Sub Decoherence Time Generation and Detection of Orbital Entanglement

Recent experiments have demonstrated sub decoherence time control of individual single-electron orbital qubits. Here we propose a quantum dot based scheme for generation and detection of pairs of orbitally entangled electrons on a timescale much shorter than the decoherence time. The electrons are entangled, via two-particle interference, and transferred to the detectors during a single cotunneling event, making the scheme insensitive to charge noise. For sufficiently long detector dot lifetimes, cross-correlation detection of the dot charges can be performed with real-time counting techniques, opening up for an unambiguous short-time Bell inequality test of orbital entanglement.Comment: 5 pages, 2 figures, 3 pages supplemental materia

Optimal geometry of lateral GaAs and Si/SiGe quantum dots for electrical control of spin qubits

We investigate the effects of the orientation of the magnetic field and the orientation of a quantum dot, with respect to crystallographic coordinates, on the quality of an electrically controlled qubit realized in a gated semiconductor quantum dot. We find that, due to the anisotropy of the spin-orbit interactions, by varying the two orientations it is possible to tune the qubit in the sense of optimizing the ratio of its couplings to phonons and to a control electric field. We find conditions under which such optimal setup can be reached by solely reorienting the magnetic field, and when a specific positioning of the dot is required. We also find that the knowledge of the relative sign of the spin-orbit interaction strengths allows to choose a robust optimal dot geometry, with the dot main axis along [110], or [110], where the qubit can be always optimized by reorienting the magnetic field

Colour categories are reflected in sensory stages of colour perception when stimulus issues are resolved

Debate exists about the time course of the effect of colour categories on visual processing. We investigated the effect of colour categories for two groups who differed in whether they categorised a blue-green boundary colour as the same- or different-category to a reliably-named blue colour and a reliably-named green colour. Colour differences were equated in just-noticeable differences to be equally discriminable. We analysed event-related potentials for these colours elicited on a passive visual oddball task and investigated the time course of categorical effects on colour processing. Support for category effects was found 100 ms after stimulus onset, and over frontal sites around 250 ms, suggesting that colour naming affects both early sensory and later stages of chromatic processing