Efficient generation of polarization-entangled photons in a nonlinear crystal
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We review the use of bidirectional pumping and collinear propagation in type-II phase-matched periodically poled KTiOPO4 to achieve efficient generation of polarization-entangled photons via spontaneous parametric downconversion. The advantages of this approach are fully exploited in our optimized polarization Sagnac interferometric source. Its measured flux of 4700 polarization-entangled photon pairs/s per milliwatt of pump power in a 1-nm bandwidth exhibited 99% quantum-interference visibility. We also present a plane-wave Gaussian state theory for continuous-wave spontaneous parametric downconversion. This formulation affords the complete description of multiple-pair emissions that is needed for quantum communication analyses while reducing to the usual biphoton-state description at low generation rates.
PACS numbers42.65.Lm 03.65.Ud 03.67.Mn 42.50.Dv
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