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Seigo Tarucha - One of the best experts on this subject based on the ideXlab platform.
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Transport properties of Two laterally coupled vertical quantum Dots in series with tunable inter-dot coupling
Applied Physics Letters, 2010Co-Authors: Tsuyoshi Hatano, Yasuhiro Tokura, Toshihiro Kubo, Shinichi Amaha, S. Teraoka, James A. Gupta, D. G. Austing, Seigo TaruchaAbstract:We describe the electronic properties of a double dot for which the lateral coupling between the Two vertical Dots can be controlled in-situ with a center gate voltage (Vc) and the current flows through the Two Dots in series. When Vc is large and positive, the Two Dots merge. As Vc is made less positive, Two Dots are formed whose coupling is reduced. We measure charging diagrams for positive and negative source-drain voltages in the weak coupling regime and observe current rectification due to the Pauli spin blockade when the hyperfine interaction between the electrons and the nuclei is suppressed.
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Single electron spin addressing by using photon-assisted-tunneling in a double quantum dot including a micro-magnet
Physica E: Low-dimensional Systems and Nanostructures, 2010Co-Authors: Yun-sok Shin, Toshiaki Obata, Michel Pioro-ladrière, Yasuhiro Tokura, R. Brunner, Toshihiro Kubo, K. Yoshida, Seigo TaruchaAbstract:In a numerical simulation we demonstrate spin readout by using photon assisted tunneling (PAT). We are using a realistic double quantum dot design including a micro-magnet. The micro-magnet generates different Zeeman fields between the Two Dots. If the photon frequency matches the energy difference of either the up-spin or the down-spin state between the Two Dots, the electron will be delocalized over the Two Dots by inter-dot PAT. We numerically simulate the micro-magnet induced stray field for various micro-magnet parameters and calculate the PAT spin readout performance.
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Dynamical polarization effect of nuclear spin bath dragged by electron spin resonance in double quantum dot integrated with micro-magnet
Journal of Physics: Conference Series, 2009Co-Authors: Toshiaki Obata, Yun-sok Shin, Michel Pioro-ladrière, Yasuhiro Tokura, R. Brunner, Toshihiro Kubo, K. Yoshida, Tomoyasu Taniyama, Seigo TaruchaAbstract:We studied on Overhauser shift of electron dipole spin resonance (EDSR) peaks by using a double quantum dot integrated with a micro-magnet. Two EDSR peaks are well resolved, reflecting electron spin flip events at different resonance conditions between Two Dots, which depend on the in-plane field at the Two Dots produced by a micro magnet. One of the Two peaks is significantly higher than the other and shows a larger Overhauser shift, indicating that an electron spin flip process local to the dot causes dynamical polarization of local nuclear spins to the same dot. After the nuclear spin polarization is saturated, we observed the decay of the Overhauser shift by repeatedly measuring the EDSR peak with a minimum microwave power. The decay time constant is much longer than by other groups. We discuss the possible reason for this difference.
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Negative Coulomb Drag in Parallel Quantum Wires Having Coupled Two Dots
AIP Conference Proceedings, 2005Co-Authors: Motonari Honda, Michael Stopa, Michihisa Yamamoto, Seigo TaruchaAbstract:We have fabricated capacitively coupled Two quantum wires having a series of quantum Dots to study Coulomb drag between the Two quantum wires. We have observed strong negative Coulomb drag when the electron transport through the Dots is in the tunneling regime for both wires. This indicates that electrons in one dot of the dive wire and holes in the other wire are strongly correlated to generate exciton‐like transport.
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Gate-voltage dependence of inter dot coupling and Aharanov-Bohm oscillation in laterally coupled vertical double dot
Physica E-low-dimensional Systems & Nanostructures, 2004Co-Authors: Tsuyoshi Hatano, Michael Stopa, Wataru Izumida, Tomohiro Yamaguchi, Takeshi Ota, Seigo TaruchaAbstract:Abstract We fabricated laterally coupled vertical double-dot devices and measured their electrical transport properties. In these devices, Two Dots are laterally coupled in parallel and connected to a common source, and drain contacts placed above, and below the Two Dots. The number of electrons in each dot and the inter-dot tunnel coupling are all tunable. The inter-dot tunnel coupling was changed between the weak and strong coupling regimes, as a function of gate voltage placed between Two Dots. When a magnetic field was applied parallel to the plane of the Two Dots and source/drain contacts, we observed oscillations of the current (Aharanov–Bohm oscillation) in the weak coupling regime (for a different device).
