In modern physics, the double slit experiment is a demonstration that light and matter can display the characteristics of classically defined waves and particles; In addition, it presents the fundamental nature of quantum-mechanical phenomena that are fundamentally probabilistic. The original experiments were performed by Davisson and Germer in 1927.
The first double-slit experiment was conducted by Thomas Young in 1801. His experiment was part of classical physics, long before quantum mechanics and the concept of wave-particle duality. He believes it shows that the theory of light waves is true, and his experiments are sometimes referred to as Young's or Young's slit .
Experiments include a general class of "double path" experiments, where the wave is divided into two separate waves which are then combined into a single wave. The change in the path length of the two waves produces a phase shift, creating an interference pattern. Another version is the Mach-Zehnder interferometer, which divides the file with a mirror.
In the basic version of this experiment, a coherent light source, such as a laser beam, illuminates a plate punctured by two parallel slits, and light passing through the gap is observed on the screen behind the plate. The nature of light waves causes light waves to pass through two gaps to interrupt, producing bright and dark bands on the screen - a result that would not be expected if light consists of classical particles. However, light is always found to be absorbed on the screen at discrete points, as individual particles (not waves), interference patterns emerging through the different densities of these particle hits on the screen. Furthermore, experimental versions that include detectors in the cracks found that any photons detected pass through a slit (like a classic particle), and not through cracks (like waves). However, the experiments show that the particles do not not form an interference pattern if it detects which cleft is passed. These results show the principle of wave-particle duality.
Other atom-scale entities, such as electrons, are found to exhibit similar behavior when fired in the direction of a double aperture. In addition, individual discrete impact detection is observed inherently probabilistic, which can not be explained using classical mechanics.
Experiments can be performed with entities much larger than electrons and photons, although that becomes more difficult as the size increases. The largest entity used for the double slit experiment is a molecule consisting of 810 atoms (whose total mass is more than 10,000 units of atomic mass).
The double-slit experiment (and its variation) has been the experiment of classical thinking, because of its clarity in expressing the core puzzle of quantum mechanics. Because it shows the fundamental limitations of the observer's ability to predict the results of his experiments, Richard Feynman calls it "an impossible [...] phenomenon to explain in the classical way, and which is in it the heart of quantum mechanics.In fact, it contains only the mystery [quantum mechanics]. "
Video Double-slit experiment
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If light consists only of ordinary or classical particles, and these particles are fired in a straight line through the gap and allowed to attack the screen on the other side, we would expect to see patterns corresponding to the size and shape of the gap. However, when the "single slit experiment" is actually done, the pattern on the screen is the diffraction pattern in which the light is spreading. The smaller the gap, the larger the spreading angle. The top of the picture shows the center of the pattern formed when the red laser illuminates the gap and, if one looks carefully, the two side bands fade. More bands can be viewed with smoother tools. Diffraction describes the pattern as a result of light wave interference from the gap.
If one illuminates the two parallel slits, the light from the two slits interrupts again. Here interference is a clearer pattern with alternating circuits of light and dark bands. Bandwidth belongs to the frequency of the light that shines. (See the photo below on the right.) When Thomas Young (1773-1829) first pointed to this phenomenon, it showed that light consists of waves, because the brightness distribution can be explained by the interruptive and subtractive additive interference of the wavefront. The Young Experiment, conducted in the early 1800s, played an important part in the acceptance of the wave theory of light, defeating the corpuscular theory of light proposed by Isaac Newton, which had been the model of light propagation received in the 17th and 18th centuries. However, the subsequent discovery of the photoelectric effect suggests that under different circumstances, light can behave as if composed of discrete particles. This seemingly contradictory discovery makes it necessary to go beyond classical physics and take into account the quantum nature of light.
Feynman likes to say that all quantum mechanics can be derived from mature thinking through the implications of this single experiment. He also proposes (as a mind experiment) that if the detector is placed before each gap, the interference pattern will be lost.
Englert-Greenberger's duality relationships provide detailed treatment of multiple gap maths in the context of quantum mechanics.
