Controlled dephasing of a quantum dot in the Kondo regime

Kondo correlation in a spin polarized quantum dot (QD) results from the dynamical formation of a spin singlet between the dot's net spin and a Kondo cloud of electrons in the leads, leading to enhanced coherent transport through the QD. We demonstrate here significant dephasing of such transport by coupling the QD and its leads to potential fluctuations in a near by 'potential detector'. The qualitative dephasing is similar to that of a QD in the Coulomb Blockade regime in spite of the fact that the mechanism of transport is quite different. A much stronger than expected suppression of coherent transport is measured, suggesting that dephasing is induced mostly in the 'Kondo cloud' of electrons within the leads and not in the QD.Comment: to be published in PR

Dephasing and Measurement Efficiency via a Quantum Dot Detector

We study charge detection and controlled dephasing of a mesoscopic system via a quantum dot detector (QDD), where the mesoscopic system and the QDD are capacitively coupled. The QDD is considered to have coherent resonant tunnelling via a single level. It is found that the dephasing rate is proportional to the square of the conductance of the QDD for the Breit-Wigner model, showing that the dephasing is completely different from the shot noise of the detector. The measurement rate, on the other hand, shows a dip near the resonance. Our findings are peculiar especially for a symmetric detector in the following aspect: The dephasing rate is maximum at resonance of the QDD where the detector conductance is insensitive to the charge state of the mesoscopic system. As a result, the efficiency of the detector shows a dip and vanishes at resonance, in contrast to the single-channel symmetric non-resonant detector that has always a maximum efficiency. We find that this difference originates from a very general property of the scattering matrix: The abrupt phase change exists in the scattering amplitudes in the presence of the symmetry, which is insensitive to the detector current but {\em stores} the information of the quantum state of the mesoscopic system.Comment: 7 pages, 3 figure

Crossover from mesoscopic to universal phase for electron transmission in quantum dots

Measuring phase in coherent electron systems (mesoscopic systems) provides ample information not easily revealed by conductance measurements. Phase measurements in relatively large quantum dots (QDs) recently demonstrated a universal like phase evolution independent of dot size, shape, and occupancy. Explicitly, in Coulomb blockaded QDs the transmission phase increased monotonically by pi throughout each conductance peak, thereafter, in the conductance valleys the phase returned sharply to its base value. Expected mesoscopic features in the phase, related to spin degeneracy or to exchange effects, were never observed. Presently, there is no satisfactory full explanation for the observed phase universality. Unfortunately, the phase in a few-electron QDs, where it can be better understood was never measured. Here we report on such measurements on a small QD that occupy only 1-20 electrons. Such dot was embedded in one arm of a two path electron interferometer, with an electron counter near the dot. Unlike the repetitive behavior found in larger dots we found now mesoscopic features for dot occupation of less than some 10 electrons. An unexpected feature in this regime is a clear observation of the occupation of two different orbital states by the first two electrons - contrary to the recent publications. As the occupation increased the phase evolved and turned universal like for some 14 electrons and higher. The present measurements allowed us to determine level occupancy and parity. More importantly, they suggest that QDs go through a phase transition, from mesoscopic to universal like behavior, as the occupancy increases. These measurements help in singling out potential few theoretical models among the many proposed.Comment: 12 pages, 6 figure

Fano Effect in a Few-Electron Quantum Dot

We have studied the Fano effect in a few-electron quantum dot side-coupled to a quantum wire. The conductance of the wire, which shows an ordinal staircase-like quantization without the dot, is modified through the interference (the Fano effect) and the charging effects. These effects are utilized to verify the exhaustion of electrons in the dot. The "addition energy spectrum" of the dot shows a shell structure, indicating that the electron confinement potential is fairly circular. A rapid sign inversion of the Fano parameter on the first conductance plateau with the change of the wire gate voltage has been observed, and explained by introducing a finite width of dot-wire coupling.Comment: 11 pages, 7 figure