Pierre Jolicoeur - One of the best experts on this subject based on the ideXlab platform.
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Manipulating the shape of distance effects in visual curve tracing: further evidence for the zoom lens model.
Canadian journal of experimental psychology = Revue canadienne de psychologie experimentale, 1994Co-Authors: Peter A. Mccormick, Pierre JolicoeurAbstract:Abstract The time required to determine that Two Dots occur on the same cur ve in a visual display increases with increasing interdot curve distance. McCormick and Jolico eur (1991) presented a model of visual curve tracing in which a local operator with a varia ble size receptive field tracks the curve segment intervening the Two Dots. In this model, human r esponse time can be predicted by counting the number of shifts of the receptive field needed to t race the curve segment. The present study re - examined the predictive power of the zoom lens curve tracing model by selectively manipulating distractor proximity in four conditions and re gressing the predictions of the model on human response time. The model was compared with tw o other curve tracing models, pixel by pixel tracing, and Jolicoeur, Ullman and MacKay's (1991) bipartite receptive field operator. The results provided strong support for McC ormick and Jolicoeur's (1991) visual attention based zoom lens operator.Resume Le temps necessaire pour determiner l'appartenance de deux points a une meme courbe dans une presentation visuelle augmente avec la distance de la c ourbe entre les points. McCormick et Jolicoeur (1991) presente un modele de trace vis uel curviligne dans lequel un operateur, muni d'un champ recepteur de taille variabl e trace le segment de courbe entre les deux points. Dans ce modele, il est possible de pre voir le temps de reaction humaine en comptant le nombre de changements a porter au champ recepteur pour tracer le segment de courbe. La presente etude a reevalue la puissance previsible du modele de trace curviligne de la lentille zoom, par mani pulation selective de la proximite d'un facteur de distractivite en fonction de quatre co nditions, et par regression des predictions du modele sur le temps de reaction humaine. L es auteurs ont compare ce modele a deux autres modeles de trace curviligne, soit d'une part le trace pixel par pixel et, d'autre part, l'operateur de champ recep teur bipartite de Jolicoeur, Ullman et MacKay (1991). Les resultats ont solidement a ppuye l'operateur de l'attention visuelle axe sur lentille zoom de McCormick et Jolico eur (1991).The visual curve tracing task was first studied empirically by Jolicoeur, Ullman , and MacKay (1986). Subjects were presented with Two intertwiningbut nonintersecting curve s along with Two Dots. The subject's task was to determine, as quickly as possible, whether the Two Dots appeared on the same or on different curves. Jolicoeur et al. found that when the Two do ts were presented on the same curve, response time was a monotonically increasing function of the distance along the curve between the Two Dots. They concluded that when determining whether th e Two Dots occurred on the same curve, the intervening curve segment was traced visually.An unexpected result in the Jolicoeur et al. (1986) study was that of a non linear effect of curve distance on response time. McCormick and Jolicoeur (1991) examined this n onlinearity and found that the shape of the distance function varied according to stimulus c haracteristics and was not a property of visual curve tracing per se. They claimed that the varyin g proximity between the distractor curve (the curve that contained no Dots in the 'same' cur ve condition) and the target curve (the curve that contained the Two Dots in the 'same' curve cond ition) in the intertwining curves display may have allowed a local operator with a variable si zed processing field to move at different rates along the to - be - traced curve. McCormick an d Jolicoeur presented a curve tracing model, the zoom lens local operator, in which a curve is traced with a variable sized receptive field. They compared the predictions of this model w ith the predictions of Two other curve tracing models: pixel by pixel tracing and Jolico eur, Ullman, and MacKay's (1991) bipartite receptive field operator. These three models and the results of McCormick and Jolicoeur's analysis are described below. …
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Size invariance in curve tracing
Memory & cognition, 1991Co-Authors: Pierre Jolicoeur, Margaret IngletonAbstract:Subjects decided whether Two Dots were on the same curve or on different curves in patterns consisting of Two curves and Two Dots in displays that had an exposure duration of 200 msec or that remained in view until the subjects’ response. The overall size of the patterns was varied by a factor of Two. Furthermore, across experiments, we manipulated the predictability of the size of the pattern on a particular trial. On half of the trials, the Two Dots were on the same curve; across these trials, the distance between the Dots, along the curve, was manipulated systematically while the Euclidean distance between the Dots was held- constant. On the other half of the trials, the Two Dots were on different curves. The time to respondsame increased monotonically as curve distance between the Dots increased, suggesting that subjects mentally traced the curve. in order to perform the task. The absolute size of the pattern had little or no effect on the response times, indicating that it was curve distance relative to the overall pattern size, rather than absolute distance, that controlled response times. Furthermore, expectancies about pattern size had essentially no effect on performance. Taken together, the results suggest that the rate of tracing is determined by various stimulus properties that covary with the overall size of the pattern on which tracing takes place, such as the distance between the traced curve and nearby distractor curves, or the curvature of the traced curve.
