Measurement of electronic Fabry-Perot interferometers optimized for high edge state velocity

Electronic Fabry-Perot interferometers may be used to probe the properties of electrons and quasiparticles in the quantum Hall regime. The visibility of interference is limited by finite coherence time and edge state velocity. We present two methods for enhancing the edge state velocity in GaAs/AlGaAs heterostructures by increasing the sharpness of the confining potential at the edge. The first method involves a gating scheme utilizing a combination of negatively biased gates to define the interference path and positively biased helper gates; the abrupt interface between positive and negative gate bias yields a sharp edge potential in the 2DEG. The second method involves novel heterostructures with parallel conducting quantum wells positioned with a short setback from the primary quantum well; when negative bias is applied to surface gates, the proximity of the additional quantum wells results in sharp confining potential in the primary quantum well. The devices are measured in a dilution refrigerator at T~10mK in high magnetic field. Efforts are underway to utilize these interferometers in the fractional quantum Hall regime, where interference may be used to probe exotic quasiparticle statistics.