MAXIMAL ENTANGLEMENT GENERATION VIA PULSED PARAMETRIC DOWNCONVERSION

A method to entangle photons in frequency is discussed. It uses narrow pump pulses and long crystals and allows the generation of maximally-entangled two-photon states that are correlated in frequency and anti-correlated in time of arrival. An experimental setup to test the entanglement of the created states is proposed. Spontaneous parametric downconversion (SPDC) is the conventional source of entanglement used in most experiments. However, the state gen-erated through SPDC using the customary phase-matching condition is max-imally entangled only when a continuous-wave (cw) pump is used1,2. In par-ticular one sees that by decreasing the pulse length, the visibility of the inter-ference experiments decreases3. Advantages in pulsed SPDC have prompted interests in finding ways to retain or to restore the entanglement even in the pulsed regime4. In this paper a method to achieve maximum entanglement in the pulsed regime is analyzed5,6. It does not require any filtering or post-selection, and it utilizes long crystals resulting in high downconversion efficiencies. While the customary phase matching condition used in SPDC crystals is appropriate for cw pumping, the phase matching conditions we propose here are devised for pulsed pumps. The biphoton twin beam state generated by conventional phase matching and cw pumping is given by |TB 〉 = d