In this thesis we investigate the relation between coherence and indistinguishability of photons in several quantum interference experiments. Some nonclassical phenomena which can only be explained in terms of quantum mechanics are investigated. We study the interpretation of the wave function and are led to conclude that the state reflects not only what is known, but sometimes what is knowable in principle.; In the spontaneous parametric down-conversion process, an incident pump photon splits into an entangled pair of signal and idler photons which are emitted simultaneously. We demonstrate that it is a quantum-mechanical process by performing an experiment in which a classical inequality is violated by about 600 standard deviations.; It is found that when the idler photons from two crystals are aligned so as to overlap, mutual coherence between the signal photons is induced by idler {dollar}isb1,{dollar} even though this beam from the first crystal does not induce additional emission at the second crystal. Furthermore, the degree of coherence between the signal photons can be controlled either by an attenuator or by a differential time delay placed in the idler connection between the two crystals, and this has no effect on the intensities of the signal beams. We demonstrate that the interference can be destroyed without any direct uncontrollable disturbance acted on the interfering photons. We conclude that the interference is always a manifestation of the intrinsic indistinguishability of the photon paths.; With the help of the technique of the induced coherence without induced emission we investigate the entanglement of signal and idler photons. We find that a delay inserted in the idler path has the same effect as one inserted in the signal path, even though only the signal photons interfere. This delay can be long or short compared to the coherence length of the signal photon. We also show that the normalized overlap integral of the idler photons represents not only the degree of indistinguishability of the idler photons, but also that of the signal photons.; Two experiments are carried out to test the de Broglie pilot wave theory, a hybrid of classical and quantum concepts. According to this theory, there exist both photons and electromagnetic waves, with the waves not only yielding the probabilities of photon detections, but having a physical existence as well. From the experimental results we find that the "empty wave", which has lost all photons, can neither give rise to photoelectric detection nor induce coherence effects. The statistical interpretation of the wave function proposed by Born remains the only valid means of accounting for the observed results.
展开▼
