| This thesis examines phase coherent ballistic electron transport in the two-dimensional electron gas formed in a remotely doped GaAs/Al{dollar}sb{lcub}rm x{rcub}{dollar}Ga{dollar}sb{lcub}rm 1-x{rcub}{dollar}As heterostructure. As a precursor to these measurements, the weak localization effect in an array of narrow channels is used to measure the electronic phase coherence time at temperatures between 4.2 K and 100 mK. The measured values agree well with those predicted by theories based on electron-electron interactions above 200 mK; below this temperature there is an apparent saturation in the amplitude of the localization correction.; Next we report on the observation of coherent backscattering in very open ballistic devices consisting of a quantum point contact and two reflector gates. Unlike quantum billiards in which this effect has previously been measured, our devices are designed to yield many backscattered trajectories enclosing very similar areas. An array of devices is used to average away magnetoconductance fluctuations, which would otherwise prevent a quantitative analysis of the coherent backscattering effect in our system.; We also report on measurements in which quantum interference of forward-scattered trajectories is studied. These devices consist of two closely-spaced point contacts and a reflector gate. Electrons may travel between the point contacts directly or by scattering off the reflector. Quantum interference between these two paths is evident when a perpendicular magnetic field is applied. In addition, interference oscillations are also observed by changing the bias voltage applied to the reflector gate, allowing our devices to function as electron interferometers.; Strong, periodic conductance oscillations are observed at low temperatures in electron interferometers very similar to a Fabry-Perot cavity. The devices consist of a quantum point contact in the tunneling regime and a single reflector gate designed to focus reflected electrons back to the point contact. By changing the spacing between the reflector and point contact, we observe the conductance resonances due to constructive and destructive interference of multiply-scattered electron waves within the cavity. |
