简介:Theentanglementcapacityofgeneraltwo-qubitunitaryoperatorsisstudiedwhenauxiliarysystemsareallowed,andtheanalyticalresultsbasedonlinearentropywheninputstatesaredisentangledaregiven.Fromtheresultstheconditionforperfectentangler,α_1=α_2=π/4,isobtained.Contrarytothecasewithoutauxiliarysystem,theparameterα_3mayplayactiveroletotheentanglementcapacitywhenauxiliarysystemsareallowed.