Quantum nonlocality without entanglement in a pair of qubits

Understand

We consider unambiguous discrimination of two separable bipartite states, one being pure and the other being a rank-2 mixed state.

• There is a gap between the optimal success probability under global measurements and the one achieved by generalized measurements with separable measurement operators.
• We show that even the latter success probability cannot be achieved via local operations and classical communication, leaving a nonzero gap in between.