Quantum molecule in the low-electron limit

Coupled few-electron dots with incorporated quantum point-contact charge detectors have been successfully fabricated and studied both experimentally and theoretically. In this paper we focus on charge detection measurements for the regimes most relevant to spin and charge qubit applications. We first characterize the degree of coherence of a single electron trapped in the double dot by measuring the average occupation of one of the dots at equilibrium. We find that the spin degree of freedom dramatically affects the charge states when a second electron is added to the system, resulting in novel charge transfer patterns. The patterns evolve as a function of tunnel coupling and magnetic field. A nonequilibrium occupation of ground and excited states as a possible origin of the observed phenomena is investigated theoretically through extensive numerical and CI calculations of 1–3 electron states for realistic confining potentials.