Quantum teleportation experiments successfully completed in China and Canada

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In China and Canada, experiments have been successfully carried out to conduct quantum teleportation over a distance of more than eight kilometers. These experiments in the conditions of the city were carried out independently by scientists from the two countries.

According to the South China Morning Post, previously such experiments were carried out only in the laboratory. Quantum teleportation is the transmission over a distance of a quantum state of matter, which is destroyed at the sending point and then recreated at the receiving point without a direct transfer of the particle itself.

A group of researchers from the University of Science and Technology of China has teleported photons over a distance of 12.5 km in the city of Hefei (east China's Anhui province). For this, conventional fiber optic networks were used.

Canadian scientists conducted a similar experiment in the city of Calgary (southwestern province of Alberta) at a distance of 8.2 km.

The specialists of the two countries used different approaches. The Chinese, through their channel, teleported only two photons per hour, but with higher reliability. The Canadians, on the other hand, were able to transmit up to 17 particles per minute, but their technology is less accurate and has a number of limitations for practical use.

Last year, American scientists managed to send a photon over a distance of more than 100 km, but only within the laboratory - through a fiber optic cable wound in turns there, reports

Numerous blockbusters of recent years, most of which are adaptations of comics, have firmly planted the image of a superhero in the consciousness of modern man. A superhero is most often an ordinary-looking person who has supernatural powers and is often forced to lead a secretive lifestyle because of this. These films are so popular, colorful and numerous that for some people the concept of "superhero" becomes commonplace. The idea of ​​the reality of such heroes visits people more and more often - therefore, such plots as teleportation in China appear and are very popular.

Superman on the road

In the fall of 2012, one of the main hits on the World Wide Web was a video that allegedly recorded not just a human teleportation, but a very dramatic teleportation of two people at once. The video posted on YouTube video hosting has a duration of about a minute and looks like shooting from a street surveillance camera. The time of events, judging by the timing in the upper left corner, is just after midnight on May 9, 2012. The place of events is one of the urban or suburban intersections of China. There are three main actors. The first is a driver of a truck with a white van, the second is a cyclist. The third is a mysterious stranger, whose face is not visible because of the wide hood. In terms of physique, this clearly young man can be both a boy and a girl.

The events in the video unfold as follows. After several passing cars, a truck appears in the background, gradually picking up speed. As he approaches, a cyclist emerges from a darkened area to the left along a side road. The trajectories and speeds of the truck and the cyclist are such that a collision seems inevitable, and the consequences for the driver of a lighter vehicle promise to be fatal. But here in the right darkened area of ​​the screen there is some movement: a swift, blurry silhouette is approaching the place of the impending collision. At the last moment, the silhouette is outlined more clearly and the viewer sees a man who grabs a cyclist almost under the very wheels of the car. After that, the stranger, the cyclist and the bike literally disappear, and the truck begins to brake. The car has not yet come to a complete stop when, on the far right side of the screen, just on the illuminated part of the road, a group of two people and a bicycle appears. The stranger releases the rescued, while his hands glow brightly. He throws a hood over his head and hurries out of the way. At this time, a visibly shaken cyclist sits down on the curb without strength, a truck driver who has come out and finds nothing on the roadway is heading towards him.

It is easy to deceive those who are glad to be deceived

Human teleportation in China, especially recorded on video and in addition under such cinematic circumstances, very quickly became known and gained millions of views on video hosting. Lively discussions immediately began as to whether the video was real or whether it was a prank by some visual effects specialists. It is curious that there were quite a lot of supporters of the reality of the teleportation observed on the set. Even peculiar “fanfictions” immediately arose - plots began to be invented to create the story of a superhero girl (the female character seemed more intriguing and impressive to the majority of the audience), to reveal the reasons that prompted her to hide her superpowers and the like.

But there were a lot of skeptical critics, and they literally decomposed the video into bones. A lot of rational arguments were made in favor of the fact that the plot is staged, bears obvious traces of the use of software for converting video material, and also has obvious logical flaws. First of all, the very occurrence of a potentially deadly accident alerted: contrary to custom, the truck, when approaching the intersection, did not slow down, but pick up speed, as if creating conditions for a dramatic scene. The suspicion of the cyclist is also suspicious: he rode surprisingly calmly right under the wheels, not changing speed and not even turning his head when crossing the main road, where he must give way to traffic priority. Not everything is in order with the truck driver - the footage clearly shows that the person who got out of the cab is dressed in a bright white T-shirt or shirt. But in a fairly well-lit cabin during braking, not only is nothing bright visible, there is no driver at all.

