Optical control of coherent interactions between electron spins in InGaAs quantum dots

Coherent interactions between spins in quantum dots are a key requirement for quantum gates. We have performed pump-probe experiments in which pulsed lasers emitting at different photon energies manipulate two distinct subsets of electron spins within an inhomogeneous InGaAs quantum dot ensemble. The spin dynamics are monitored through their precession about an external magnetic field. These measurements demonstrate spin precession phase shifts and modulations of the magnitude of one subset of oriented spins after optical orientation of the second subset. The observations are consistent with results from a model using a Heisenberg-like interaction with μeV strength.     

Kinetics of dark excitons and excitonic trions in InGaAs single quantum well

Magnetooptical studies performed on a wide InGaAs/GaAs single quantum well indicate that optically non-active (dark) excitons with total angular momentum play the role of a reservoir for the creation of free multiparticle excitonic complexes. After analyzing the magnetic field evolution of the circularly polarized components of the low energy structure appearing in the main excitonic luminescence line we assign this feature to the excitonic trion formation. The binding energy of the excitonic trions was estimated to be of the order of 1 meV. Received: 29 October 1997 / Received in final form: 20 February 1998 / Accepted: 21 February 1998     

Electric field control of exciton states in quantum dot molecules

Semiconductor nanostructures have attracted considerable interest during the recent years in view of the potential application in quantum information processing. In particular, quantum dots have been suggested to fulfill an essential requirement for quantum computation: controllable interaction that couples two quantum dot qubits. Previous experiments on two vertically aligned quantum dots have demonstrated the formation of coupled exciton states. We show that this coupling between two In_0.60Ga_0.40As/GaAs quantum dots can be tuned by an electric field applied along the molecule axis. This controllable coupling in such a relatively simple configuration could be implemented in a solid-state-based quantum device.     

Structure transfer from a polymeric melt to the solid state. Part I: The influence of chain entanglements in linear polyethylene

Melt-spinning experiments were carried out at high quenching rates. Mechanical properties (elongation at break, natural draw ratio, and elastic recovery) have been measured. Significant variations of these quantities were observed when extrusion conditions were changed. This has been attributed to different states of the entanglements within the melt, which are directly transferred into the solid state. This intercorrelation between melt and solid-state properties has been substantiated in the case of rapidly cooled samples, where a poor crystallization on one side and a simultaneous good conservation of melt history on the other side are provoked.     

Time-resolved emission spectroscopy of gadolinium vanadate ceramics (GdVO4:Bi3+)

The preparation of GdVO₄:Bi³⁺ ceramics is indicated. Bismuth shows a strong tendency to evaporate during the sintering process. Time-resolved emission spectroscopy shows for sufficiently low Bi³⁺ concentrations subsequently: blue VO ₄ ^3– emission with a decay time corresponding to the transfer rate (10⁶ s^–1), yellow VO ₄ ^3– –Bi³⁺ emission, rare-earth impurity emission and VO ₄ ^3– –Bi³⁺ afterglow.