A symmetry analyser for non-destructive Bell state detection using weak nonlinearities
Physical Review A 71, 060302, Rapid Communication (2005)
We describe a novel method to project photonic two-qubit states onto the symmetric and antisymmetric subspaces of their Hilbert space. This device utilizes a weak cross-Kerr non-linearity, generated, for example, by electromagnetically induced transparency. The symmetry analyser is non-destructive, and works for small values of the cross-Kerr coupling. Furthermore, the device can be used to construct a quantum non-demolition Bell state analyser and detector.