Physik nanostrukturierter Systeme

14.01.2008 : Andrew Ferguson, Cavendish Laboratory, Cambridge

Quantum dots and radio-frequency electrometers in silicon

An important goal for solid-state quantum computing is to confine a single electron in silicon, then manipulate and subsequently determine its spin state. Silicon has a low nuclear spin density which, together with the low spin-orbit coupling in this material, is expected yield very long spin relaxation times.

I will present recent results on silicon quantum dots with tuneable tunnel barriers. Low-temperature electrical transport measurements are performed in both the many electron (N~100) and the few electron (N~10) regimes. In the few electron regime, excited states in the bias spectroscopy provide evidence for quantum confinement.

In the second part of this talk, I will discuss the same device geometry but now configured as a radio-frequency electrometer. With the quantum dot embedded in a resonant tank circuit charge, charge sensitivities of dq<10-5 eHz-0.5 are demonstrated with MHz bandwidth. This performance is comparable to aluminium radio-frequency single electron transistors.

Future aims are to perform charge sensing measurements on the quantum dot with the radio-frequency electrometer, and to engineer the quantum dot towards the single electron level.