Coherent control of Rydberg states in silicon

Atom manipulation in silicon When an atom is excited into a 'Rydberg' state, its electronic wavefunction can extend from less than 0.1 nanometres to several nanometres or more. This process can be used to induce and coherently control interactions between atoms that are sufficiently far apart as to be non-interacting in their normal states. Thornton Greenland and colleagues have exploited this phenomenon to achieve quantum manipulation comparable to that previously performed using laser-cooled trapped atoms, but in the solid state, on phosphorus impurity (dopant) atoms in silicon. The technique could be adapted to control small numbers of independently addressable impurity atoms at known locations, as required for the implementation of quantum logic gates. When an atom is excited into a Rydberg state, its electronic wavefunction can extend to several nanometres. This process can be used to induce and coherently control interactions between atoms that are far enough apart to be non-interacting in their normal states. Now, such behaviour has been realized in a solid-state context, by demonstrating coherent control of the wavefunctions of phosphorus dopant atoms in silicon. Laser cooling and electromagnetic traps have led to a revolution in atomic physics, yielding dramatic discoveries ranging from Bose–Einstein condensation to the quantum control of single atoms 1 . Of particular interest, because they can be used in the quantum control of one atom by another, are excited Rydberg states 2 , 3 , 4 , where wavefunctions are expanded from their ground-state extents of less than 0.1 nm to several nanometres and even beyond; this allows atoms far enough apart to be non-interacting in their ground states to strongly interact in their excited states. For eventual application of such states 5 , a solid-state implementation is very desirable. Here we demonstrate the coherent control of impurity wavefunctions in the most ubiquitous donor in a semiconductor, namely phosphorus-doped silicon. In our experiments, we use a free-electron laser to stimulate and observe photon echoes 6 , 7 , the orbital analogue of the Hahn spin echo 8 , and Rabi oscillations familiar from magnetic resonance spectroscopy. As well as extending atomic physicists’ explorations 1 , 2 , 3 , 9 of quantum phenomena to the solid state, our work adds coherent terahertz radiation, as a particularly precise regulator of orbitals in solids, to the list of controls, such as pressure and chemical compositi