Light is one of the most promising carriers of quantum information. It is robust against decoherence because it does not interact with stray electric and magnetic fields and passes unscathed through transparent matter.

But this prized robustness is also a serious limitation. Photons do not easily interact with each other so processing the information they carry is tricky.

In recent years, however, physicists have worked out how to make photons interact using interferometers and to carry out quantum computations using the output of one interferometer as the input for another.

The trouble is that interferometers are notoriously fickle. Sneeze and they need re-calibrating. So cascades of them tend to be hard to handle.

Today, Jonathan McDonald at the Air Force Research Laboratory in Rome New York, and a few pals reveal a way round this problem.

Their idea is to make holograms of interferometers so that their properties become 'frozen' in glass. This makes them much more stable.