Two-photon absorption and self-phase modulation in InGaAsP/InP multi-quantum-well waveguides

We report the first measurement of two-photon absorption (TPA) and self-phase modulation in an InGaAsP/InP multi-quantum-well waveguide. The TPA coefficient, β2, was found to be 60±10 cm/GW at 1.55 μm. Despite operating at 200 nm from the band edge, self-phase modulation as high as 8±2 rad was observed for 30-ps optical pulses at 3.8-W peak input power. A theoretical calculation indicates that this enhanced phase modulation is primarily due to bandfilling in the quantum wells and the free-carrier plasma effect.

Magnetotunnelling spectroscopy: an experimental tool for studying chaos in quantum transport

Resonant tunnelling spectroscopy is used to investigate the energy level spectrum of a wide potential well in the presence of a large magnetic field oriented at angles θ between 0° and 90° to the normal to the plane of the well. In the tilted field geometry, the current-voltage characteristics exhibit a large number of quasiperiodic resonant peaks even though the classical motion of electrons in the potential well is chaotic. The voltage range and spacing of the resonances both change dramatically with θ. We give a quantitative explanation for this behaviour by considering the classical period of unstable periodic orbits within the chaotic sea of the potential well.

Low power all-optical switch in a passive InGaAsP multiple quantum well waveguide

We demonstrate the use of resonant bandfilling nonlinearity in an InGaAsP/InGaAsP Multiple Quantum Well (MQW) waveguide due to photogenerated carriers to obtain switching at pulse powers, which can readily be obtained from an erbium amplified diode laser source. In order to produce gating a polarisation rotation gate was used, which relies on an asymmetry in the nonlinear refraction on the principle axes of the waveguide.

Single-photon detection using a quantum dot field effect transistor

A novel device for detection of single photons based on a GaAs/AlGaAs modulation doped field effect transistor (MODFET) which does not rely on avalanche processes is proposed. The optimal channel electron densities and quantum dot parameters for detection of single photons are discussed.

Novel designs for Penning ion traps

A number of alternative designs are presented for Penning ion traps suitable for quantum information processing (QIP) applications with atomic ions. The first trap design is a simple array of long straight wires, which allows easy optical access. A prototype of this trap has been built to trap Ca+ and a simple electronic detection scheme has been employed to demonstrate the operation of the trap. Another trap design consists of a conducting plate with a hole in it situated above a continuous conducting plane. The final trap design is based on an array of pad electrodes. Although this trap design lacks the open geometry of the other traps described above, the pad design may prove useful in a hybrid scheme in which information processing and qubit storage take place in different types of trap. The behaviour of the pad traps is simulated numerically and techniques for moving ions rapidly between traps are discussed. Future experiments with these various designs are discussed. All of the designs lend themselves to the construction of multiple trap arrays, as required for scalable ion trap QIP.

Comparison of quantum chemistry calculation methods of nucleic acid base-quartets

Nine base-quartets were calculated by six semi-empirical methods and ab initio Hartree-Fork method using STO-3G basis set. The results showed that PM3 method can be use to calculate base quartets, the results of PM3 calculations are close to the ab initio