The quantum interference phenomenon was observed in Young’s double-slit experiment using a single photon, and then, the validity of quantum mechanics was demonstrated. However, the reason these fringes appear has not been completely explained yet because photon motion has not been investigated in detail. We found a method to observe the motion of photons using the properties of optical fibers and showed vector diagrams of the photon motion near the double-slit. The photons gradually changed their direction while intersecting and formed interference fringes. In addition, utilizing the mode property of the fiber, we observed fringes at its output end, even when one of the two interfering waves could not transmit through the fiber.
The quantum interference phenomenon was observed in Young’s double-slit experiment using a single photon, and then, the validity of quantum mechanics was demonstrated. However, the reason these fringes appear has not been completely explained yet because photon motion has not been investigated in detail. We found a method to observe the motion of photons using the properties of optical fibers and showed vector diagrams of the photon motion near the double-slit. The photons gradually changed their direction while intersecting and formed interference fringes. In addition, utilizing the mode property of the fiber, we observed fringes at its output end, even when one of the two interfering waves could not transmit through the fiber.
The investigation of the interference phenomenon of Young's double-slit using a single photon is an epoch-making experiment demonstrating the mystery of quantum mechanics, but the details have not yet been clarified. We have developed a method for observing the behavior of photons near the double-slit using a multimode optical fiber to obtain a two-dimensional map of photon motion. Quantitative analysis of the directional motion revealed that the directional change was related to the derivative of the electric field and was uniquely determined by the direction of photon motion.
Abstract Young’s double slit experiment revived the wave theory of the light. The standard interpretation is that the light behaves as waves before and after passing through the diaphragm of the double slit. Feynman called the double slit experiment the only mystery in quantum mechanics. Recently, the photon chamber has been proposed and utilized to study the behavior of photons near the detecting screen. The experiments show that the light, near the screen, behaves as photons propagating along the straight-line trajectories, and the trajectories distribute as waves. In this article, we utilize two new methods to study experimentally the patterns near the diaphragm of the double slit/cross double slit. The experiments show that, the first time, within certain macroscopic distance from the diaphragm, (1) the pattern is non-interference and thus, the light behaves as photons and produces the “particle pattern” near the double slit; and (2) both the shape and nature of the patterns are distance-dependent; when the distance increases, the non-interference pattern gradually evolves to the interference pattern. The experiments: (1) provide novel phenomena/data for further theoretical development of the optics and for understanding the nature of the light; and (2) show the Feynman’s mystery with different aspect.
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.
In classical optics, Young's double-slit experiment with colored coherent light gives rise to individual interference fringes for each light frequency, referring to single-photon interference. However, two-photon double-slit interference has been widely studied only for wavelength-degenerate biphoton, known as subwavelength quantum lithography. In this work, we report double-slit interference experiments with two-color biphoton. Different from the degenerate case, the experimental results depend on the measurement methods. From a two-axis coincidence measurement pattern we can extract complete interference information about two colors. The conceptual model provides an intuitional picture of the in-phase and out-of-phase photon correlations and a complete quantum understanding about the which-path information of two colored photons.
Young’s double slit experiments, which represent the mystery of quantum mechanics, have been interpreted by quantum probability waves and pilot waves. In this article, to study the mystery, we introduce the “virtual box” which represents the slide of double-slit and its right-hand neighborhood. Within, and only within, the “virtual box” the standard wave interference patterns are formed. We propose and carry out “comprehensive double slit experiments” that show that, first, light travelling from a laser source towards the slides of double slit and/or cross-double slit behaves as particle (postulate-1), and second, after leaving the "virtual box" zone and being directed towards the detector, the light behaves as a stream of photons (postulate-2) with no further interference due to the slits. On the one hand, the interference patterns do exist in the comprehensive-double slit experiments. On the other hand, we show four novel phenomena: (1) the fringes of the interference patterns are formed independently; (2) the fringes of the interference patterns can be formed partially; (3) the longitudinal shields do not disturb the interference patterns; and (4) the range of the virtual box is less than one inch. These novel phenomena indicate that photons behave as particles, and would not be expected if photons behave as waves created by the double slit and/or cross double slit. The comprehensive-double slit experiments show the coexistence of wave distribution and particle nature of photons in the same experiment, which violates complementarity principle and thus, seems a paradox. We suggest an interpretation to address the paradox. All observations of the comprehensive-double slit experiments are consistent. Progress in studying the mystery of the double slit experiment is presented.
3.1 Interference of a Single Photon The kinds of study originally conducted by Thomas Young - in particular, the celebrated "double slit" experiment that we briefly examined in Chapter 1 (see Fig. 1) - provide a capacity to reveal far more than the wave nature of light, important as that is. True enough, the observed characteristic fringe pattern, when monochromatic light passes through two closely spaced slits onto a screen, appears to be simply explicable on the basis of waves from each slit undergoing constructive and destructive interference at different positions on the screen. Yet, astonishingly, these patterns of interference are still exhibited when individual photons of a low-intensity input beam reach the screen one at a time, showing that it cannot in fact be a matter of different photons having to interfere with each other. Indeed, Dirac enunciated the general principle that photons can never directly interact with each other. The double slit and other such experiments indicate that each photon interacts in a delocalized, wave-like manner with both slits at the same time. Successive experiments build interference patterns that conform to an exact mathematical distribution formula, but the position at which an individual photon is detected in any particular instance cannot be predicted; this is a quintessential illustration of quantum uncertainty. Using the path integral approach of quantum theory, the phenomenon is more accurately represented by introducing a summation over all possible routes between the source and the screen on which the pattern appears, signifying an entire "lifetime" for each photon involved in the experiment. This relates to the fact that the actual trajectory is unknown without an observation, and thus we only obtain the probabilities of the photon striking the screen at different positions and times; all trajectories (potentialities) must be considered in a superposition. Each route is considered equally probable, and the variation in phase produces quantum interference. The differences in phase of each trajectory, at varying positions on the screen, generates the fringe pattern. An intriguing variation on this experiment involves "marking" the photons so that the actual route of each photon to the screen is known. Remarkably, in such a case, the fringe patterns do not appear because quantum interference cannot occur. A consequence of the observation of the photon route is an effect that, in other quantum mechanical connections, is known as a collapse of the wavefunction. However, it is possible for the fringe patterns to reappear when information on the route of the photons is lost; this is known as a quantum eraser.