Detecting Optical Correlations via Local Photon Subtraction

Detecting and characterizing correlations are common subjects in quantum information theory, which have recently become increasingly essential in various quantum information tasks. A quantifier of correlations is introduced for two-mode Bosonic states defined as the difference between global and local coherence caused by local photon subtraction. The fundamental properties and physical significance of this quantifier are revealed. Additionally, the amount of correlations is analyzed in the output states resulting from input product states through bilinear interactions. The quantifier of correlations is illustrated using typical two-mode Bosonic states and its effectiveness is compared with other existing measures of correlations, such as entanglement and quantum discord.