Nature Nanotech. http://dx.doi.org/10.1038/nnano.2011.190 (2011)

The leading proposal for a solid-state quantum computer that works at room temperature relies on the electronic, spin and optical characteristics of discrete point defects in diamond. Diamond is a good host for spin-based quantum computing because it has very few nuclear spins of its own, and it is able to host defects — most notably nitrogen–vacancy centres — that barely interact with the surrounding lattice. By creating an array of these defects, it might be possible to encode an ensemble of coupled quantum bits in their spins.

One way of enhancing the coupling between qubits of such an array is to embed them in an optical cavity — most obviously by forming a cavity out of diamond itself. What's needed is a narrow-resonance, high-quality cavity that avoids losses to phonon modes and other non-radiative channels, but this has proved difficult to achieve in diamond.

Janine Riedrich-Möller and colleagues have gone some way to overcoming the difficulties by using focused ion-beam milling to create one- and two-dimensional photonic-crystal cavities in suspended single-crystal diamond membranes. They can then tune the characteristics of the cavities to enhance the zero-phonon photoluminescent emission of silicon–vacancy defects present in the diamond.