Two-slit Interference Research Articles

Understanding Modified Two-Slit Experiments Using Path Markers

Some modified two-slit interference experiments were carried out showing an apparent paradox in wave–particle duality. In a typical such experiment, the screen, where the interference pattern is supposed to be formed, is replaced by a converging lens. The converging lens forms the images of the two slits at two spatially separated detectors. It was claimed that each of these two detectors give information about which slit a photon came from, even though they come from the region of interference. These experiments generated a lot of debate. The various refutations pointed out that the controversial claims involved some questionable assumptions. However the refutations were largely philosophical in nature, and one may like to substantiate those with arguments which are testable, at least in principle. Here such an experiment is theoretically analyzed by introducing path markers which are two orthogonal polarization states of the photon. Analyzing the polarization at the two detectors shows that the photons which give rise to interference, and reach a particular detector, always come from both the slits. This provides clarity in understanding such experiments by making use of testable quantum correlations.

Single-mode lasing in an AlGaInAs/InP dual-port square microresonator.

Mode selection is crucial to achieving stable single-mode lasing in microlasers. Here, we demonstrate experimentally a dual-port square microresonator for single-mode lasing with a side-mode-suppression ratio (SMSR) exceeding 40 dB. By connecting waveguides at two opposite vertices, the quality factor for the antisymmetric mode (ASM) is much higher than that of the symmetric mode (SM), enabling single-mode lasing. Furthermore, far-field interference patterns similar to Young's two-slit interference are observed. This microlaser is capable of providing two optical sources simultaneously for optical signal processing in high-density integrated photonic circuits.

The Aharonov–Bohm effect in a closed flux line

The Aharonov–Bohm (AB) effect was convincingly demonstrated using a micro-sized toroidal magnet but it is almost always explained using an infinitely-long solenoid or an infinitely-long flux line. The main reason for this is that the formal treatment of the AB effect considering a toroidal configuration turns out to be too cumbersome. But if the micro-sized toroidal magnet is modelled by a closed flux line of arbitrary shape and size then the formal treatment of the AB effect is exact, considerably simplified, and well-justified. Here we present such a treatment that covers in detail the electromagnetic, topological, and quantum-mechanical aspects of this effect. We demonstrate that the AB phase in a closed flux line is determined by a linking number and has the same form as the AB phase in an infinitely-long flux line which is determined by a winding number. We explicitly show that the two-slit interference shift associated with the AB effect in a closed flux line is the same as that associated with an infinitely-long flux line. We emphasise the topological nature of the AB phase in a closed flux line by demonstrating that this phase is invariant under deformations of the charge path, deformations of the closed flux line, simultaneous deformations of the charge path and the closed flux line, and the interchange between the charge path and the closed flux line. We also discuss the local and nonlocal interpretations of the AB effect in a closed flux line and introduce a non-singular gauge in which the vector potential vanishes in all space except on the surface surrounded by the closed flux line, implying that this vector potential is zero along the trajectory of the charged particle except on the crossing point where this trajectory intersects the surface bounded by the closed flux line, a result that questions the alleged physical significance of the vector potential and thereby the local interpretation of the AB effect.

Two-particle superposition effects in two-slit interference

Entanglement can modify the interference patterns of multi-particle systems. We analyse, using the path integral formalism, a novel example of multi-particle interference and some unexplored aspects of this phenomenon by considering the two-slit arrangement with two distinguishable particles in a superposition state. The two components of entanglement, multiplicity of multi-particle terms and their coherence, can be studied separately by comparing the patterns of product, mixed and superposition states. This suggests a scheme to detect multi-particle superposition in some favourable cases. Moreover, the dependence of the effect on the entanglement degree, measured by the Schmidt number, is not a monotone.

Nature of interference between Autler–Townes peaks in generic multi-level system

In this work we present a theoretical frame work to identify the role and the nature of interference between Autler-Townes (AT) peaks (or dressed states) in generic multi-level system. The destructive interference between the AT peaks, gives rise to sharp transparency window known as electromagnetically induced transparency (EIT). In the three-level system, the two AT peaks interferes pair-wise with each other, almost similar to the two-slit interference. In the four-level system, the interference between the three AT peaks is also pair-wise analogous to three-slit interference but has a bit more complicated nature of interference. However, in many practical situations in atomic systems only the simple form of interference similar to three-level system dominates. In the three-level system, the nature of interference (i.e. constructive, destructive or zero/no interference) between the two AT peaks is purely determined by the natural decay rate of the states coupled by the control laser. However, in four-level system the nature of interference between the two extreme AT peaks can be tuned from constructive to destructive by tuning the power of the control laser.

