TOWARD AN OPTICAL EVIDENCE OF QUANTUM INTERFERENCE BETWEEN MACROSCOPICALLY DISTINCT STATES

Thus far, all proposals for an optical evidence of macroscopic quantum interference have been frustrated by the low detector efficiencies. T wo innovations permit such an evidence with currently available equipm ent. We refer to the generation scheme of entangled states by parametr ic amplification proposed by S. Song, C. M. Caves, and B. Yurke [Phys. Rev. A 41, 5261 (1990)]. Setting a low gain for the parametric amplif ier introduces a drastic cutoff in the generated photon-number probabi lities that compensates for the broadening of the detection probabilit y in the first detector. Furthermore, we supplement the final homodyne detector with a degenerate type-I parametric amplifier which brings n earer the two previously distant states of the superposition. The avai lability of optical superposition states with large separation suggest s a practical way of transforming them into entangled coherent states associated with different paths, thus providing a new convenient sourc e for a ''which path'' experiment. [S1050-2947(98)08011-1].