Controlled Dephasing of Electrons by Non-Gaussian Shot Noise

In a 'controlled dephasing' experiment [1-3], an interferometer loses its coherence due to entanglement with a controlled quantum system ('which path' detector). In experiments that were conducted thus far in mesoscopic systems only partial dephasing was achieved. This was due to weak interactions between many detector electrons and the interfering electron, resulting in a Gaussian phase randomizing process [4-10]. Here, we report the opposite extreme: a complete destruction of the interference via strong phase randomization only by a few electrons in the detector. The realization was based on interfering edge channels (in the integer quantum Hall effect regime, filling factor 2) in a Mach-Zehnder electronic interferometer, with an inner edge channel serving as a detector. Unexpectedly, the visibility quenched in a periodic lobe-type form as the detector current increased; namely, it periodically decreased as the detector current, and thus the detector's efficiency, increased. Moreover, the visibility had a V-shape dependence on the partitioning of the detector current, and not the expected dependence on the second moment of the shot noise, T(1-T), with T the partitioning. We ascribe these unexpected features to the strong detector-interferometer coupling, allowing only 1-3 electrons in the detector to fully dephase the interfering electron. Consequently, in this work we explored the non-Gaussian nature of noise [11], namely, the direct effect of the shot noise full counting statistics [12-15].Comment: 14 pages, 4 figure

Nonequilibrium transport in quantum impurity models: Exact path integral simulations

We simulate the nonequilibrium dynamics of two generic many-body quantum impurity models by employing the recently developed iterative influence-functional path integral method [Phys. Rev. B {\bf 82}, 205323 (2010)]. This general approach is presented here in the context of quantum transport in molecular electronic junctions. Models of particular interest include the single impurity Anderson model and the related spinless two-state Anderson dot. In both cases we study the time evolution of the dot occupation and the current characteristics at finite temperature. A comparison to mean-field results is presented, when applicable

Dynamical stabilization and time in open quantum systems

The meaning of time in an open quantum system is considered under the assumption that both, system and environment, are quantum mechanical objects. The Hamilton operator of the system is non-Hermitian. Its imaginary part is the time operator. As a rule, time and energy vary continuously when controlled by a parameter. At high level density, where many states avoid crossing, a dynamical phase transition takes place in the system under the influence of the environment. It causes a dynamical stabilization of the system what can be seen in many different experimental data. Due to this effect, time is bounded from below: the decay widths (inverse proportional to the lifetimes of the states) do not increase limitless. The dynamical stabilization is an irreversible process.Comment: Contribution to the Special Issue "Quantum Physics with Non-Hermitian Operators: Theory and Experiment", Fortschritte der Physik - Progress of Physic

Avpr1a variant associated with preschoolers' lower altruistic behavior

10.1371/journal.pone.0025274PLoS ONE69

Genetics of Nurture: A Test of the Hypothesis That Parents’ Genetics Predict Their Observed Caregiving

Twin studies have documented that parenting behavior is partly heritable, but it is unclear how parents' genetics shape their caregiving. Using tools of molecular genetics, the present study investigated this process by testing hypotheses about associations between a genome-wide polygenic score for educational attainment and parental caregiving in 702 members of the Dunedin Study, a population-representative birth cohort. Data have been prospectively collected from when Study members were born through to midlife, and include assessments of the caregiving they provided once they became parents. Results showed that parents' polygenic scores predicted warm, sensitive, and stimulating caregiving, both in personal interactions with their young children (as captured on video) and through the home environments they created for their families (as observed by home visitors). The magnitude of this effect was small. Polygenic-score associations were independent of well-established predictors of parenting, such as parents' own childhood experiences of parenting and the age at which they became parents. Polygenic-score associations were mediated by parents' early-emerging cognitive abilities and self-control skills. Findings have implications for theory and research about genetic influences on caregiving and child development. (PsycINFO Database Record (c) 2019 APA, all rights reserved)

Physiological Correlates of Volunteering

We review research on physiological correlates of volunteering, a neglected but promising research field. Some of these correlates seem to be causal factors influencing volunteering. Volunteers tend to have better physical health, both self-reported and expert-assessed, better mental health, and perform better on cognitive tasks. Research thus far has rarely examined neurological, neurochemical, hormonal, and genetic correlates of volunteering to any significant extent, especially controlling for other factors as potential confounds. Evolutionary theory and behavioral genetic research suggest the importance of such physiological factors in humans. Basically, many aspects of social relationships and social activities have effects on health (e.g., Newman and Roberts 2013; Uchino 2004), as the widely used biopsychosocial (BPS) model suggests (Institute of Medicine 2001). Studies of formal volunteering (FV), charitable giving, and altruistic behavior suggest that physiological characteristics are related to volunteering, including specific genes (such as oxytocin receptor [OXTR] genes, Arginine vasopressin receptor [AVPR] genes, dopamine D4 receptor [DRD4] genes, and 5-HTTLPR). We recommend that future research on physiological factors be extended to non-Western populations, focusing specifically on volunteering, and differentiating between different forms and types of volunteering and civic participation