On measuring dangling bond charge qubit dynamics

A closely-spaced silicon-surface dangling bond (DB) pair, sharing one excess electron, is an excellent candidate for a charge qubit. DBs are atomic scale quantum dots created by selectively removing hydrogen atoms from a hydrogen-terminated silicon surface. A coupled DB pair should be highly coherent due to its atomic size; hence it has the potential to overcome the most serious obstacle of larger-scale quantum dot charge qubits, which is decoherence. However, this analysis is speculative, as the dynamics has not yet been measured experimentally. In fact, the estimated coherent dynamics of this DB charge qubit is much faster than any feasible characterization or control timescale. Inspired by earlier work, we devise a method to probe fast dynamics using much slower instruments. In our method, a dangling-bond pair is driven by a near infrared field and subject to a ramped electrical bias. The DB pair is capacitively coupled to an atomic force microscope (AFM) tip, and its dynamics are extracted from the resonances appearing on the AFM output.