As for the mysterious person with the ability to teleport himself and teleport others, he is not so "clean" either. First, there are obvious traces of video editing in its "energy trail" during an ultra-fast dash to the road. His silhouette at the moment of grabbing the cyclist is very distinct, while the blurred silhouette of his movement is still preserved. Secondly, the choice of the end point of teleportation looks very strange. The laws of geometry, physics and just logic say that the easiest and most natural thing would be to move the rescued cyclist in the direction of the stranger - that is, to the left side of the screen, away from the road. But teleportation happens with the reverse vector, to the right - it turns out that the stranger made a kind of loop during teleportation, which has no explanation. Secondly, a vague doubt creeps in that the appearance of two teleporting people and a bicycle on the right side of the road is explained, so to speak, by stage necessity. It is this part that is the most illuminated in the entire scene, so to achieve the greatest drama, to observe the shock state of the rescued, the luminous hands of the savior and his removal into darkness, it is best suited. The totality of all these observations and reasoning leads to the conclusion that this teleportation is quite creative, but still a hoax.

Alexander Babitsky

Last year, a Long March 2D rocket took off from the Gobi Desert and put the Mo Tzu satellite into orbit in synchronism with the Sun, so it makes its way around the Earth every day. Mo Tzu is a highly sensitive satellite designed to transmit quantum information. It can detect the quantum states of individual photons released from the surface of our planet.

Today, the Mo Tzu team announced their unique achievement: they have succeeded in creating the first ground-to-ground satellite quantum network. This network was used to teleport the first object in history from Earth into its orbit. Teleportation is carried out by scientists who have conducted experiments in the field of optical physics. This process is based on the strange phenomenon of entanglement, during which two photons form a single point in time and space. From a technical point of view, they are described by a single wave function.

A feature of quantum entanglement is that these two photons exist at the same point, even if there are kilometers between them. Thus, a change in the state of one instantly affects the state of the other. Back in the 90s of the last century, scientists realized that they could use this phenomenon to teleport objects from one point of the Universe to another.

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The idea is to "load" information into one photon, then the other becomes identical to the first. This is teleportation

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Such experiments have been carried out many times in laboratory conditions on Earth, but this is the first time they have been tested in interstellar space. Teleportation is of great importance for a whole range of technologies related to quantum networks and computing.

In fact, there is no maximum distance for teleportation of photons, but the connection created between them is too fragile and can be destroyed due to foreign matter that has appeared in the atmosphere or in the optical fiber. To confirm their theory, scientists conducted experiments all the time at a greater distance, and now they went into orbit. True, for this it was necessary to build a station in Tibet at an altitude of 4 thousand meters.

As part of the experiment, entangled pairs of photons were created, which were launched at a speed of 4000 m/s

She conducted a satellite experiment on the transfer of quantum states between pairs of entangled photons (the so-called quantum teleportation) over a record distance of more than 1200 km.

The phenomenon (or entanglement) arises when the states of two or more particles are interdependent (correlated), which can be separated over arbitrarily long distances, but at the same time they continue to "feel" each other. The measurement of the parameter of one particle leads to the instant destruction of the entangled state of the other, which is difficult to imagine without understanding the principles of quantum mechanics, especially since the particles (it was specially shown in experiments to violate the so-called Bell inequalities) do not have any hidden parameters that would store information about the state of the “companion”, and at the same time, an instantaneous state change does not lead to a violation of the causality principle and does not allow useful information to be transmitted in this way.

To transmit real information, the participation of particles moving at a speed not exceeding the speed of light is additionally necessary. For example, photons having a common progenitor can act as entangled particles, and, say, their spin is used as a dependent parameter.

