Generation and spectral engineering of pulsed polarization entangled states

The quantum state of the photon pair generated from type-II spontaneous parametric down-conversion pumped by a ultrafast laser pulse exhibits strong decoherence in its polarization entanglement, an effect which can be attributed to the clock effect of the pump pulse or, equivalently, to distinguishing spectral information in the two-photon state. Here, we discuss novel spectral engineering techniques to eliminate these detrimental decoherence effects. In addition, spectral engineering provides a means for generating polarization entangled states with novel spectral characteristics: the frequency-correlated state and the frequency-uncorrelated state. Such states may find usefulness in experimental quantum information science and quantum metrology applications.