Light-matter cocktail preserves quantum states in diamond

Scientists at the University of Santa Barbara have, in the words of graduate student Bob Buckley, managed to "manipulate the quantum state of a single electron in a semiconductor without destroying the information", by very briefly forming a mixture of light and matter.

From the announcement: Using electrons trapped in a single atom-sized defect within a thin crystal of diamond, combined with laser light of precisely the right color, the scientists showed that it was possible to briefly form a mixture of light and matter. After forming this light-matter mixture, they were able to use measurements of the light to determine the state of the electrons.

The team was also able to show that the light modified, but did not destroy the configuration of the electrons; that is, the quantum state was preserved. Measuring a quantum property without destroying it is, to say the least, a neat trick. The Idiot's Guide to Quantum Mechanics would have us believe that to measure a quantum system is to destroy the information it contains.

And yet, in the abstract of the paper published in Science Express, the authors state: We demonstrate dispersive, single-spin coupling to light for both non-destructive spin measurement through the Faraday effect and coherent spin manipulation through the optical Stark effect. These interactions can enable the coherent exchange of quantum information between single nitrogen-vacancy spins and light, facilitating coherent measurement, control, and entanglement that is scalable over large distances.

Buckley suggests that diamond could one day become as important to quantum computing as silicon is to the world of conventional computing.