The transfer of states of entangled particles over increasingly long distances and under the most extreme conditions is of interest not only to scientists involved in fundamental physics, but also to engineers designing secure communications. It is believed that the phenomenon of entanglement of particles in the future will provide us with, in principle, unhackable communication channels. "Protection" in this case will be the inevitable notification of the participants in the conversation that someone else has interfered with their connection.

Evidence of this will be the unbreakable laws of physics - the irreversible collapse of the wave function.

Prototypes of devices for implementing such secure quantum communication have already been created, but there are also ideas to compromise the operation of all these “absolutely secure channels”, for example, by reversible weak quantum measurements, so it is still unclear whether quantum cryptography will be able to get out of the prototype testing stage, not whether all developments will be doomed in advance and unsuitable for practical application.

Another point: the transmission of entangled states has so far only been carried out over distances not exceeding 100 km, due to photon losses in the optical fiber or in the air, since the probability that at least some of the photons will reach the detector becomes vanishingly small. From time to time there are reports of another achievement on this path, but it is not yet possible to cover the entire globe with such a connection.

So, earlier this month, Canadian physicists announced successful attempts to communicate via a secure quantum channel with an aircraft, but it was only 3-10 km from the transmitter.

The so-called quantum repeater protocol is recognized as one of the ways to radically improve signal propagation, but its practical value remains in question due to the need to solve a number of complex technical issues.

Another approach is precisely to use satellite technology, since the satellite can remain in line of sight at the same time for different very distant places on Earth. The main advantage of this approach may be that most of the photon path will be in almost vacuum with almost zero absorption and the elimination of decoherence (coherence violation due to the interaction of particles with the environment).

To demonstrate the feasibility of satellite experiments, Chinese experts conducted preliminary ground-based tests that demonstrated successful bidirectional propagation of entangled photon pairs through an open environment at distances of 600 m, 13 km and 102 km with an effective channel loss of 80 dB. Experiments were also carried out on the transfer of quantum states on moving platforms under conditions of high losses and turbulence.

After detailed feasibility studies with the participation of Austrian scientists, a $ 100 million satellite was developed, launched on August 16, 2016 from the Jiuquan Cosmodrome in the Gobi Desert using the Long March 2D launch vehicle into an orbit with an altitude of 500 km.

The satellite was named "Mo-tzu" in honor of the ancient Chinese philosopher of the 5th century BC, the founder of Moism (the doctrine of universal love and state consequentialism). For several centuries in China, Mohism successfully competed with Confucianism, until the latter was adopted as the state ideology.

The Mozi mission is supported by three ground stations: in Delinghe (Qinghai Province), Nanshan in Urumqi (Xinjiang) and the GaoMeiGu Observatory (GMG) in Lijiang (Yunnan Province). The distance between Delinghe and Lijiang is 1203 km. The distance between the orbiting satellite and these ground stations varies between 500-2000 km.

Because entangled photons cannot simply be "amplified" like classical signals, new methods had to be developed to reduce attenuation in the transmission channels between Earth and satellites. To achieve the required coupling efficiency, it was necessary to simultaneously achieve the minimum beam divergence and high-speed and high-precision pointing to the detectors.

Having developed an ultra-bright cosmic source of two-photon entanglement and high-precision APT (acquiring, pointing, and tracking) technology, the group established a “quantum coupling” between pairs of photons separated by 1203 km, scientists conducted the so-called Bell test to check for violations of locality (the ability to instantly affect the state of a remote particles) and obtained a result with a statistical significance of four sigma (standard deviations).

Scheme of the photon source on the satellite. The thickness of the KTiOPO4 (PPKTP) crystal is 15 mm. A pair of off-axis concave mirrors focuses the pump laser (PL) at the center of the PPKTP crystal. The output of the Sagnac interferometer uses two dichromatic mirrors (DM) and filters to separate the signal photons from the pump laser. Two additional mirrors (PI) remotely controlled from the ground are used to fine-tune the beam direction for optimal beam collection efficiency. QWP - quarter-wave phase section; HWP - half-wave phase section; PBS - polarizing beam splitter.

Compared to previous methods using the most common commercial samples of telecommunications fiber, the efficiency of a satellite connection turned out to be many orders of magnitude higher, which, according to the authors of the study, opens the way for practical applications previously unavailable on Earth.