100 research outputs found
Laser phase modulation approaches towards ensemble quantum computing
Selective control of decoherence is demonstrated for a multilevel system by
generalizing the instantaneous phase of any chirped pulse as individual terms
of a Taylor series expansion. In the case of a simple two-level system, all odd
terms in the series lead to population inversion while the even terms lead to
self-induced transparency. These results also hold for multiphoton transitions
that do not have any lower-order photon resonance or any intermediate virtual
state dynamics within the laser pulse-width. Such results form the basis of a
robustly implementable CNOT gate.Comment: 10 pages, 4 figures, PRL (accepted
Observation of coherent transients in ultrashort chirped excitation of an undamped two-level system
The effects of Coherent excitation of a two level system with a linearly
chirped pulse are studied theoretically and experimentally (in Rb (5s - 5p)) in
the low field regime. The Coherent Transients are measured directly on the
excited state population on an ultrashort time scale. A sharp step corresponds
to the passage through resonance. It is followed by oscillations resulting from
interferences between off-resonant and resonant contributions. We finally show
the equivalence between this experiment and Fresnel diffraction by a sharp
edge.Comment: 4 pages, 4 figures, to appear in PR
Coherent Control of Multiphoton Transitions with Femtosecond pulse shaping
We explore the effects of ultrafast shaped pulses for two-level systems that
do not have a single photon resonance by developing a multiphoton
density-matrix approach. We take advantage of the fact that the dynamics of the
intermediate virtual states are absent within our laser pulse timescales. Under
these conditions, the multiphoton results are similar to the single photon and
that it is possible to extend the single photon coherent control ideas to
develop multiphoton coherent control.Comment: 13 pages, 7 figures. submitted to PR
Attention to Speech-Accompanying Gestures: Eye Movements and Information Uptake
There is growing evidence that addressees in interaction integrate the semantic information conveyed by speakers’ gestures. Little is known, however, about whether and how addressees’ attention to gestures and the integration of gestural information can be modulated. This study examines the influence of a social factor (speakers’ gaze to their own gestures), and two physical factors (the gesture’s location in gesture space and gestural holds) on addressees’ overt visual attention to gestures (direct fixations of gestures) and their uptake of gestural information. It also examines the relationship between gaze and uptake. The results indicate that addressees’ overt visual attention to gestures is affected both by speakers’ gaze and holds but for different reasons, whereas location in space plays no role. Addressees’ uptake of gesture information is only influenced by speakers’ gaze. There is little evidence of a direct relationship between addressees’ direct fixations of gestures and their uptake
Does Sleep Improve Your Grammar? : Preferential Consolidation of Arbitrary Components of New Linguistic Knowledge
We examined the role of sleep-related memory consolidation processes in learning new form-meaning mappings. Specifically, we examined a Complementary Learning Systems account, which implies that sleep-related consolidation should be more beneficial for new hippocampally dependent arbitrary mappings (e.g. new vocabulary items) relative to new systematic mappings (e.g. grammatical regularities), which can be better encoded neocortically. The hypothesis was tested using a novel language with an artificial grammatical gender system. Stem-referent mappings implemented arbitrary aspects of the new language, and determiner/suffix+natural gender mappings implemented systematic aspects (e.g. tib scoiffesh + ballerina, tib mofeem + bride; ked jorool + cowboy, ked heefaff + priest). Importantly, the determiner-gender and the suffix-gender mappings varied in complexity and salience, thus providing a range of opportunities to detect beneficial effects of sleep for this type of mapping. Participants were trained on the new language using a word-picture matching task, and were tested after a 2-hour delay which included sleep or wakefulness. Participants in the sleep group outperformed participants in the wake group on tests assessing memory for the arbitrary aspects of the new mappings (individual vocabulary items), whereas we saw no evidence of a sleep benefit in any of the tests assessing memory for the systematic aspects of the new mappings: Participants in both groups extracted the salient determiner-natural gender mapping, but not the more complex suffix-natural gender mapping. The data support the predictions of the complementary systems account and highlight the importance of the arbitrariness/systematicity dimension in the consolidation process for declarative memories
How What We See and What We Know Influence Iconic Gesture Production
In face-to-face communication, speakers typically integrate information acquired through different sources, including what they see and what they know, into their communicative messages. In this study, we asked how these different input sources influence the frequency and type of iconic gestures produced by speakers during a communication task, under two degrees of task complexity. Specifically, we investigated whether speakers gestured differently when they had to describe an object presented to them as an image or as a written word (input modality) and, additionally, when they were allowed to explicitly name the object or not (task complexity). Our results show that speakers produced more gestures when they attended to a picture. Further, speakers more often gesturally depicted shape information when attended to an image, and they demonstrated the function of an object more often when they attended to a word. However, when we increased the complexity of the task by forbidding speakers to name the target objects, these patterns disappeared, suggesting that speakers may have strategically adapted their use of iconic strategies to better meet the task’s goals. Our study also revealed (independent) effects of object manipulability on the type of gestures produced by speakers and, in general, it highlighted a predominance of molding and handling gestures. These gestures may reflect stronger motoric and haptic simulations, lending support to activation-based gesture production accounts
Photoconductivity of organic semiconductor polymers studied by time-resolved THz-TDS
This study employs optical-pump terahertzprobe time-domain spectroscopy to measure relative carrier mobilities of semiconductor organic polymer films of poly-3-hexylthiophene (P3HT) and poly(2,5-bis(3-tetradecylthiophen-2-yi) thieno[3,2-b]thiophene) (PBTTT) polymers and these results directly correlate to recently reported electrical device mobility measurements.. An approximately four-fold increase in mobility of P3HT is observed with molecular weight increase from c.a. 18 kD to 150 kD where the intrinsic film mobility saturates for molecular weight > 70 kD. The decay dynamics studies of these polymers showed almost no dependence on the molecular weight of the polymer. The studies also showed an order of magnitude increase in mobility between as cast P3HT films and annealed PBTTT films supporting a strong conjugation length effect. We also measured the mobility dependence on the film quality that is affected by regularity of the polymer, dispersing solvent, electron acceptor traps, and other film growth related parameters relevant to device manufacturing
Intrinsic Photoconductivity of P3HT films Measured by Time-Resolved THz spectroscopy
Intrinsic photoconductivities of P3HT polymers were measured and compared by using optical pump-THz probe spectroscopy. The charge carrier mobility shows a clear dependence on the molecular weight and dispersion index of the polymers
Terahertz mobility measurements on poly-3-hexylthiophene films: Device comparison, molecular weight, and film processing effects
We directly compare relative carrier mobilities in semiconducting organic polymer films measured using noncontact optical pump terahertz (THz) probe spectroscopy to those reported in electrical device studies. Relative transient signal amplitude measurements of photoinjected carrier mobility as a function of poly-3-hexylthiophene (P3HT) molecular weight correlate directly with electrical device test values, indicating that the THz method shows promise as a rapid material screening approach. We also present measurements on P3HT conducting films as a function of structural regularity, dispersing solvent, addition of C-60 electron traps, sample temperature, and other growth parameters relevant to device manufacture. (c) 2008 American Institute of Physics
Photoconductivity of P3HT films measured by time-resolved THz spectroscopy
Photoconductivities of P3HT polymer films varying in molecular weight were directly measured and compared using optical pump-THz probe spectroscopy. Conductivities of P3HT polymers depend on the polymer length, ring orientation regularity and film morphology. © 2007 Optical Society of America
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