Information transfer faster than the speed of light. Building a telecommunication system
In the modern world, communication systems play an important role in the development of our world. Information channels literally entangle our planet, linking various information networks into a single global network the Internet. The brave world of modern technology includes advanced discoveries of science and technology, not rarely associated with the amazing possibilities of the quantum world. It can be said with confidence that today quantum technologies have become firmly established in our life. Any mobile equipment in our pockets is equipped with a memory chip, working using quantum charge tunneling. This technical solution allowed Toshiba engineers to build in 1984 a floating gate transistor, which became the basis for the construction of modern memory microcircuits. Every day we use similar devices, without thinking about what their work is based on. And while physicists are puzzled trying to explain the paradoxes of quantum mechanics, technological development is adopting the amazing possibilities of the quantum world.
In this article we will look at the interference of light, and analyze the methods of constructing a communication channel for instantaneous transmission of information using quantum technologies. Although many believe that it is impossible to transmit information faster than the speed of light, with the right approach, even such a task becomes solvable. I think you can see for yourself.
Introduction
Surely many people know about the phenomenon called interference. A beam of light is directed to an opaque screen with two parallel slits, behind which a projection screen is installed. The peculiarity of the slots is that their width is approximately equal to the wavelength of the emitted light. The projection screen produces a whole series of alternating interference fringes. This experiment, first conducted by Thomas Jung, demonstrates the interference of light, which became the experimental evidence of the wave theory of light at the beginning of the 19th century.
It is logical to assume that the photons must pass through the slits, creating two parallel bands of light on the rear screen. But instead, on the screen, a plurality of stripes are formed, in which light and darkness alternate. The fact is that when light behaves like a wave, each slot is a source of secondary waves. In places where secondary waves reach the screen in one phase, their amplitudes are added, which creates maximum brightness. And where the waves are in antiphase - their amplitudes are compensated, which creates a minimum of brightness. Periodic changes in brightness when applying secondary waves creates interference fringes on the screen.
But why does light behave like a wave? In the beginning, scientists suggested that photons might collide with each other and decide to release them one by one. Within an hour, an interference pattern appeared again on the screen. Attempts to explain this phenomenon led to the assumption that the photon is divided, passes through both slits, and colliding with itself forms an interference pattern on the screen.
The curiosity of scientists did not give rest. They wanted to know what slit the photon was really going through, and decided to observe. To uncover this mystery, detectors were placed in front of each slit, recording the passage of a photon. In the course of the experiment, it became clear that the photon passes only through one slit, either through the first or the second. As a result, two parallel bands of light were formed on the screen, without a hint of interference. Observation of photons destroyed the wave function of light, and photons began to behave like particles! As long as photons are in quantum uncertainty, they propagate like waves. But when they are observed, the photons lose their wave function and begin to behave like particles.
Further, the experiment was repeated once more, with the detectors turned on, but without recording the data on the photon motion trajectory. Despite the fact that the experience completely repeats the previous one, except for the possibility of obtaining information, after a while the interference pattern of light and dark stripes reappeared on the screen.
It turns out that it is not any observation that is influenced, but only one in which you can get information about the trajectory of photons. And this confirms the following experiment, when the trajectory of the photons is not tracked with the help of detectors installed in front of each slit, but with the help of additional traps that can be used to restore the trajectory of movement without interfering with the original photons.
Quantum eraser
Let's start with the simplest scheme (this is exactly the schematic image of the experiment, and not the actual installation scheme).
Send the laser beam to a translucent mirror (PP) . Usually such a mirror reflects half of the light falling on it, and the other half passes through. But photons, being in a state of quantum uncertainty, falling on a semi-transparent mirror, choose both directions simultaneously. Then, each beam reflected by mirrors (1) and (2) hits the screen, where we observe interference fringes. Everything is simple and clear: photons behave like waves.
Now we will try to understand which paths the photons went through — the top or the bottom. To do this, we will install down-converters (DC) on each path. A down converter is a device that, when a single photon hits it, produces 2 photons at the output (each with half the energy), one of which hits the screen ( signal photon ), and the second enters the detector (3) or (4) ( idle photon ). After receiving the data from the detectors, we will know which path each photon traveled. In this case, the interference pattern disappears, because we have learned exactly where the photons passed, and therefore destroyed quantum uncertainty.
Next, we complicate the experiment a little. Put reflecting mirrors in the path of each “idle” photon and direct them to the second translucent mirror (to the left of the source in the diagram). The passage of the second translucent mirror erases the information on the trajectory of the idle photons and restores the interference (according to the scheme of the Mach Zehnder interferometer). No matter which of the detectors work, we will not be able to find out which path the photons traveled. With this intricate scheme, we erase information about the choice of the path and restore quantum uncertainty. As a result, an interference pattern will be displayed on the screen.
If we decide to push the mirrors, the “ idle ” photons will again hit the detectors (3) and (4) , and as we know, the interference pattern on the screen will disappear. This means that by changing the position of the mirrors, we can change the displayed picture on the screen. So you can use this to encode binary information.