Demystifying the delayed-choice quantum eraser

The delayed-choice quantum eraser has long been a subject of controversy, and has been looked at as being incomprehensible to having retro-causal effect in time. Here the delayed-choice quantum eraser is theoretically analyzed using standard quantum mechanics. Employing a Mach–Zehnder interferometer, instead of a conventional two-slit interference, brings in surprising clarity. Some common mistakes in interpreting the experiment are pointed out. It is demonstrated that in the delayed mode there is no which-way information present after the particle is registered on the screen or the final detectors, contrary to popular belief. However, it is shown that another kind of path information is present even after the particle is registered in the final detectors. The registered particle can be used to predict the results of certain yet to be made measurements on the which-way detector. This novel correlation can be tested in a careful experiment. It is consequently argued that there is no big mystery in the experiment, and no retro-causal effect whatsoever.

Josephson Junctions with Artificial Superparamagnetic Barrier: A Promising Avenue for Nanoscale Magnetometry

In this work, we realize a physical system---nanoengineered singly connected Josephson junction with a periodic superparamagnetic $\mathrm{Ni}/\mathrm{Al}$ multilayer---that manifests supercurrent-versus-magnetic field response typical of a dc superconducting quantum interference device (SQUID); however, unlike a SQUID, which involves a superconducting loop occupying significant space, our lumped device is more suitable for miniaturization. In addition, we show that it exhibits enhanced magnetic field sensitivity as compared with conventional superconductor-insulator-superconductor Josephson junctions. SQUID-like oscillatory response to external magnetic fields, analogous to the two-slit optical interference, is explained in terms of the dominance of Andreev bound states localized at the barrier edges in the comparatively thick and strongly anisotropic weak links. Our results may lead to significant advancement in development of nanoscale magnetic sensing techniques applicable to individual molecules or magnetic nanoparticles.

Probing the dephasing time of crystals via spectral properties of high-order harmonic generation

Coherent time is a characteristic time in the extreme nonlinear optics regime and thus generally introduced as the dephasing time in the simulations of the solid-state high-harmonic generation. This characteristic time linked with the coherent decay of quantum trajectory controls the emergence of the spectral splittings in the high harmonic spectroscopy, which can been attributed to the temporal interference between two adjacent harmonic emission channels. To reproduce the harmonic peaks and spectral splittings, a temporal two-slit interference model in the momentum space is introduced. In addition, mechanisms of spectral splitting provide a state-of-the-art avenue to probe the characteristic elapse between electron and hole. Based on the subfemtosecond resolution of the spectral interference opening and closing zones in the wavelength-dependent high-order harmonic spectra, we also propose an alternative scheme to probe the dephasing time of crystals by the feasible laser pulses in present experimental setups.

Computer model of the two-pinhole interference experiment using two-dimensional Gaussian wave-packets

The two-slit interference experiment has been modeled a number of times using Gaussian wave-packets and the Bohm–de Broglie causal interpretation. Here we consider the experiment with pinholes instead of slits and model the experiment in terms of two-dimensional Gaussian wave-packets and the Bohm–de Broglie causal interpretation.

Path predictability and quantum coherence in multi-slit interference

In an asymmetric multislit interference experiment, a quanton is more likely to pass through certain slits than some others. In such a situation one may be able to predict which slit a quanton is more likely to go through, even without using any path-detecting device. This allows one to talk of path predictability. It has been shown earlier that for a two-slit interference, the predictability and fringe visibility are constrained by the inequality . Generalizing this relation to the case of more than two slits is still an unsolved problem. A new definition for predictability for multi-slit interference is introduced. It is shown that this predictability and quantum coherence follow a duality relation , which saturates for all pure states. For the case of two slits, this relation reduces to the previously known one.

Exciton Gas Transport through Nanoconstrictions.

An indirect exciton is a bound state of an electron and a hole in spatially separated layers. Two-dimensional indirect excitons can be created optically in heterostructures containing double quantum wells or atomically thin semiconductors. We study theoretically the transmission of such bosonic quasiparticles through nanoconstrictions. We show that the quantum transport phenomena, for example, conductance quantization, single-slit diffraction, two-slit interference, and the Talbot effect, are experimentally realizable in systems of indirect excitons. We discuss similarities and differences between these phenomena and their counterparts in electronic devices.

A Computer Simulation for Quantal Interference

Interference of particles is one of the central phenomena of quantum mechanics. The computer program InterferenceSimulator demonstrates two-slit Fresnel interference patterns with one, the other, or both slits open. A magnetic flux situated between the two slits allows the demonstration of the Aharonov–Bohm effect. Simulations with short de Broglie wavelengths illustrate the classical limit of quantum mechanics. Because of the universality of wave phenomena, this program also demonstrates the geometrical-optics limit of wave optics for small wavelengths.

Wave-particle duality in asymmetric beam interference

It is well known that in a two-slit interference experiment, acquiring which-path information about the particle, leads to a degrading of the interference. It is argued that path-information has a meaning only when one can umabiguously tell which slit the particle went through. Using this idea, two duality relations are derived for the general case where the two paths may not be equally probable, and the two slits may be of unequal widths. These duality relations, which are inequalities in general, saturate for all pure states. Earlier known results are recovered in suitable limit.