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Predicting the shape of distance functions in curve tracing: Evidence for a zoom lens operator
Memory & cognition, 1991Co-Authors: Peter A. Mccormick, Pierre JolicoeurAbstract:Jolicoeur, Ullman, and MacKay (1986) showed that the time to confirm that Two Dots are on the same curve increases monotonically, but nonlinearly, as the curve distance between the Two Dots increases. These displays contained Two curves and Two Dots. On same trials, the Two Dots were on the same curve (target curve), while the other curve served as a foil (distractor curve). The monotonically increasing effects of curve distance on response times for same trials suggested that the intervening curve segment was traced. In the present investigation of the source of the nonlinearity in these distance functions, it was hypothesized that differences in the distractor curves may have allowed a curve tracing operator with zoom lens properties to widen its recep tive field while tracing parts of certain target curves. The wider receptive field may have allowed faster tracing over certain segments, owing to a reduced number of shifts required by the opera tor to scan the curve. The consequence of training certain segments of the curve more quickly than other segments of the curve would be a nonlinear effect of distance. A new set of stimuli was created for testing this hypothesis directly. Fairly linear distance effects were found for stimuli that contained a distractor curve that constrained the breadth of the postulated curve tracing operator, whereas stimuli that contained a distractor curve that could allow for a larger recep tive field yielded nonlinear distance functions. The results are compared with the predictions ofthree quantitative models: pixel-by-pixeltracing; Jolicoeur, Ullman, and MacKay's (1991)bipar tite operator; and a new zoom lens model, analogous to the zoom lens model of visual attention. The results were fit best by the latter model, in which tracing is accomplished by tracking the curve with a variably sized local operator. Ullman (1984) has suggested that the spatial relations between objects in a visual display are perceived through the implementation of visual routines that operate on early visual representations. A visual routineis an ordered as sembly of basic visual operations, such as covert and overt shifts of the processing focus, the indexing of locations for further processing, bounding surfaces for selective processing, boundary tracing, and the marking of surfaces and locations that have already been processed. In the present study, we are concerned with the boundary or curve tracing operation, which has been studied exten sively by Jolicoeur and his colleagues (Jolicoeur, 1988; Jolicoeur & Ingleton, 1991; Jolicoeur, Ullman, & MacKay, 1986, in press; McCormick & Jolicoeur, in press). The variable manipulated in these studies was whether or not Two Dots appeared on the same curve in a display consisting of Two or more nonintersecting curves. The results consistently showed monotonically in creasing response times as a function of the curve dis tance between the Two Dots, which has been taken as evi dence that the curves were traced, at a limited rate, in order to verify the spatial relation. This research was supported by a Natural Sciences and Engineering Research Council Grant awarded to P. Jolicoeur. The authors wish to thankJames Chumbley and three anonymous reviewers for their valu able comments on earlier versions of the manuscript. Correspondence
Tsuyoshi Hatano - One of the best experts on this subject based on the ideXlab platform.
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Transport properties of Two laterally coupled vertical quantum Dots in series with tunable inter-dot coupling
Applied Physics Letters, 2010Co-Authors: Tsuyoshi Hatano, Yasuhiro Tokura, Toshihiro Kubo, Shinichi Amaha, S. Teraoka, James A. Gupta, D. G. Austing, Seigo TaruchaAbstract:We describe the electronic properties of a double dot for which the lateral coupling between the Two vertical Dots can be controlled in-situ with a center gate voltage (Vc) and the current flows through the Two Dots in series. When Vc is large and positive, the Two Dots merge. As Vc is made less positive, Two Dots are formed whose coupling is reduced. We measure charging diagrams for positive and negative source-drain voltages in the weak coupling regime and observe current rectification due to the Pauli spin blockade when the hyperfine interaction between the electrons and the nuclei is suppressed.
