Future communication and computation technologies that exploit quantum information require robust and well-isolated qubits. Electron spins in III-V semiconductor quantum dots, while promising candidates, see their dynamics limited by undesirable hysteresis and decohering effects of the nuclear spin bath. Replacing electrons with holes should suppress the hyperfine interaction and consequently eliminate strong nuclear effects. Using picosecond optical pulses, we demonstrate coherent control of a single hole qubit and examine both free-induction and spin-echo decay. In moving from electrons to holes, we observe significantly reduced hyperfine interactions, evidenced by the reemergence of hysteresis-free dynamics, while obtaining similar coherence times, limited by non-nuclear mechanisms. These results demonstrate the potential of optically controlled, quantum dot hole qubits. arXiv:1106.5676v1 [quant-ph]

Al0.6Ga0.4As/GaAs/Al0.6Ga0.4As double-barrier resonant-tunneling diodes (RTD) were grown by molecular beam epitaxy with a nearby, lattice-matched Ga0.89In0.11N0.04As0.96 absorption layer. RTD mesas with ring contacts and an aperture for optical excitation of charge carriers were fabricated on the epitaxial layers. Electrical and optical properties of the RTDs were investigated for different thicknesses of a thin GaAs spacer layer incorporated between the AlGaAs tunnel barrier adjacent to the GaInNAs absorption layer. Illumination of the RTDs with laser light of 1.3 μm wavelength leads to a pronounced photo-effect with a sensitivities of around 103 A/W.

No abstract

Laser structures designed for the emission at 1.3μm and based on an active region containing InAsN quantum dots (QDs) embedded in GaInNAs∕GaAs quantum wells (QWs) have been investigated by contactless electroreflectance. Optical transitions related to both the dots and the wells have been observed and the energies of the latter have been calculated using the effective mass approach. It has been shown that QW confines one electron, one light-hole, and three heavy-hole states only and the energy separation between the QD and QW ground state transitions is approximately 250meV, which is ten times higher than the thermal energy at room temperature.

No abstract