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Coherent control of donor atom orbits in silicon for quantum information technologies

Shallow donor impurities in silicon, once frozen out at low temperature, share many properties in common with free hydrogen atoms, with a single spin-half electron orbiting a singly positively charged spin-half core. Although the wavefunctions are mesoscale, they have interesting differences with those of free atoms in vacuum (see figure). They have held the record for the longest electronic spin relaxation lifetimes in the solid state for over half a century, and the nuclear spin relaxation has been extended to hours by isotopic purification. Orbital excitations have long been the subject of spectroscopic investigation - but it is only in the last decade that it has been possible to control the time-domain dynamics of orbital excitations such as the 1s to 2p, due to the difficulty of obtaining short, intense pulses in the relevant wavelength range, around 10THz. The most flexible source for study is the Free Electron Laser, such as FELIX in Nijmegen. They provide new techniques that make shallow donors attractive for studying atomic physics effects, and for applications in quantum information.

In this talk I will review our work on dynamics and spectroscopy, illustrating the flexibility of THz pulsed control now achievable for controlling the electron orbit, and discuss how single atom devices might be achieved, and show how donor states in silicon provide extremely attractive possibilities for non-linear optics.