M. Pavicic, CLOSURE OF THE ENHANCEMENT AND DETECTION LOOPHOLES IN THE BELL THEOREM BY THE 4TH ORDER INTERFERENCE WITH PHOTONS OF DIFFERENT COLORS, Physics letters. A, 209(5-6), 1995, pp. 255-260
A loophole-free Bell experiment requiring detection efficiency as low
as 67% is proposed. The experiment uses different frequency photon int
erference of fourth order at an asymmetrical beam splitter and a resul
ting non-maximal entanglement.