, Results Ancilla: a single photon Simplest type of ancilla, no known scheme ? Polarization-preserving bound predicts P succ ? 1

, ? Numerical search confirms the result Do entangled ancillae help? ? Grice's one-Bell-pair: optimal 3 4 , by numerical search Conclusion Achievements What can we say on the optimal P succ of unambiguous Bell measurement? ? Upper bound for polarization-preserving interferometers, saturated by known schemes ? Hybrid numerical/symbolical search ? Confirms optimality of (some) known schemes ? New 2

, Explored several ancillae?? 3 4 stays the best (for small networks)