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Gate-voltage dependence of inter dot coupling and Aharanov-Bohm oscillation in laterally coupled vertical double dot
Physica E-low-dimensional Systems & Nanostructures, 2004Co-Authors: Tsuyoshi Hatano, Michael Stopa, Wataru Izumida, Tomohiro Yamaguchi, Takeshi Ota, Seigo TaruchaAbstract:Abstract We fabricated laterally coupled vertical double-dot devices and measured their electrical transport properties. In these devices, Two Dots are laterally coupled in parallel and connected to a common source, and drain contacts placed above, and below the Two Dots. The number of electrons in each dot and the inter-dot tunnel coupling are all tunable. The inter-dot tunnel coupling was changed between the weak and strong coupling regimes, as a function of gate voltage placed between Two Dots. When a magnetic field was applied parallel to the plane of the Two Dots and source/drain contacts, we observed oscillations of the current (Aharanov–Bohm oscillation) in the weak coupling regime (for a different device).
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Single electron spectroscopy in a single pair of weakly coupled self-assembled InAs quantum Dots
Physica E-low-dimensional Systems & Nanostructures, 2004Co-Authors: Takeshi Ota, Tsuyoshi Hatano, Seigo Tarucha, Keiji Ono, H.z. Song, Yoshiaki Nakata, T. Miyazawa, Toshio Ohshima, Naoki YokoyamaAbstract:Abstract Using a single electron transistor containing a single pair of weakly coupled self-assembled InAs quantum Dots, we have studied the transport properties of elastic and inelastic single electron tunneling. We found a series of Coulomb diamonds above pinch off voltage and, below it, characteristic irregular structures in the current vs. source-drain voltage and gate voltage, consisting of “vertical lines” and “kinks”. Based on a simple calculation, the vertical lines are assigned to elastic tunneling between aligned states of the Two Dots. The kinks come from change of electron number in the Dots, observed in the inelastic tunneling regime through off-resonant states in the Two Dots.
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Delocalization energy probed by asymmetry of Coulomb diamond in double dot system
Superlattices and Microstructures, 2003Co-Authors: Tsuyoshi Hatano, Tomohiro Yamaguchi, Takeshi Ota, Micheal Stopa, Kazumasa Yamada, Seigo TaruchaAbstract:Abstract We present results of measurements of the I–V characteristics of a unique parallel double dot where the current flows vertically but the coupling is lateral. Probed by asymmetry of Coulomb diamonds in the standard double-dot honeycomb stability diagram, we are able to discern in what sequence electrons are added in the Two Dots.
Yasuhiro Tokura - One of the best experts on this subject based on the ideXlab platform.
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Transport properties of Two laterally coupled vertical quantum Dots in series with tunable inter-dot coupling
Applied Physics Letters, 2010Co-Authors: Tsuyoshi Hatano, Yasuhiro Tokura, Toshihiro Kubo, Shinichi Amaha, S. Teraoka, James A. Gupta, D. G. Austing, Seigo TaruchaAbstract:We describe the electronic properties of a double dot for which the lateral coupling between the Two vertical Dots can be controlled in-situ with a center gate voltage (Vc) and the current flows through the Two Dots in series. When Vc is large and positive, the Two Dots merge. As Vc is made less positive, Two Dots are formed whose coupling is reduced. We measure charging diagrams for positive and negative source-drain voltages in the weak coupling regime and observe current rectification due to the Pauli spin blockade when the hyperfine interaction between the electrons and the nuclei is suppressed.
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Single electron spin addressing by using photon-assisted-tunneling in a double quantum dot including a micro-magnet
Physica E: Low-dimensional Systems and Nanostructures, 2010Co-Authors: Yun-sok Shin, Toshiaki Obata, Michel Pioro-ladrière, Yasuhiro Tokura, R. Brunner, Toshihiro Kubo, K. Yoshida, Seigo TaruchaAbstract:In a numerical simulation we demonstrate spin readout by using photon assisted tunneling (PAT). We are using a realistic double quantum dot design including a micro-magnet. The micro-magnet generates different Zeeman fields between the Two Dots. If the photon frequency matches the energy difference of either the up-spin or the down-spin state between the Two Dots, the electron will be delocalized over the Two Dots by inter-dot PAT. We numerically simulate the micro-magnet induced stray field for various micro-magnet parameters and calculate the PAT spin readout performance.
