Optics and Photonics Society of Iran

In this paper, the dependence of the spectral entanglement of photon pairs generated by spontaneous parametric               down-conversion process on the bandwidth of the spectral filters used in the detection setup of photon pairs has been studied. SPDC process is a three-wave mixing that is carried out in a nonlinear crystal and the entangled photon pairs generated by this process are used in various fields such as quantum computing, quantum cryptography and quantum communication. The amount of entanglement of the quantum system (photon pairs) is determined by the entanglement entropy, which provides a measure for disorder in the system. At first eigenvalue equations of the reduced density operator of signal and idler photons according to the parameter of filter bandwidth of the detection setup has been obtained, Then by solving the eigenvalue equations numerically, different values of the Schmidt coefficients is calculated in terms of different values of the spectral bandwidth. Finally the dependence of the spectral entanglement of photon pairs is reported by the entanglement entropy calculations.