Coherent Control and Spectroscopy of a Semiconductor Quantum Dot Wigner Molecule.

Semiconductor quantum dots containing more than one electron have found wide application in qubits, where they enable readout and enhance polarizability. However, coherent control in such dots has typically been restricted to only the lowest two levels, and such control in the strongly interacting regime has not been realized. Here we report quantum control of eight different transitions in a silicon-based quantum dot. We use qubit readout to perform spectroscopy, revealing a dense set of energy levels with characteristic spacing far smaller than the single-particle energy. By comparing with full configuration interaction calculations, we argue that the dense set of levels arises from Wigner-molecule physics.

Characterization of a gate-defined double quantum dot in a Si/SiGe nanomembrane.

We report the fabrication and characterization of a gate-defined double quantum dot formed in a Si/SiGe nanomembrane. In the past, all gate-defined quantum dots in Si/SiGe heterostructures were formed on top of strain-graded virtual substrates. The strain grading process necessarily introduces misfit dislocations into a heterostructure, and these defects introduce lateral strain inhomogeneities, mosaic tilt, and threading dislocations. The use of a SiGe nanomembrane as the virtual substrate enables the strain relaxation to be entirely elastic, eliminating the need for misfit dislocations. However, in this approach the formation of the heterostructure is more complicated, involving two separate epitaxial growth procedures separated by a wet-transfer process that results in a buried non-epitaxial interface 625 nm from the quantum dot. We demonstrate that in spite of this buried interface in close proximity to the device, a double quantum dot can be formed that is controllable enough to enable tuning of the inter-dot tunnel coupling, the identification of spin states, and the measurement of a singlet-to-triplet transition as a function of an applied magnetic field.

Driving-induced stress in urban college students.

Urban college student commuters (N = 407) were surveyed about their experiences with stress induced by driving. Of the participants 23.6% reported becoming angry at another driver more than once per day. They rated stress from other drivers as equal to the stress experienced during a college examination but gave slightly lower ratings to traffic congestion, road construction, and finding a parking place as sources of stress. Slow drivers, a child not restrained, and a vehicle following too closely were the highest rated annoying situations. Of participants, 21.6% had reported another driver to the police; nearly 22% said they carried a weapon for protection from other drivers (5.4% said a gun). Men were more than twice as likely as women to carry a weapon and three times as likely to carry a gun. Of the total sample, 19.1% feared being shot by another driver. Most participants (75.8%) said drivers were more aggressive and dangerous than they were five years ago.

Verbal behavior: The other reviews.

The extensive attention devoted to Noam Chomsky's review of Verbal Behavior by B.F. Skinner has resulted in a neglect of more than a dozen other rewiews of the work. These are surveyed and found to be positive and congenial in tone, with many of the reviewers advancing his/her own analysis of speech and language. The dominant criticism of the book was its disregard of central or implicit processes and its lack of experimental data. An examination of the receptive history of Verbal Behavior offers a more balanced historical account than those which rely excessively on Chomsky's commentary.

Verbal behavior and the history of linguistics.

A recent paper by a historian of linguistics suggests that after many years of neglect linquists are finding value in the analysis of verbal behavior developed by B.F. Skinner.

Teaching an autistic child pedestrian skills.

An autistic child was taught pedestrian skills in a classroom by use of a model of the streets and the intersection she most often frequented. She manipulated a doll and verbalized what the doll was doing to get to the designated location. After mastering the pedestrian skills on the model, video recordings familiarized her with traffic at local intersections. She successfully generalized the pedestrian skills to the natural environment.