Entanglement and interference between different degrees of freedom of photon states
Fang‐Wen Sun, Bi‐Heng Liu, Yun‐Feng Huang, Y. S. Zhang, Z. Y. Ou, Guang‐Can Guo · Physical Review A · 2007
In this paper, photonic entanglement and interference are described and analyzed with the language of quantum information processing. Correspondingly, a photon state involving several degrees of freedom is represented in an expression based on the permutation symmetry of bosons. In this expression, each degree of freedom of a single photon is regarded as a qubit and operations on photons as qubit gates. The two-photon Hong-Ou-Mandel interference is well interpreted with it. Moreover, the analysis reveals the entanglement between different degrees of freedom in a four-photon state from parametric down conversion, even if there is no entanglement between them in the two-photon state. The entanglement will decrease the state purity and photon interference visibility in the experiments on a four-photon polarization state.