Non-invasive detection of the ionic and covalent charge states of an isolated double dot system

Coupled quantum dots are potential candidates to serve as qubits in quantum computation. We use a non-invasive voltage probe to study a double quantum dot system when it is coupled to the electron reservoirs and when it is isolated from them—a regime not accessible by conventional conductance measurements. Our results suggest that the dephasing time may be enhanced by isolating the dots from the electron reservoirs. We also observe features that may represent electrons tunnelling between the dots via symmetric and anti-symmetric states of the double dot molecule.