Rydberg-atom δ-layers in silicon

In this project low-dimensional devices are made by confining group-V donors in silicon. The devices are then investigated electrically, by low temperature magnetoresistance measurements, and optically by using techniques such as Fourier transform infra-red (FTIR) spectroscopy and angle resolved photo-emission spectroscopy (ARPES). This allows to understand characteristics of the donor electrons in the Si crystal such as interactions between dopant atoms, the spin–orbit and spin–spin coupling, the metal–insulator transition, and their dependence on dopant species. The goal is to reduce the dimensionality of the confinement to one and zero dimensions and to create ordered single-atom arrays, as well as to measure their quantum coherent and electro-optic properties.
Trapped atoms or ions are an attractive platform for quantum physics and technology. They can be localized in vacuum using electromagnetic fields, or in solids during growth or subsequent implantation, where the solids must be insulators or semiconductors to act as vacuum for the atoms. After trapping, the spin and orbital states of these atoms can be manipulated using photons to realize quantum gates. Solid-state traps have obvious advantages over atomic ones, and the challenge remains to deterministically place them.

Our aim is to realize, in collaboration with our partners, a long-standing proposal to exploit single-electron donors in silicon (column V elements) for Si-based quantum processors. The devices consist of few nm thick layers of isolated donor atoms such as phosphorus and arsenic, which can be biased and read-out electrically through metallically-doped contacts, and controlled optically with THz radiation.

We are using our unique access to the intense THz radiation of the Swiss Synchrotron Light Source (SLS) at the Paul Scherrer Institut, and to a dilution refrigerator with optical access and a vector magnet to investigate and improve these thin-layer devices. With the future ordered arrays of single donors, we will use short, coherent THz pulses to coherently control their orbital states, and use the subsequent change of their spatial extent to create gates coupling between other donor species.