Embedded Bell-state analysis
Paul G. Kwiat, Harald Weinfurter · Physical Review A · 1998
We discuss a method for distinguishing the four orthogonal Bell states of two entangled particles. Because the scheme relies only on linear optical elements, it should be realizable with current technology. The new feature is that the Bell states must be embedded in a larger Hilbert space. That is, the correlated particles must be entangled in more than one degree of freedom.