Entangler and analyzer for four-photon

An entangler is proposed for generating χ-type polarization-entangled state using an EPR entangler, two Controlled-NOT (CNOT) gates and a Controlled-Z (CZ) gate. Furthermore, we also describe how to construct an analyzer for the sixteen χ-type entangled states with some m-qubit (m ≥ 2) parity gates and CNOT gates. Since the m-qubit parity gate can be constructed by m two-qubit CZ or CNOT gates, and the two-qubit parity gate can be configured to act as a Bell-state entangler, the implementation of the photonic two-qubit parity, CNOT and CZ gates is the key points in our scheme