Single photon excitations of optical fields can be used to encode quantum information, but coherent processing of that information is difficult. While single qubit gates are trivial, two qubit entangling gates are very difficult. Typically photons do not interact except in so far as mediated by matter through, for example, the Kerr mutual phase shift. Such phase shifts are currently far too small to be a practical path to entangling gates for single photons.

In this talk, I will describe an alternative approach to entangling single photons using the nonunitary change of a state of a multimode system when conditioned on a measurement outcome on a subset of those modes. Such gates are non deterministic and may fail, but success is heralded by a measurement signal. There are now a number of different schemes of this kind, including optical cluster state implementations of the one-way quantum computer. I will review the current status of the field and describe recent experimental progress.

Last updated on Monday, 20 February 2006 by Victor Yakovenko