Which-way measurement and momentum kicks

The two-slit interference experiment with a which-way detector has been a topic of intense debate. The scientific community is divided on the question whether the particle receives a momentum kick because of the process of which-way measurement. It is shown here that the same experiment can be viewed in two different ways, depending on which basis of the which-way detector states one chooses to look at. In one view, the loss of interference arises due to the entanglement of the two paths of the particle with two orthogonal states of the which-way detector. In another view, the loss of interference can be interpreted as arising from random momentum kicks of magnitude received by the particle, d being the slit separation. The same scenario is shown to hold for a three-slit interference experiment. The random momentum kicks for the three-slit case are of two kinds, of magnitude . The analysis is also generalized to the case of n-slit interference. The two alternate views are described by the same quantum state, and hence are completely equivalent. The concept of “local” vs. “nonlocal” kicks, much discussed in the literature, is not needed here.

Ontological Clarity via Canonical Presentation: Electromagnetism and the Aharonov-Bohm Effect.

Quantum physics demands some radical revision of our fundamental beliefs about physical reality. We know that because there are certain verified physical phenomena—two-slit interference, the disappearance of interference upon monitoring, violations of Bell’s inequality—that have no classical analogs. But the exact nature of that revision has been under dispute since the foundation of quantum theory. I offer a method of clarifying what the commitments of a clearly formulated physical theory are, and apply it to a discussion of some options available to account for another non-classical phenomenon: the Aharonov–Bohm effect.

Wave equation for the energy and the momentum of a moving particle

The conserved momentum and the energy of a moving particle obey a wave equation and have the wave feature. The moving particle acts as a point source of the waves. This nature is applied to explain the self-interference of an electron in Young’s two-slit interference experiment and the material dispersion. Material dispersion is associated with the rest mass of a photon in a medium.

Ultrahigh-accuracy measurement of refractive index curves of optical materials using interferometry technology

A spectral-domain white-light interferometry and a two-slit laser interference system for measurement of the refractive index curves of optical materials over a wide wavelength range was reported. The interferometry was employed to measure the group refractive index of the materials. An integral algorithm was proposed to calculate the refractive index curve from the obtained group refractive index. The integration required the refractive index value for a specific wavelength which could be achieved by the two-slit laser interference system. A spectrum correction method was used for calculation of group optical path difference. The proposed method realized an ultrahigh accuracy measurement of refractive index curve better than 0.0002, making it attractive for the application in the determination of optical parameters of new materials.

Evidence of a 6.12×1018 GeV Particle: Detection and Mathematics

In a new approach the graviton is defined as the field particle of spacetime rather than the mediator of gravity. The unification equation is derived and used to predict that for a freely falling body, the energy of incident gravitons is $6.12\times 10^{18}$ GeV. Redshift and scattering of gravitons should produce diffraction patterns, galactic halos and expansion of the Universe. The energy of incident gravitons remains constant as the Universe evolves because of the Doppler shift as bodies fall towards redshifted gravitons. Complex space is used to represent gravitons and explain Young’s two-slit interference. The approach is corroborated by empirical data and extends establish theory.

Quantum eraser for three-slit interference

It is well known that in a two-slit interference experiment, if the information, on which of the two paths the particle followed, is stored in a quantum path detector, the interference is destroyed. However, in a setup where this path information is "erased", the interference can reappear. Such a setup is known as a quantum eraser. A generalization of quantum eraser to a three-slit interference is theoretically analyzed. It is shown that three complementary interference patterns can arise out of the quantum erasing process.

Feynman’s lecture utilizing the Aharonov–Bohm effect

Volume II of The Feynman Lectures on physics is primarily devoted to explicating classical electromagnetism. Quantum theory arises in just one lecture, 15-5, entitled “The vector potential and quantum mechanics”. He emphasizes a remarkable conceptual change that the classically central notion of force “becomes quite secondary—if it is there at all” in quantum physics. He wishes to demonstrate, with as little quantum theory apparatus as possible, how the quantum notion of a wave function’s phase carries information about the classical force. To that end, he uses the Aharonov–Bohm effect in two thought experiments involving a two-slit electron interference pattern and two different configurations of magnetic field. Here I review Feynman’s argument with the benefit of more specificity about the quantum calculation than Feynman wished to give. Tiwari (Phys Rev Lett 113:158901, 2014, Quantum Stud.: Math. Found. 4:1 2017) recently criticized Feynman’s lecture for not providing a classical explanation of the Aharonov–Bohm effect. I believe this criticism is unwarranted because Feynman never set out to do that. What Feynman does is consider a two-slit interference experiment for an electron with a special magnetic field configuration, and he shows in this case that, when the magnetic field is turned on, the interference pattern on the detection screen shifts by the same distance as the classical trajectories emanating from the slit shift due to the magnetic force. That there is such an example, although unique, which suggests how the quantum phase may be connected to the classical trajectory, appears to be all that Feynman wishes to convey. If Feynman’s presentation is to be faulted, it is that this example is unique, that reasonable extensions of this thought experiment do not show this connection.