Quantum interference in two independently tunable parallel quantum point contacts

We have fabricated two independently tunable quantum point contacts in a parallel configuration, by wet etching a 2,000 Å diameter hole in the center of the constriction of a split-gate quantum point contact in an AlGaAs/GaAs heterojunction. The number of occupied subbands in each of the two channels on either side of the etched hole can be tuned independently by biasing the gates, with each channel exhibiting quantized conductance steps at integer multiples of 2e²/h, independent of the other. For B in the quantum Hall regime, periodic resistance oscillations are observed when both gate biases are fixed and B is swept. Further, periodic resistance oscillations are also observed when B and the bias on one gate is fixed, while the bias on the second gate is swept. In both cases the fluctuations are due to tunneling between opposite edge channels via magnetically bound 'edge' states encircling the etched hole, whose energies are quantized such that each encloses an integral number of flux quanta.