You can simplify the experiment a little and get the same result by moving the semi-transparent mirror in the path of "idle" photons:
As we see, “idle” photons travel more distance than their partners, which fall on the screen. It is logical to assume that if the image on the screen is formed earlier, then the resulting picture should not correspond to whether we determine the trajectory of photons or erase this information. But practical experiments show the opposite - no matter the distance, the image on the screen always corresponds to the actions performed with idle photons. According to information from wikipedia :
The main result of the experiment is that it does not matter whether the erasing process was performed before or after the photons reached the detector screen.A similar experience is also described in the book by Brian Green, The Fabric of the Cosmos and Space . This seems incredible, changing cause-effect relationships. Let's try to figure out what's what.
Some theory
If we look at Einstein's special theory of relativity as the speed increases, time slows down, according to the formula:
The speed of light is the limiting value, so for the particles of light (photons) themselves, time slows down to zero. It is more correct to say for photons there is no time, for them there is only the current moment in which they are at any point of their trajectory. This may seem strange, because we are accustomed to believe that light from distant stars reaches us after millions of years. But with the ISO of particles of light, photons reach the observer at the same point in time, as soon as they are emitted by distant stars.
The fact is that the present time for fixed objects and moving objects may not coincide. To represent time, it is necessary to consider space-time in the form of a continuous block stretched in time. The slices forming the block are the present tense moments for the observer. Each slice represents a space at one time from its point of view. This moment includes all points of space and all events in the universe, which are presented to the observer as occurring simultaneously.
Depending on the speed of movement, the present time slice will divide the space-time from different angles. In the direction of movement, the slice of the present time is shifted to the future. In the opposite direction, the current time slice is shifting into the past.
The greater the speed of movement, the greater the angle of cut. At the speed of light, the slice of the present time has a maximum angle of displacement of 45 °, at which time stops and the photons are in the same moment of time at any point of their path.
A reasonable question arises: how can a photon simultaneously be located at different points in space? Let's try to figure out what happens to space at the speed of light. As you know, as the speed increases, the effect of relativistic length reduction is observed, according to the formula:
It is not difficult to notice that at the speed of light any length in space will be compressed to zero size. So, in the direction of the photon movement, the space is compressed into a small point of Planck dimensions, at which the very concept of space-time disappears. It can be said that there is no space for photons, since their entire trajectory in the space with the photon's ISO is at one point.
So, now we know that regardless of the distance traveled, signal and idle photons simultaneously reach the screen and the detectors, since from the point of view of the photons there is neither time nor space. Given the quantum coupling of signal and idle photons, any impact on one photon will instantly affect the state of its partner. Accordingly, the picture on the screen should always correspond to whether we determine the trajectory of the photons or erase this information. This provides the potential for instant information transfer. One has only to note that the observer does not move at the speed of light, and therefore the picture on the screen must be analyzed after idle photons reach the detectors.
Practical implementation
Let us leave the theory to the theorists and return to the practical part of our experiment. To get the picture on the screen you will need to turn on the light source and direct the flow of photons to the screen. Information coding will occur at a remote object, by moving a translucent mirror in the path of idle photons. It is assumed that the transmitting device will encode information at equal time intervals, for example, transmit each data bit for a hundredth of a second.
You can use a sensitive digital matrix as a screen to directly record alternating changes. Then the recorded information must be deferred until the idle photons reach their destination. After that, you can begin to analyze the recorded information one by one in order to obtain the transmitted information. For example, if the encoder is on Mars, then the analysis of information must be started with a delay of ten to twenty minutes (exactly as long as it takes to light to reach the red planet). Despite the fact that the analysis of information is performed with a lag of tens of minutes, the information obtained will correspond to what is transmitted from Mars at the current time. Accordingly, a laser rangefinder will have to be installed along with the receiving device in order to accurately determine the time interval from which to start analyzing the transmitted information.
It is also necessary to take into account that the environment has a negative impact on the transmitted information. With the passage of photons through the airspace, a process of decoherence occurs, increasing the interference in the transmitted signal. In order to eliminate the influence of the environment as much as possible, it is possible to transmit signals in airless space using communication satellites.
Having organized two-way communication, in the future it is possible to build communication channels for instant information transfer to any range that our spacecraft can reach. Such channels of communication will be simply necessary if prompt access to the Internet outside of our planet is required.
PS There is one question that we have tried to pass by: what happens if we look at the screen before idle photons reach the detectors? Theoretically (from the point of view of Einstein's theory of relativity), we should see the events of the future. Moreover, if idle photons were reflected from a far-away mirror and brought them back, we could know our own future. But in reality, our world is much more mysterious, therefore, it is difficult to give the correct answer without conducting practical experiments. Perhaps we will see the most likely option for the future. But as soon as we receive this information, the future may change and an alternative branch of events may arise (according to the hypothesis of the multiworld interpretation of Everett). Or maybe we will see a mixture of interference and two bands (if the picture is made up of all possible options for the future).
Continuation of the article ->
Useful links:
Walborn, SP (2002). "Double-Slit Quantum Eraser". Phys. Rev. A 65
Delayed choice quantum eraser. The experiment of Kim et al. (1999)
Quantum eraser experiment
Speech by Tom Campbell
Quantum eraser proposed by Scully and Druhl
Source: https://habr.com/ru/post/410265/