US Patent 7359101 Tests of quantum information

Quantum testing can compare unknown photon states in a manner suitable for a validation check of a quantum digital signature, testing of the operation of a quantum gate, or detecting of entanglement. The effect of the QSC system can be used to entangle input photon states. QSC system can include a control swap gate having a control channel that is measured, a beam splitter and a controlled phases gate with a control channel that is measured, or a beam splitter with a parity detector on an output channel. The operation of the QSC system can also be used to generate an entangled photon state.