Tunable spin loading and T1 of a silicon spin qubit measured by single-shot readout.

We demonstrate single-shot readout of a silicon quantum dot spin qubit, and we measure the spin relaxation time T1. We show that the rate of spin loading can be tuned by an order of magnitude by changing the amplitude of a pulsed-gate voltage, and the fraction of spin-up electrons loaded can also be controlled. This tunability arises because electron spins can be loaded through an orbital excited state. Using a theory that includes excited states of the dot and energy-dependent tunneling, we find that a global fit to the loading rate and spin-up fraction is in good agreement with the data.

Charge sensing and controllable tunnel coupling in a Si/SiGe double quantum dot.

We report integrated charge sensing measurements on a Si/SiGe double quantum dot. The quantum dot is shown to be tunable from a single, large dot to a well-isolated double dot. Charge sensing measurements enable the extraction of the tunnel coupling t between the quantum dots as a function of the voltage on the top gates defining the device. Control of the voltage on a single such gate tunes the barrier separating the two dots. The measured tunnel coupling is an exponential function of the gate voltage. The ability to control t is an important step toward controlling spin qubits in silicon quantum dots.

Theory of the transition at 0.2 K in Ni-doped Bi2Sr2CaCu2O8

A theory is put forward that the electronic phase transition at 0.2 K in Ni-doped Bi2Sr2CaCu2O8 is a result of the formation of a spin density wave in the system of Ni impurities. The driving force for the transition is the exchange interaction between the impurity spins and the spins of the conduction electrons. This creates a small gap at two of the four nodes of the superconducting gap. The effect is to reduce the thermal conductivity by a factor of 2, as observed.

Pseudogaps and extrinsic losses in photoemission experiments on poorly conducting solids

A photoelectron emitted from a conducting solid may suffer a substantial energy change through ohmic losses that can drastically alter the line shape on the millielectron volt scale that is now observable through improved resolution. Almost all of this energy loss occurs after the electron leaves the solid. These losses are expected to be important in isotropic materials with relatively low conductivity, such as certain colossal magnetoresistance manganates, and in very electrically anisotropic materials, such as one-dimensional conductors, and may also affect interpretation of photoemission in superconductors with high transition temperatures. The electric field of the photoelectron can penetrate the solid, and extrinsic losses of this type can mimic pseudogap effects and other peculiar features of photoemission in cubic manganates, as illustrated for La0.67Ca0.33MnO3.

Effect of restorative materials on cuspal flexure.

The purposes of this study were (1) to establish a methodology for determining surface strains in two locations of the same tooth under intact, prepared, and restored conditions and (2) to compare the effects on stiffness of different restorative materials in a tooth subjected to cuspal loading. Two linear strain gauges were mounted on each of 30 extracted maxillary premolar teeth. Teeth were mounted in poly(methyl methacrylate) resin and randomly assigned to one of three study groups according to the restorative material and application technique to be used. Statistical analysis indicated a statistically significant interaction between restorative material and tooth condition at both proximal and buccal sites and a statistically significant difference in stiffness between teeth restored with Tenure/Marathon V and those restored with either amalgam or Scotchbond 2/P-50 at the proximal site. Results suggest that the methods employed provide a useful, nondestructive means of testing the same tooth under various conditions.

Neurology.

Carotid endarterectomy is beneficial for patients with asymptomatic carotid stenosis exceeding 60% of diameter reduction. The Framingham Heart Study group identified left ventricular mass as an additional risk factor for strokes. Betaseron has been approved for the treatment of selected patients with multiple sclerosis.

Neurology.

The unstable trinucleotide repeat continues to turn up as the genetic defect in several inherited neurologic disorders. With dementia, certain clinical events are more common in vascular disease than in Alzheimer's disease. An ongoing controversy, and often a legal issue, is the role of trauma in either causing or exacerbating multiple sclerosis.