The first low intensity double-slice experiment was performed by G. I. Taylor in 1909, by reducing the incident light level until the incidence of photon emission/absorption was largely non-overlapping. The double slit experiment was not done with anything other than light until 1961, when Claus JÃÆ'¶nsson of the University of TÃÆ'¼bingen did so with an electron beam. In 1974, Italian physicist Pier Giorgio Merli, Gian Franco Missiroli, and Giulio Pozzi repeated experiments using single electrons and biprism (not slits), suggesting that each electron interferes with itself as predicted by quantum theory. In 2002, the single-electron experiment version was selected as "the most beautiful experiment" by readers of World Physics.
Maps Double-slit experiment
Experiment variation
Individual particle disturbance
An important version of this experiment involves single particles (or waves - for consistency, they are called particles here). Sending particles through a double-slit tool one by one produces a single particle to appear on the screen, as expected. Remarkably, however, interference patterns arise when these particles are allowed to build one by one (see adjacent drawings). This shows the wave-particle duality, which states that all matter exhibits the nature of waves and particles: particles are measured as single pulses in one position, while waves represent the possibility of absorbing particles in specific places on the screen.. This phenomenon has been shown to occur with photons, electrons, atoms and even some molecules, including buckyballs. So experiments with electrons add confirmatory evidence to the view that electrons, protons, neutrons, and even larger entities are usually called particles, but have their own wave properties and even wavelengths (related to their momentum).
The probability of detection is the square of the wave amplitude and can be calculated with the classical wave (see below). The particles did not reach the screen in a predictable sequence, so knowing where all the previous particles appeared on the screen and in what sequence did not tell where future particles would be detected. If there is wave cancellation at some point, that does not mean that a particle disappears; it will appear elsewhere. Since the beginning of quantum mechanics, some theorists have sought ways to include additional determinants or "hidden variables" which, if they are known, will explain the location of each individual impact with the target.
A more complicated system involving two or more particles in a superposition can not accept the above explanation.
"The path" of experiment and principle are complementary
A well-known experiment of the mind predicts that if the particle detector is positioned in the gap, indicating through the gap where the photon is running, the interference pattern will be lost. This experimental experiment describes the principle of complementarity that photons can behave as either particles or waves, but can not be observed as both at the same time. Regardless of the importance of this thought experiment in the history of quantum mechanics (eg, see discussion on Einstein's version of this experiment), technically feasible realizations of this experiment were not proposed until the 1970s. (A naive implementation of the experimental textbook is not possible because photons can not be detected without absorbing photons.) Currently, several experiments have been conducted that illustrate various aspects of complementarity.
An experiment conducted in 1987 produced results indicating that information could be obtained on which path the particle had taken without damaging the overall interference. This shows the measurement effects that disrupt the particles on the way to the lower levels and thus are influenced by interference patterns only at a comparable level. In other words, if one does not insist that the method used to determine the gap where each photon is skipped is truly reliable, one can still detect an interference pattern (degraded).
Pending options and quantum eraser variations
Wheeler's pending selection experiments show that extracting "which way" information after a particle passing through a gap can retroactively change the previous behavior in the gap.
Quantum eraser experiments show that wave behavior can be recovered by deleting or permanently making no "which way" information available.
A simple do-it-at-home demonstration of the quantum eraser phenomenon is given in an article in Scientific American. If a set of polarizers before each gap with their axis is orthogonal to each other, the interference pattern will be eliminated. Polarizer can be regarded as the introduction of path-to-each beam information. Introducing a third polarizer in front of the detector with a 45 ° axis relative to another polarizer "wipes" this information, allowing interference patterns to reappear. It can also be accounted for by taking light into classical waves, and also when using a circular pole and a single photon. Implementation of a polarizer using an entangled photon pair has no classical explanation.
Weak measurement
In an experiment published in 2012, researchers claim to have identified pathways that have taken every particle with no ill effects at all on the interference patterns generated by the particles. To do this, they use the settings in such a way that the particles coming to the screen do not come from a point-like source, but from sources with two maximum intensities. However, commentators such as Svensson have pointed out that there is actually no conflict between the weak measurements made in the variant of the double slit experiment and the Heisenberg uncertainty principle. Weak measurements followed by peg selection do not allow simultaneous positioning and momentum measurements for individual individual particles, but allow the measurement of the average path of the particles arriving at different positions. In other words, the researchers created a full-fledged landscape statistics map.
More variations
In 1967, Pfleegor and Mandel demonstrated the interference of two sources using two separate lasers as a light source.
