Gate control of the spin-splitting energy in a quantum dot: Application in single qubit rotation

摘要

We numerically calculate modulation of the spin-splitting energy in an asymmetric quantum dot due to an external electrostatic potential (applied via gates) that induces the Rashba spin-orbit interaction. The quantum dot has finite potential barriers and contains a built-in electric field (due to doping or compositional variation) that makes the potential profile asymmetric in space. It is placed in a magnetic field which lifts the spin degeneracy of every subband due to the Zeeman effect and we calculate by how much the Rashba interaction can change the total spin-splitting energy in the lowest subband. In the past, a perturbative solution that ignored "spin texturing" effects indicated that (1) the Rashba interaction always increases the total spin-splitting energy and that (2) the increase is a negligible fraction (<0.1%) of the total spin-splitting energy for reasonable parameters. The more accurate non-perturbative solution presented here accounts for spin texturing and shows that (1) the total spin-splitting energy may actually decrease (instead of increasing) owing to the Rashba effect and that (2) the Rashba interaction can decrease the spin-splitting energy by >50% for reasonable parameters. A modulation this large can be used for single qubit rotation in a quantum gate.