Controlled dephasing in single-dot Aharonov-Bohm interferometers

We study the Fano effect and the visibility of the Aharonov-Bohm oscillations for a mesoscopic interferometer with an embedded quantum dot in the presence of a nearby second dot. When the electron-electron interaction between the two dots is considered the nearby dot acts as a charge detector. We compute the currents through the interferometer and detector within the Keldysh formalism and the self-energy of the non-equilibrium Green functions is found up to the second order in the interaction strength. The current formula contains a correction to the Landauer-B\"{uttiker} formula. Its contribution to transport and dephasing is discussed. As the bias applied on the detector is increased, the amplitude of both the Fano resonance and Aharonov-Bohm oscillations are considerably reduced due to controlled dephasing. This result is explained by analyzing the behavior of the imaginary part of the self-energy as a function of energy and bias. We investigate as well the role of the ring-dot coupling. Our theoretical results are consistent to the experimental observation of Buks {\it et al.} [Nature {\bf 391}, 871 (1998)].Comment: 24 pages, 8 figure

Resonant and coherent transport through Aharonov-Bohm interferometers with coupled quantum dots

A detailed description of the tunneling processes within Aharonov-Bohm (AB) rings containing two-dimensional quantum dots is presented. We show that the electronic propagation through the interferometer is controlled by the spectral properties of the embedded dots and by their coupling with the ring. The transmittance of the interferometer is computed by the Landauer-B\"uttiker formula. Numerical results are presented for an AB interferometer containing two coupled dots. The charging diagrams for a double-dot interferometer and the Aharonov Bohm oscillations are obtained, in agreement with the recent experimental results of Holleitner {\it et al}. [Phys. Rev. Lett. {\bf 87}, 256802 (2001)] We identify conditions in which the system shows Fano line shapes. The direction of the asymetric tail depends on the capacitive coupling and on the magnetic field. We discuss our results in connection with the experiments of Kobayashi {\it et al} [Phys. Rev. Lett. {\bf 88}, 256806 (2002)] in the case of a single dot.Comment: 30 pages, 12 figure

Light-hole exciton mixing and dynamics in Mn-doped quantum dots

We investigate theoretically the spectral and dynamical effects of the short-range exchange interaction between a single manganese (Mn) atom hosted by cylindrical CdTe quantum dots and its light-hole excitons or biexcitons. Our approach is based on the Kohn-Luttinger KP theory and configuration interaction method, the dynamics of the system in the presence of intraband relaxation being derived from the von Neumann-Lindblad equation. The complex structure of the light-hole exciton absorption spectrum reveals the exchange-induced exciton mixing and depends strongly on the Mn position. In particular, if the Mn atom is closer to the edges of the cylinder the bright and dark light-hole excitons are mixed by the hole-Mn exchange alone. Consequently, their populations exhibit exchange-induced Rabi oscillations which can be viewed as optical signatures of light-hole spin reversal. Similar results are obtained for mixed biexcitons, in this case the exchange-induced Rabi oscillations being damped by the intraband hole relaxation processes. The effect of light-hole heavy-hole mixing is also discussed.Comment: 9 pages, 7 figures, to appear in Phys. Rev.

Mesoscopic Fano Effect in a spin splitter with a side-coupled quantum dot

Cataloged from PDF version of article.We investigate the interplay between the spin interference and the Fano effect in a three-lead mesoscopic ring with a side-coupled quantum dot (QD). A uniform Rashba spin-orbit coupling and a perpendicular magnetic field are tuned such that the ring operates as a spin splitter in the absence of the QD: one lead is used to inject unpolarized electrons and the remaining (output) leads collect almost polarized spin currents. By applying a gate potential to the quantum dot a pair of spin-split levels sweeps the bias window and leads to Fano interference. The steady-state spin and charge currents in the leads are calculated for a finite bias applied across the ring via the non-equilibrium Green's function formalism. When the QD levels participate to transport we find that the spin currents exhibit peaks and dips whereas the charge currents present Fano lineshapes. The location of the side-coupled quantum dot and the spin splitting of its levels also affect the interference and the output currents. The opposite response of output currents to the variation of the gate potential allows one to use this system as a single parameter current switch. We also analyze the dependence of the splitter efficiency on the spin splitting on the QD. (C) 2012 Elsevier B.V. All rights reserved

Quantum turnstile operation of single-molecule magnets

The time-dependent transport through single-molecule magnets coupled to magnetic or non-magnetic electrodes is studied in the framework of the generalized master equation method. We investigate the transient regime induced by the periodic switching of the source and drain contacts. If the electrodes have opposite magnetizations the quantum turnstile operation allows the stepwise writing of intermediate excited states. In turn, the transient currents provide a way to read these states. Within our approach we take into account both the uniaxial and transverse anisotropy. The latter may induce additional quantum tunneling processes which affect the efficiency of the proposed read-and-write scheme. An equally weighted mixture of molecular spin states can be prepared if one of the electrodes is ferromagnetic.Comment: 19 pages, 6 figure

Enhancement of linear and nonlinear optical properties of deoxyribonucleic acid-silica thin films doped with rhodamine

In this work, we present the linear and nonlinear optical properties of DNA as functional material, incorporated into a silica material matrix with rhodamine organic dye. We observed that even low concentration of DNA affects the aggregate behavior of the dyes in silica films. The samples with DNA showed higher transmittance and fluorescence efficiency. Moreover, the presence of DNA has been found to significantly enhance the nonlinear optical response of the systems. In this way, we prove that silica materials can provide suitable matrices for hybridization with functional molecules and can be utilized as active optical waveguide materials with enhanced nonlinear optical properties

Coherent manipulation of charge qubits in double quantum dots

The coherent time evolution of electrons in double quantum dots induced by fast bias-voltage switches is studied theoretically. As it was shown experimentally, such driven double quantum dots are potential devices for controlled manipulation of charge qubits. By numerically solving a quantum master equation we obtain the energy- and time-resolved electron transfer through the device which resembles the measured data. The observed oscillations are found to depend on the level offset of the two dots during the manipulation and, most surprisingly, also the on initialization stage. By means of an analytical expression, obtained from a large-bias model, we can understand the prominent features of these oscillations seen in both the experimental data and the numerical results. These findings strengthen the common interpretation in terms of a coherent transfer of electrons between the dots.Comment: 18 pages, 4 figure

Exploring the Consequences of Nonbelieved Memories in the DRM Paradigm

In the current experiments, we attempted to elicit nonbelieved memories (NBMs) using the Deese/Roediger–McDermott (DRM) false memory paradigm. Furthermore, by using this approach, we explored the consequences of nonbelieved true and false memories. In Experiments 1 and 2, participants received several DRM wordlists and were presented with a recognition task. After the recognition task, participants’ statements were contradicted by giving them feedback about true and false items. In this way, we succeeded in eliciting nonbelieved true and false memories. In Experiment 2, participants were also involved in a modified perceptual closure task after receiving belief-relevant feedback. In this task, participants received degraded visual representations of words (e.g., false and true) that became clearer over time. Participants had to identify them as fast as possible. We also measured dissociation, compliance, and social desirability. We found that undermining belief had contrasting consequences for true and false memories. That is, nonbelieved true memories were identified more slowly whereas nonbelieved false memories were identified more quickly. We did not find any relation between our individual differences measures and the formation of NBMs