Heisenberg's uncertainty principle explains single slit diffraction1 where maximum is always at the centre. The same experiment has been conducted but with transparent walls i.e. the material present on either side of the slit, instead of opaque material. The observed result is a minimum at the centre in between two maximum. It is intuitive that atleast some photons passed through the slit must end up at the centre of the diffraction pattern but the result is different. The diffraction pattern occurs as the photons interact with the material around the slit. While uncertainty principle cannot give quantitative explanation as the photons confined in gap between slits still occupy the same space whether it is passing through a slit or not. This paper discusses various experiments and results by examining the interactions between photons and the material of the wall which makes the slit for better understanding of properties of light.
Heisenberg's uncertainty principle explains single slit diffraction1 where maximum is always at the centre. The same experiment has been conducted but with transparent walls i.e. the material present on either side of the slit, instead of opaque material. The observed result is a minimum at the centre in between two maximum. It is intuitive that atleast some photons passed through the slit must end up at the centre of the diffraction pattern but the result is different. The diffraction pattern occurs as the photons interact with the material around the slit. While uncertainty principle cannot give quantitative explanation as the photons confined in gap between slits still occupy the same space whether it is passing through a slit or not. This paper discusses various experiments and results by examining the interactions between photons and the material of the wall which makes the slit for better understanding of properties of light.
This experiment investigates the Heisenberg Uncertainty Principle (HUP) through an optical analogue using Single-slit diffraction of a monochromatic He–Ne laser. The spatial confinement of light through slits of varying width is compared with the resulting diffraction patterns, providing a means to examine the relationship between position uncertainty ∆x and transverse momentum uncertainty ∆px. Diffraction patterns were recorded using a photodiode detector, and the angular positions of the first minima were determined and used to estimate the spread in momentum via the de-Broglie relation. The results demonstrates and are consistent with the expected inverse relationship. The measured diffraction patterns were also found to adhere to the Fraunhofer diffraction relation, supporting the validity of the experimental model and the goodness of fit of the data.The calculated uncertainty products were further found to be consistent with the expected magnitude of Planck's constant. and therefore the the findings support the interpretation of diffraction as a classifcal manifestation of the Foruier relation between position and momentum space. Thus providing a physically intuituve demonstration of Heisenberg's Uncertainty Principle.
We construct proper microscopic propositions to consistently capture and explain the interference patterns obtained for electrons and photons, detected individually or otherwise, in one- and two-slit experiments. We propose that for single-photon detections (after time integration), no interference pattern is obtained if one uses non-transparent slit material with slit holes (not diffraction slits). The non-transparent slit material does not permit photons to transmit, reflect internally nor refract. However, the same slit holes can produce the usual interference pattern with electromagnetic waves due to interfering in-phase and out-of-phase light waves. As for the electrons, detected individually or not, partial interference patterns can always be obtained from the two-slit experiment when one of the slits is closed (one at a time), which then can be manually overlapped to produce the complete interference pattern of a double-slit experiment. These new theoretically constructed experimental results for photons and electrons can be readily verified with our current technology using suitable optically non-transparent (for photons) and highly insulating (for electrons) slit materials.
We construct proper microscopic propositions to consistently explain the interference patterns obtained for electrons and photons in well-defined one- and two-slit experiments. Our propositions are also made explicit on the basis of quantum mechanics with proper quantitative analysis to support the correctness of the physical mechanisms proposed herein, which obey the wave-particle duality. In particular, our propositions and theoretical analysis demonstrate that for single-photon detection (after time integration), we cannot produce interference pattern if the usual diffraction slits are replaced with slit holes such that the non-transparent slit material does not permit photons to transmit, reflect internally or refract. However, the said non-transparent slit material with slit holes can produce the usual interference pattern with electromagnetic waves.
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.
A thought experiment, in which a light beam is sent through slits of different sizes thereby producing a diffraction pattern, is used to illustrate the uncertainty principle. Attempts to reduce the uncertainty in the measurement of the position of the light beam ( ) succeed, but at the expense of increasing the uncertainty in the measurement of the momentum ( ), so that the product of the two magnitudes, x, is still larger than h, Planck's constant. This experiment introduces the idea that one can know the value of a physical observable with as high a precision as necessary, but the act of measuring this observable has an effect on how much we can know about another observable. This thought experiment can be physically performed using a diode laser and a series of slits. A derivation is presented to relate the uncertainties in position and momentum to variables that can be measured with a ruler in a classroom or laboratory. Data from a typical experiment are also presented.