It was shown experimentally in 1972 that in a double slit system in which only one opening was open at all times, the disturbance was observed by providing path difference in such a way that the detected photon could be derived from one of the slits. The experimental conditions are such that the photon density in the system is much less than unity.
In 1999, a double-slit experiment was successfully performed with buckyball molecules (each comprising 60 carbon atoms). A fairly large buckyball (diameter of about 0.7 m, almost half a million times larger than protons) to be seen under an electron microscope.
In 2005, E. R. Eliel presented an experimental and theoretical study of optical transmission of a thin perforated metal screen by two subwavelength gaps, separated by many optical wavelengths. The total intensity of the far-field double-slit pattern is shown to be reduced or increased as a function of the wavelength of incident light rays.
In 2012, researchers at the University of Nebraska-Lincoln conducted a double-slit experiment with electrons as described by Richard Feynman, using a new instrument that allows transmission control of two gaps and monitoring of single electron detection events. Electrons are fired by an electron gun and pass through one or two slits of 62Ã,m wide ÃÆ'â € "4Ã, m high.
In 2013, a double slit experiment was successfully performed with molecules consisting of 810 atoms (whose total mass is over 10,000 units of atomic mass).
Analog wave hydrodynamic pilot
Analogous hydrodynamics have been developed that can re-create various aspects of quantum mechanical systems, including the interference of one particle through a double slit. Droplets of silicone oil, bouncing along the liquid surface, self-propels through the interaction of resonance with its own wave field. The drip slowly empties the liquid with each reflection. At the same time, the ripples of the previous reflections affect the path. The interaction of droplets with their own ripples, which form what is known as a pilot wave, causes it to exhibit behaviors previously thought to be peculiar to elementary particles - including behavior that is customarily taken as evidence that the elementary particles are spreading through space like waves, without any specific location, measurable.
Behavior that mimics through this hydrodynamic pilot wave system includes the diffraction of a single quantum particle, tunneling, quantized orbit, orbital level separation, spin, and multimodal statistics. It is also possible to conclude the uncertainty relationship and the exclusion principle. Videos are available that illustrate the various features of this system. (See External links.)
However, a more complicated system involving two or more particles in superposition can not accept a simple and easily understood explanation. Thus, no hydrodynamic analogue attachment has been developed. However, optical analogs are possible.
Classical wave-optical formulation
Much of the behavior of light can be modeled using classical wave theory. The Huygens-Fresnel principle is one such model; It states that every point on a wavefront produces a secondary wavelet, and that interference at each subsequent point can be found by summing the contribution of each wavelet at that point. This sum needs to take into account the phases and amplitudes of each wavelet. It should be noted that only the intensity of the measured light field - this is proportional to the square of amplitude.
In a double-slit experiment, the two slits are illuminated by a single laser beam. If the gap width is small enough (less than the wavelength of the laser light), the gap breaks the light into a cylindrical wave. These two cylindrical wavefronts are superimposed, and their amplitude, and therefore their intensity, at any point in the composite wavefront depends on the magnitude and phase of the two wavefronts. The phase difference between two waves is determined by the difference in the distance traveled by the two waves.
If the large viewpoint is compared to the split of the gap (far field), the phase difference can be found by using the geometry shown in the figure below. The difference in the path between two waves moving at the angle of ? provided by:
Where d is the distance between two slots. When two waves are in phase, that is, the path difference equals the sum of the integral wavelengths, the amplitude is summed, and therefore the intensity is summed up, and when they are in the anti-phase, that is, the path difference equals half the wavelength, one half wavelength, , then the two waves cancel and the added intensity is zero. This effect is known as a nuisance. The maxima fracture interference occurs at an angle
dimana? adalah panjang gelombang cahaya. Jarak sudut dari fringes, ? f , diberikan oleh
Jarak dari frinji pada jarak z dari celah diberikan oleh
For example, if two gaps are separated by 0.5 mm ( d ), and illuminated with a wavelength laser of 0.6 m (? ) , then at 1m distance ( z ), the distance from the perimeter will be 1.2 mm.
Jika lebar celah b lebih besar dari panjang gelombang, persamaan difraksi Fraunhofer memberikan intensitas cahaya yang terdifraksi sebagai:
Where sinc function is defined as sinc ( x ) = sin ( x )/( x ) for x ? 0, and sinc (0) = 1.
