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A Bell-state measurement distinguishes the four two-qubit Bell states. Ideally its four measurement operators are the rank-one orthogonal projectors onto $|{\Phi }^{+}⟩$, $|{\Phi }^{-}⟩$, $|{\Psi }^{+}⟩$ and $|{\Psi }^{-}⟩$. It measures joint parity and relative-phase information, rather than the two qubits separately in one local basis.

A circuit realization applies a CNOT gate with the first qubit as control, then a Hadamard gate to that qubit, followed by computational-basis measurements of both. These gates map the Bell basis to four distinct computational-basis states. A complete result therefore carries two classical bits and supplies the correction label in ideal quantum teleportation. A restricted experimental analyzer may distinguish fewer than all four outcomes.

Dik Bouwmeester coauthored the 1997 optical demonstration of quantum teleportation. A joint Bell-state measurement on an input photon and one member of an entangled pair conditionally transferred the input polarization quantum state to the other member. The reported experiment selected a particular detected outcome. The process consumes the shared entanglement and requires classical information about the measurement result; it does not send a usable message faster than light.^[ref]

A physicist researching quantum optics and quantum information science.^[ref]

Jian-Wei Pan coauthored an optical demonstration of entanglement swapping. Starting with two separate entangled photon pairs, a joint Bell-state measurement on one photon from each pair conditionally prepared the remaining two photons in an entangled state, although those two photons had not interacted. The resulting correlations are conditioned on the joint measurement record, which is essential when comparing the data.^[ref]

A physicist researching experimental quantum information science.^[ref]