting quantum coherence, fast control, and potential for miniaturization and scaling. In the last few years, remarkable progress has been made in combining superconducting circuits and semiconducting devices into hybrid quantum systems that benefit from the physical properties of both constituents. Superconducting cavities can mediate quantum-coherent coupling over long distances between electronic degrees of freedom such as the spin of individual electrons on a semiconductor chip and thus provide essential connectivity for a quantum device. Electron spins in semiconductor quantum dots have reached very long coherence times and allow for fast quantum gate operations with increasing fidelities. We summarize recent progress and theoretical models that describe superconducting-semiconducting hybrid quantum systems, explain the limitations of these systems, and describe different directions where future experiments and theory are headed.Comment: 5 pages, 3 figure

Input-output theory for spin-photon coupling in Si double quantum dots

The interaction of qubits via microwave frequency photons enables long-distance qubit-qubit coupling and facilitates the realization of a large-scale quantum processor. However, qubits based on electron spins in semiconductor quantum dots have proven challenging to couple to microwave photons. In this theoretical work we show that a sizable coupling for a single electron spin is possible via spin-charge hybridization using a magnetic field gradient in a silicon double quantum dot. Based on parameters already shown in recent experiments, we predict optimal working points to achieve a coherent spin-photon coupling, an essential ingredient for the generation of long-range entanglement. Furthermore, we employ input-output theory to identify observable signatures of spin-photon coupling in the cavity output field, which may provide guidance to the experimental search for strong coupling in such spin-photon systems and opens the way to cavity-based readout of the spin qubit