This is illustrated in the above figure, where the first pattern is the diffraction pattern of the single gap, given by the sinc function in this equation, and the second illustrates the combined intensity of the diffracted light from the two gaps, the cos function represents fine structure, and the rough structure represents diffraction by the individual gap as described by the sinc function.
Similar calculations for the near field can be performed using the Fresnel diffraction equation. As the field of observation draws closer to the field where the gap is located, the diffraction pattern associated with each slit decreases, resulting in the area where the disturbance is reduced, and may disappear altogether when there is no overlap in the two diffracted patterns.
Interpretation of experiment
Like the SchrÃÆ'¶dinger cat thinking experiment, double-slit experiments are often used to highlight differences and similarities between the various interpretations of quantum mechanics.
Copenhagen interpretation
The Copenhagen interpretation, advanced by some pioneers in the field of quantum mechanics, asserts that it is undesirable to assume anything beyond the mathematical formula and the kind of physical equipment and reaction that allows us to gain knowledge of what is happening. on an atomic scale. One of the mathematical constructs that enable researchers to predict very accurately the results of certain experiments is sometimes called probability waves. In its mathematical form analogous to the description of physical waves, but "peaks" and "troughs" indicate the degree of probability for occurrence of certain phenomena (eg, sparks of light at a particular point on the detector screen) that can be observed in the macro world of ordinary human experience.
The probability of "wave" can be said to "pass through space" because the probability value that can be calculated from its mathematical representation depends on time. One can not talk about the location of any particle like a photon between the time it is transmitted and the time it is detected just because to say that something lies somewhere at a certain time we have to detect it. The requirement for the final appearance of the interference pattern is the emitted particles, and that there is a screen with at least two different paths for the particles taken from the emitter to the detection screen. The experiment did not observe anything between the particle emission time and its arrival on the detection screen. If subsequent ray tracking is made as if the light waves (as understood in classical physics) are wide enough to take both paths, then the rays will accurately predict the appearance of maxima and minima on the detector screen as many particles pass through the apparatus and gradually " paint "the expected interference pattern.
Path-integral formulation
The Copenhagen interpretation is similar to the integral formulation of the path of quantum mechanics provided by Feynman. The path integral formation replaces the classical idea of ​​a single unique path for a system, with the summing of all possible trajectories. Trajectories are added together using functional integration.
Setiap jalur dianggap memiliki kemungkinan yang sama, dan dengan demikian menyumbang jumlah yang sama. Namun, fase kontribusi ini pada suatu titik di sepanjang jalur ditentukan oleh tindakan di sepanjang jalur:
Semua kontribusi ini kemudian ditambahkan bersama, dan besarnya hasil akhir dikuadratkan, untuk mendapatkan distribusi probabilitas untuk posisi suatu partikel:
Seperti yang selalu terjadi ketika menghitung probabilitas, hasilnya kemudian harus dinormalkan dengan memaksakan:
To summarize, the probability distribution of results is the normalized quadrate of the superposition, above all the path from the origin to the end point, of the wave propagating to the action along each path. Differences in cumulative action along different paths (and thus relative phases of contribution) result in interference patterns observed by double-slit experiments. Feynman emphasizes that the formulation is only a mathematical description, not an attempt to describe the real process we can measure.
Relational interpretation
According to the relational interpretation of quantum mechanics, first proposed by Carlo Rovelli, such observations in the results of special double-slit experiments of the interaction between observers and observed objects (physically interacting with), there is no absolute property possessed by the object. In the case of electrons, if initially "observed" in a given gap, then the particle-particle interaction (photon-electron) includes information about the position of the electron. This partially limits the eventual location of the particles on the screen. If it is "observed" (measured by photons) not on a particular gap but on the screen, there is no "path" of information as part of the interaction, so that the "observed" position of the electrons on the screen is determined strictly by its probability function. This keeps the resulting pattern on the screen just as if each electron had passed through the two slits. It has also been argued that space and distance are relational, and that electrons can appear to be in "two places at once" - for example, in both slits - since the spatial relationships with certain points on the screen remain identical from the two gap locations.
Many world interpretations
Source of the article : Wikipedia
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