Characterization of frequency entanglement under extended phase-matching conditions

Abstract

Frequency-entangled photon pairs generated by spontaneous parametric down-conversion process under extended phase-matching conditions are found to be prospective resources for quantum information technology. The spectral indistinguishability and the degree of frequency entanglement of the down-converted photon pairs are two key features determining their potential applications. In this paper, both figures of merits are investigated. It is shown that the broadening of the pulsed pump bandwidth, the chirping of the pulse duration, and the lengthening of the nonlinear crystal all degrade the spectral indistinguishability. Furthermore, by changing the above conditions, it is possible to transfer the entanglement type from frequency-correlated to frequency-anticorrelated. For frequency-correlated entanglement, the degree of entanglement grows linearly with the pump bandwidth and the nonlinear crystal length, and quadratically with the chirp parameter of the pulse, while for anticorrelated frequency entanglement, the degree of frequency entanglement turns to behave with an inverse dependence on the above parameters. Guided by such investigations, the generation of desired frequency-entangled source for various quantum information applications can be optimized.