Coherent control of indirect excitonic qubits in optically driven quantum dot molecules

Abstract

We propose an optoelectronic scheme to define and manipulate an indirect neutral exciton qubit within a quantum dot molecule. We demonstrate coherent dynamics of indirect excitons resilient against decoherence effects, including direct exciton spontaneous recombination. For molecules with large interdot separation, the exciton dressed spectrum yields an often overlooked avoided crossing between spatially indirect exciton states. Effective two-level system Hamiltonians are extracted by Feshbach projection over the multilevel exciton configurations. An adiabatic manipulation of the qubit states is devised using time-dependent electric field sweeps. The exciton dynamics yields the necessary conditions for qubit initialization and near unitary rotations in the picosecond time scale, driven by the system internal dynamics. Despite the strong influence of laser excitation, charge tunneling, and interdot dipole-dipole interactions, the effective relaxation time of indirect excitons is much longer than the direct exciton spontaneous recombination time, rendering indirect excitons as potential elemental qubits in more complex schemes.