Remote interactions on two distributed quantum systems： nonlocal unambiguous quantum-state discrimination

Remote quantum-state discrimination is a critical step for the implementation of quantum communication network and distributed quantum computation. We present a protocol for remotely implementing the unambiguous discrimination between nonorthogonal states using quantum entanglements, local operations, and classical communications. This protocol consists of a remote generalized measurement described by a positive operator valued measurement （POVM）. We explicitly construct the required remote POVM. The remote POVM can be realized by performing a nonlocal controlled-rotation operation on two spatially separated qubits, one is an ancillary qubit and the other is the qubit which is encoded by two nonorthogonal states to be distinguished, and a conventional local Von Neumann orthogonal measurement on the ancilla. The particular pair of states that can be remotely and unambiguously distinguished is specified by the state of the ancilla. The probability of successful discrimination is not optimal for all admissible pairs. However, for some subset it can be very close to an optimal value in an ordinary local POVM.

Remote interactions on two distributed quantum systems: nonlocal unambiguous quantum-state discrimination

Remote quantum-state discrimination is a critical step for theimplementation of quantum communication network and distributedquantum computation. We present a protocol for remotely implementingthe unambiguous discrimination between nonorthogonal states usingquantum entanglements, local operations, and classicalcommunications. This protocol consists of a remote generalizedmeasurement described by a positive operator valued measurement(POVM). We explicitly construct the required remote POVM. The remotePOVM can be realized by performing a nonlocal controlled-rotationoperation on two spatially separated qubits, one is an ancillaryqubit and the other is the qubit which is encoded by twononorthogonal states to be distinguished, and a conventional localVon Neumann orthogonal measurement on the ancilla. The particularpair of states that can be remotely and unambiguously distinguishedis specified by the state of the ancilla. The probability ofsuccessful discrimination is not optimal for all admissible pairs.However, for some subset it can be very close to an optimal value inan ordinary local POVM.