An ultrabright narrowband source of polarization-entangled photon pairs

The signals and idlers from a pair of matched, doubly resonant optical para metric amplifiers (OPAs) can be combined to yield polarization-entangled ve ctor signal and idler beams. Within any coincidence interval much longer th an the OPA cavity lifetime, every signal photon of polarization (i) over ri ght arrow is accompanied by an idler photon of the conjugate polarization ( i) over right arrow', and vice versa. For periodically poled lithium tantal ate OPAs, the pair production rate is estimated to be approximately 1.5 x 1 0(6) s(-1), within a 30 MHz bandwidth at a 795 nm centre wavelength and a 7 0 ns duration coincidence interval, using only 0.7 mW of pump power per OPA .