Optimal control of universal quantum gates in a double quantum dot

Abstract

We theoretically investigate electron spin operations driven by applied electric fields in a semiconductor double quantum dot (DQD). Our model describes a DQD formed in semiconductor nanowire with longitudinal potential modulated by local gating. The eigenstates for two electron occupation, including spin-orbit interaction, are calculated and then used to construct a model for the charge transport cycle in the DQD taking into account the spatial dependence and spin mixing of states. The dynamics of the system is simulated aiming at implementing protocols for qubit operations, that is, controlled transitions between the singlet and triplet states. In order to obtain fast spin manipulation, the dynamics is carried out taking advantage of the anticrossings of energy levels introduced by the spin-orbit and interdot couplings. The theory of optimal quantum control is invoked to find the specific electric-field driving that performs qubit logical operations. We demonstrate that it is possible to perform within high efficiency a universal set of quantum gates $\{$CNOT, H$\otimes$I, I$\otimes$H, T$\otimes$I, and T$\otimes$I$\}$, where H is the Hadamard gate, T is the $\pi/8$ gate, and I is the identity, even in the presence of a fast charge transport cycle and charge noise effects.