Recent work using spontaneous parametric down-conversion (SPDC) has made possible investigations of the Einstein-Podolsky-Rosen paradox in its original (position-momentum) form. We propose an experiment that uses SPDC photon pairs to measure through which slit a photon passes while simultaneously observing double-slit interference.
An experiment on one-photon state localization in space using a correlation technique in Spontaneous Parametric Down Conversion (SPDC) process is discussed. Results of measurements demonstrate an idea of the Einstein-Podolsky-Rosen (EPR) paradox for coordinate and momentum variables of photon states. Results of the experiment can be explained with the help of an advanced wave technique. The experiment is based on the idea that two-photon states of optical electromagnetic fields arising in the nonlinear process of the spontaneous parametric down conversion (spontaneous parametric light scattering) can be explained by quantum mechanical theory with the help of a single wave function.
Full text: We present two experiments on single- and two-particle interference. In the single-photon interference experiment, photons from a spontaneous parametric down-conversion (SPDC) source are send through a double slit. An interference pattern is built up frame by frame from shots obtained with an EMCCD camera behind the slit. Each frame contains on average less than one photon, thus demonstrating true single-photon sensitivity of the camera. The build-up of the interference pattern nicely demonstrates the concept of wave-particle duality. In a next step, we describe the Heisenberg's lens experiment and present the conditions required to analyse and investigate the spatial correlations of momentum entangled photons produced by SPDC. The occurrence of double-slit interference now depends on the experimental arrangement for the second photon of the pair, for example: interference can only occur if the second photon is also passing a double slit. We present an analysis of such a double-double-slit experiment. (author)
We report a two-photon double-slit interference experiment. Two correlated photons, generated by spontaneous parametric downconversion and traveling in different directions, are made to pass through a double slit in such a way that the path of one photon can be identified with that of the other photon. No single-photon interference pattern is observed even if the path is not actually identified, but a spatial interference pattern appears in the joint detection counting rates of the photon pairs. It can easily be shown that these nonlocal phenomena cannot be exhibited by any kind of classical field.
We employ a photon pair created by spontaneous parametric down conversion (SPDC) where the pump laser is in the TEM01 mode to perform a Young's double-slit experiment. The signal photon illuminates the two slits and displays interference fringes in the far-field while the idler photon measured in the near-field in coincidence with the signal photon provides us with ‘which-slit’ information. We explain the results of these experiments with the help of an analytical expression for the second-order correlation function derived from an elementary model of SPDC. Our experiment emphasizes the crucial role of the mode function in the quantum theory of radiation.
Particle and wave like properties of photons can impressively be demonstrated in Young’s double slit experiment. Usually, measurements behind the slit provide information either about the path of the single photons or interference can be observed. Today the question of “which-slit” versus “interference” in the double-slit configuration is as relevant as it was in the early days of quantum mechanics. To gain deeper insight we set up an experiment using a pair of photons generated by SPDC pumped with a higher order mode (TEM 01 ). One of the SPDC photons, the signal photon, was used to illuminate the double slit and measure the single photon interference behind it. The other photon, the idler photon, was used in a reference measurement at the position of the slit using a polarizing beam splitter. First, the signal photons were obtained at the position of the slit as a function of the position of the entangled idler photons in a coincidence measurement. From this coincidence measurement the “which-slit” information is available. In a second coincidence measurement the far field interference fringes were obtained for signal photons passing through one of the slits, only, selected by the position of the reference detector measuring the entangled idler photons. The newest results will be presented and discussed. This may provide new insights in the wave-particle dualism and thus inspire the discussion about the nature of photons.