Dark Bell states in tunnel-coupled spin qubits

We investigate the dynamical purification of maximally entangled electron states by transport through coupled quantum dots. Under resonant ac driving and coherent tunneling, even-parity Bell states perform Rabi oscillations that decouple from the environment, leading to a dark state. The two electrons remain spatially separated, one in each quantum dot. We propose configurations where this effect will prove as antiresonances in transport spectroscopy experiments.Comment: 5 pages, 4 figures + supplementary information. Published versio

Control of Spin Blockade by AC Magnetic Fields in Triple Quantum Dots

We analyze coherent spin phenomena in triple quantum dots in triangular configuration under crossed DC and AC magnetic fields. In particular, we discuss the interplay between Aharonov-Bohm current oscillations, coherent electron trapping and spin blockade under electron spin resonance conditions. We demonstrate that, for certain field frequencies, AC magnetic fields induce an antiresonant behavior in the current, allowing for both removal and restoration of entangled spin blockaded states by tuning the AC field frequency. Our theoretical predictions indicate how to manipulate spin qubits in a triangular quantum dot array.Comment: 4 pages, 5 figure

Coupled Landau-Zener-Stuckelberg Quantum Dot Interferometers

We investigate the interplay between long-range and direct photon-assisted transport in a triple quantum dot chain where local ac voltages are applied to the outer dots. We propose the phase difference between the two ac voltages as an external parameter, which can be easily tuned to manipulate the current characteristics. For gate voltages in phase opposition we find quantum destructive interferences analogous to the interferences in closed-loop undriven triple dots. As the voltages oscillate in phase, interferences between multiple paths give rise to dark states. Those totally cancel the current, and could be experimentally resolved.Comment: 6 pages, 4 figure

Superexchange blockade in triple quantum dots

We propose the interaction of two electrons in a triple quantum dot as a minimal system to control long range superexchange transitions. These are probed by transport spectroscopy. Narrow resonances appear indicating the transfer of charge from one side of the sample to the other with the central one being occupied only virtually. We predict that two different intermediate states establish the two arms of a one dimensional interferometer. Configurations of destructive interference of the two superexchage trajectories totally block the current through the system. We emphasize the role of spin correlations giving rise to lifetime-enhanced resonances.Comment: 5 pages, 4 figures. Published versio

Spin filtering through excited states in double quantum dot pumps

Recently it has been shown that ac-driven double quantum dots can act as spin pumps and spin filters. By calculating the current through the system for each spin polarization, by means of the time evolution of the reduced density matrix in the sequential tunneling regime (Born-Markov approximation), we demonstrate that the spin polarization of the current can be controlled by tuning the parameters (amplitude and frequency) of the ac field. Importantly, the pumped current as a function of the applied frequency presents a series of peaks which are uniquely associated with a definite spin polarization. We discuss how excited states participating in the current allow the system to behave as a bipolar spin filter by tuning the ac frequency and intensity. We also discuss spin relaxation and decoherence effects in the pumped current and show that measuring the width of the current vs frequency peaks allows to determine the spin decoherence time $T_{2}$.Comment: 10 pages. 5 figure

Electron Bunching in Stacks of Coupled Quantum Dots

We study the transport properties of two double quantum dots in a parallel arrangement at temperatures of a few Kelvin. Thereby, we show that decoherence entailed by the substrate phonons affects the shot noise. For asymmetric coupling between the dots and the respective lead, the current noise is sub-Poissonian for resonant tunneling, but super-Poissonian in the vicinity of the resonances. Our results indicate that phonon emission and absorption is responsible for the shot noise enhancement. The observed asymmetry of the peaks at low temperatures stems from spontaneous emission.Comment: 4 pages, 5 figures. Published versio

An analysis of second life in foreign language learning and teaching: exploring its potential

XVIII Jornades de Foment de la Investigació de la Facultat de Ciències Humanes i Socials (Any 2013)The use of Information and Communication Technologies (ICTs) in language learning and teaching has greatly increased in the last decade. Among the different technological tools used in the learning process, virtual worlds have gained popularity among educators and students (e.g. Warburton, 2009; Wang & Burton, 2012; Zhang, 2012; Duncan et al., 2012). This article explores the different possibilities the virtual world Second Life (SL) offers in the language learning process. SL is an online virtual world where residents all over the globe can interact through their avatars by which they can collaborate and learn in an experimental way. This paper offers a theoretical approach about the potential of SL in foreign language education. Firstly, it explores the use of this platform in education, explaining its origins, evolution and current changes. Secondly, it will focus on the advantages and disadvantages of the use of this virtual world for learning languages, paying special attention to the different learning environments, the students’ motivation, and the educational activities amongst others. This paper will conclude with a section of pedagogical implications in which an activity will be proposed to show the different implications of SL in a foreign language classroom. Students will have to work on four different activities that will be based on one of the main four language skills that are established by the Common European Framework of Reference (CEFR): writing, speaking, listening and reading. After explaining the activity, special attention will be paid to the strengths and weaknesses of this specific task

A microscopy technique based on bio-impedance sensors

It is proposed a microscopy for cell culture applications based on impedance sensors. The imagined signals are measured with the Electrical Cell-Substrate Spectroscopy (ECIS) technique, by identifying the cell area. The proposed microscopy allows real-time monitoring inside the incubator, reducing the contamination risk by human manipulation. It requires specific circuits for impedance measurements, a two-dimensional sensor array (pixels), and employing electrical models to decode efficiently the measured signals. Analogue Hardware Description Language (AHDL) circuits for cell-microelectrode enables the use of geometrical and technological data into the system design flow. A study case with 8x8 sensor array is reported, illustrating the evolution and power of the proposed image acquisition.Junta de Andalucía P0-TIC-538