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Dynamical polarization effect of nuclear spin bath dragged by electron spin resonance in double quantum dot integrated with micro-magnet
Journal of Physics: Conference Series, 2009Co-Authors: Toshiaki Obata, Yun-sok Shin, Michel Pioro-ladrière, Yasuhiro Tokura, R. Brunner, Toshihiro Kubo, K. Yoshida, Tomoyasu Taniyama, Seigo TaruchaAbstract:We studied on Overhauser shift of electron dipole spin resonance (EDSR) peaks by using a double quantum dot integrated with a micro-magnet. Two EDSR peaks are well resolved, reflecting electron spin flip events at different resonance conditions between Two Dots, which depend on the in-plane field at the Two Dots produced by a micro magnet. One of the Two peaks is significantly higher than the other and shows a larger Overhauser shift, indicating that an electron spin flip process local to the dot causes dynamical polarization of local nuclear spins to the same dot. After the nuclear spin polarization is saturated, we observed the decay of the Overhauser shift by repeatedly measuring the EDSR peak with a minimum microwave power. The decay time constant is much longer than by other groups. We discuss the possible reason for this difference.
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Angular momentum selectivity in tunneling between Two quantum Dots
Physica B-condensed Matter, 2001Co-Authors: Kanta Ono, Yasuhiro Tokura, David Guy Austing, Seigo TaruchaAbstract:Abstract We measure the current–voltage characteristics of a single-electron transistor containing Two vertically coupled circular-disk-shaped quantum Dots in a magnetic field applied perpendicular to the disks, and observe current peaks associated with elastic tunneling through the Two Dots. The magnetic field dependence of the peak positions follows that of the Fock–Darwin states, and the peak height becomes smaller as the difference in angular momentum of the states of the Two Dots increase. We use a sequential tunneling model to account for this result.
Toshihiro Kubo - One of the best experts on this subject based on the ideXlab platform.
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Transport properties of Two laterally coupled vertical quantum Dots in series with tunable inter-dot coupling
Applied Physics Letters, 2010Co-Authors: Tsuyoshi Hatano, Yasuhiro Tokura, Toshihiro Kubo, Shinichi Amaha, S. Teraoka, James A. Gupta, D. G. Austing, Seigo TaruchaAbstract:We describe the electronic properties of a double dot for which the lateral coupling between the Two vertical Dots can be controlled in-situ with a center gate voltage (Vc) and the current flows through the Two Dots in series. When Vc is large and positive, the Two Dots merge. As Vc is made less positive, Two Dots are formed whose coupling is reduced. We measure charging diagrams for positive and negative source-drain voltages in the weak coupling regime and observe current rectification due to the Pauli spin blockade when the hyperfine interaction between the electrons and the nuclei is suppressed.
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Single electron spin addressing by using photon-assisted-tunneling in a double quantum dot including a micro-magnet
Physica E: Low-dimensional Systems and Nanostructures, 2010Co-Authors: Yun-sok Shin, Toshiaki Obata, Michel Pioro-ladrière, Yasuhiro Tokura, R. Brunner, Toshihiro Kubo, K. Yoshida, Seigo TaruchaAbstract:In a numerical simulation we demonstrate spin readout by using photon assisted tunneling (PAT). We are using a realistic double quantum dot design including a micro-magnet. The micro-magnet generates different Zeeman fields between the Two Dots. If the photon frequency matches the energy difference of either the up-spin or the down-spin state between the Two Dots, the electron will be delocalized over the Two Dots by inter-dot PAT. We numerically simulate the micro-magnet induced stray field for various micro-magnet parameters and calculate the PAT spin readout performance.
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Dynamical polarization effect of nuclear spin bath dragged by electron spin resonance in double quantum dot integrated with micro-magnet
Journal of Physics: Conference Series, 2009Co-Authors: Toshiaki Obata, Yun-sok Shin, Michel Pioro-ladrière, Yasuhiro Tokura, R. Brunner, Toshihiro Kubo, K. Yoshida, Tomoyasu Taniyama, Seigo TaruchaAbstract:We studied on Overhauser shift of electron dipole spin resonance (EDSR) peaks by using a double quantum dot integrated with a micro-magnet. Two EDSR peaks are well resolved, reflecting electron spin flip events at different resonance conditions between Two Dots, which depend on the in-plane field at the Two Dots produced by a micro magnet. One of the Two peaks is significantly higher than the other and shows a larger Overhauser shift, indicating that an electron spin flip process local to the dot causes dynamical polarization of local nuclear spins to the same dot. After the nuclear spin polarization is saturated, we observed the decay of the Overhauser shift by repeatedly measuring the EDSR peak with a minimum microwave power. The decay time constant is much longer than by other groups. We discuss the possible reason for this difference.
