| Two-photon interferometry is a relatively new field with applications ranging from precise measurements of optical phase shifts to fundamental tests of quantum mechanics. In contrast to conventional single-photon interferometry, two-photon interferometry typically involves measuring correlations between two detectors placed in two different output ports of an interferometer. Of particular interest is two-photon interferometry with entangled photon pairs, in which case it is often possible to observe effects that are not possible with classical fields. Because these entanglement effects are becoming increasingly important in Quantum Information Processing (QIP) applications, there is currently a strong need for further exploration of new ideas, basic physics, and experimental techniques of two-photon interferometry.;Contained herein are the results of three new two-photon interferometry experiments using entangled photon pairs produced by a Type-I Parametric Down-Conversion (PDC) source. In the first experiment, we demonstrate a new technique for compensating for two-photon interferometer beamsplitter asymmetries by manipulating the polarization degree of freedom in the system. Roughly speaking, projective polarization measurements are used to re-balance the magnitude of various two-photon amplitudes that were made distinguishable by non-ideal refection and transmission coefficients of a key beamsplitter. In the second experiment, we utilize a short coherence-length continuous-wave (CW) PDC pump laser to explore two-photon interferometry in a new intermediate regime between the more familiar extremal cases which use either a long coherence-length CW pump or an ultra-short pulsed pump laser. These results provide new insight into the role of PDC pump coherence in two-photon interferometry. Finally, we use two-photon interferometry to experimentally investigate entangled "photon holes", which is a new form of entanglement that arises from the correlated absence of photon pairs in an otherwise constant background. By using vastly unbalanced interferometers and well-defined timing, we observe nonclassical correlations due to "time-bin" entangled photon-hole states. |
