Electron Spins in Single Electron Transistors

摘要

Measurements of a single electron spin showed that the excited spin state in a GaAs single electron transistor can live for as long as 1s. However, the decoherence time in the excited state is known to be short, because of the coupling to nuclear spins. Therefore, single-electron transistors in Si quantum wells have been fabricated; it is possible in principle to make the decoherence time very long by using isotopically pure Si. Nonuniform electron density in the quantum wells has made the fabrication difficult, but a path to overcoming this has been identified. Quasi-particles with fractional charge and statistics, as well as modified Coulomb interactions, exist in a two-dimensional electron system in the fractional quantum Hall (FQH) regime. Theoretical models of the FQH state at filling fraction upsilon=5/2 make the prediction that the wave function can encode the interchange of two quasi-particles, making this state relevant for topological quantum computing. Measurements of bias-dependent tunneling across a narrow constriction at upsilon=5/2 exhibit temperature scaling and, from fits to the theoretical scaling form, we extracted values for the effective charge and the interaction parameter of the quasiparticles. Ranges of values obtained are consistent with those predicted by certain models of the 5/2 state.