W. Tittel et al., NONLOCAL 2-PHOTON CORRELATIONS USING INTERFEROMETERS PHYSICALLY SEPARATED BY 35 METERS, Europhysics letters, 40(6), 1997, pp. 595-600
An experimental demonstration of quantum-correlations is presented. En
ergy and time entangled photons at wavelengths of 704 and 1310 nm are
produced by parametric downconversion in KNbO3 and are sent through op
tical fibers into a bulk-optical (704 nm) and an all-fiber Michelson-i
nterferometer (1310 nm), respectively. The two interferometers are loc
ated 35 meters aside from one another. Using Faraday mirrors in the fi
ber interferometer, all birefringence effects in the fibers are automa
tically compensated. We obtained two-photon fringe visibilities of up
to 95% from which one can project a violation of Bell's inequality by
8 standard deviations. The good performance and the auto-aligning feat
ure of Faraday-mirror interferometers show their potential for a futur
e test of Bell's inequalities in order to examine quantum correlations
over long distances.