Spin readout and initialization in a semiconductor quantum dot

Electron spin qubits in semiconductors are attractive from the viewpoint of long coherence times. However, single spin measurement is challenging. Several promising schemes incorporate ancillary tunnel couplings that may provide unwanted channels for decoherence. Here, we propose a novel spin-charge transduction scheme, converting spin information to orbital information within a single quantum dot by microwave excitation. The same quantum dot can be used for rapid initialization, gating, and readout. We present detailed modeling of such a device in silicon to confirm its feasibility.     

Theoretical study of the critical current of YBa2Cu3O7−δ bicrystals with hole-deficient grain boundaries

We develop a theory of the critical current across grain boundaries in YBa₂Cu₃O_7−δ bicrystals. Experiments have shown that there is hole depletion near a boundary and the concentration profiles have been determined for specific cases. These results mean that the critical temperature is a function of distance from the boundary. Taking this function from experiment as input into the theory, we study two specific boundaries: a boundary with a 7° misorientation angle about [100] which is known to be strongly coupled for the purposes of current flow, and a 31° boundary which is known to be weakly coupled. Using Ginzburg-Landau theory, we determine the dependence of the critical current density (j_c) on temperature and the spatial dependence of the order parameter for these boundaries. The results show that the oxygen depletion can account for a major portion of the change from weak to strong coupling of boundaries as the misorientation angle is increased.     

Stochastic frequency-domain tissue characterization: application to human spleens ‘in vivo’

Ultrasonic waveforms backscattered from normal and pathologic human spleens were recorded in vivo using a high-speed digital data acquisition system. A frequency-domain analysis was performed for 50 digitized waveforms from each spleen, in which auto-correlations of frequency spectra were employed to measure the mean spacing among adjacent tissue scatterers. Mean scatterer spacing for normal spleens averaged 1.10 ± 0.14 mm, whereas abnormal, diffusely enlarged spleens had mean scatterer spacings averaging 1.52 ± 0.14 mm. The results of these measurements are in accord with those expected from splenic histology. The techniques described may be valuable in ultrasonic diagnosis of the spleen and other organs.