Physicists from Shanghai announced the successful completion of the first “space” quantum teleportation, transferring information about the state of a particle from the Mo Tzu quantum satellite to a tracking station on Earth, according to an article posted in the electronic library arXiv.org
“We announce the first quantum teleportation of single photons from an observatory on Earth to a satellite in low-Earth orbit, 1,400 kilometers away from it. The successful implementation of this task opens the way to ultra-long-range teleportation and is the first step towards the creation of a quantum Internet,” Jian writes. -Wei Pan (Jian-Wei Pan) from the University of Shanghai and his colleagues.
The phenomenon of quantum entanglement is the basis of modern quantum technologies. This phenomenon, in particular, plays an important role in secure quantum communication systems - such systems completely eliminate the possibility of unnoticed “wiretapping” due to the fact that the laws of quantum mechanics prohibit “cloning” the state of light particles. Currently, quantum communication systems are being actively developed in Europe, China, and the USA.
Behind last years Scientists from Russia and foreign countries have created dozens of quantum communication systems, the nodes of which can exchange data over fairly large distances, amounting to about 200-300 kilometers. All attempts to expand these networks internationally and intercontinentally have encountered insurmountable difficulties related to the way light fades as it travels through fiber optics.
For this reason, many teams of scientists are thinking about moving quantum communication systems to the “cosmic” level, exchanging information via satellite, allowing them to restore or strengthen the “invisible connection” between entangled photons. The first spacecraft of this kind is already present in orbit - it is the Chinese Mo Tzu satellite, launched into space in August 2016.
This week, Pan and his colleagues described the first successful quantum teleportation experiments carried out aboard the Mo-Zu and at a communications station in the town of Ngari in Tibet, built at an altitude of four kilometers to exchange information with the first quantum satellite.
Quantum teleportation was first described at a theoretical level in 1993 by a group of physicists led by Charles Bennett. According to their idea, atoms or photons can exchange information at any distance if they were “entangled” at the quantum level.
To carry out this process, a regular communication channel is required, without which we cannot read the state of entangled particles, which is why such “teleportation” cannot be used to transmit data over astronomical distances. Despite this limitation, quantum teleportation is extremely interesting to physicists and engineers because it can be used for data transmission in quantum computers and for data encryption.
Guided by this idea, scientists entangled two pairs of photons in a laboratory in Ngari, and transferred one of the four “entangled” particles aboard the Mo-Dza using a laser. The satellite simultaneously measured the state of both this particle and another photon, which was on board at that moment, as a result of which information about the properties of the second particle was instantly “teleported” to Earth, changing the way the “ground” photon, confused with the first, behaved particle.
In total, as Chinese physicists say, they managed to “entangle” and teleport over 900 photons, which confirmed the correctness of the “Mo-Zu” work and proved that two-way “orbital” quantum teleportation is possible in principle. In a similar way, as scientists note, it is possible to transmit not only photons, but also qubits, memory cells of a quantum computer, and other objects of the quantum world.
Numerous blockbusters of recent years, most of them film adaptations of comic books, have firmly implanted in the consciousness modern man superhero image. A superhero is most often an ordinary-looking person who has supernatural powers and often forced because of this to lead a secretive lifestyle. These films are so popular, colorful and numerous that for some people the concept of “superhero” has become commonplace. The idea of the reality of such heroes visits people more and more often - that’s why stories such as teleportation in China appear and are very popular.
Superman on the roadway
In the fall of 2012, one of the main hits of the World Wide Web was a video that allegedly showed more than just teleportation 
person, but a very dramatic teleportation of two people at once. The video posted on the YouTube video hosting site is about a minute long and looks like footage 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 location of the events is one of the urban or suburban intersections of China. Main characters three. The first is a truck driver with a van white, the second is a cyclist. The third is a mysterious stranger whose face is not visible because of his wide hood. In terms of physique, this clearly young man could be either a boy or a girl.
The events in the video unfold as follows. After several cars have passed, a truck appears in the background, gradually picking up speed. As he approaches, a cyclist appears from a darkened area on the side road on the left. 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, some movement is noted: a rapid blurred silhouette is approaching the site of the impending collision. At the last moment, the silhouette is outlined more clearly and the viewer sees a man who grabs the cyclist almost under the very wheels of the car. After this, the stranger, the cyclist and the bicycle literally disappear, and the truck begins to brake. The car has not yet completely stopped when a group of two people and a bicycle appears on the far right side of the screen, just on the illuminated part of the road. The stranger lets go of the rescued man, while his hands glow brightly. He throws his hood over his head and quickly moves out of the way. At this time, the clearly shocked cyclist sits down exhausted on the curb, and a truck driver comes out and finds nothing on the roadway.
It is easy to deceive those who are happy to be deceived
The teleportation of a person 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. Immediately, lively discussions began about whether the video was real or whether it was a hoax 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 original “fan fiction” arose immediately - stories began to be invented designed to create the story of a female superhero (the female gender of the character seemed more intriguing and impressive to most audiences), to reveal the reasons that prompted her to hide her superpowers, and the like.
But there were also a lot of skeptic critics, and they literally broke down the video to its bones. Many rational arguments were given 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 fatal accident was alarming: contrary to usual, the truck, when approaching the intersection, began to pick up speed rather than slow down, as if creating the conditions for a dramatic scene. The cyclist’s suspicion is also suspicious: he surprisingly calmly rode directly under the wheels, without changing speed and without even turning his head when crossing the main road, where he should give way to traffic priority. Not everything is all right with the truck driver - the footage clearly shows that the man who got out of the cab is wearing a bright white T-shirt or shirt. But in a fairly well-lit cabin during braking, not only is nothing bright visible, the driver is not visible there at all.
As for the mysterious man with the ability to teleport himself and teleport others, he is also not so “pure”. Firstly, there are obvious traces of video editing in his “energy trail” during his super-fast dash onto the road. His silhouette at the moment of grabbing the cyclist is very clear, while the blurry silhouette of his movement still remains. Secondly, the choice of teleportation end point looks very strange. The laws of geometry, physics and simply logic say that the simplest and most natural thing would be for the rescued cyclist to move in the direction of the stranger’s movement - that is, in left side screen, get out of the way. But teleportation occurs with a 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, glowing hands the savior and his removal into the darkness, it suits best. The totality of all these observations and reasoning leads to the conclusion that this teleportation is quite creative, but still a hoax.
Alexander Babitsky
MOSCOW, July 12 - RIA Novosti. Physicists from Shanghai announced the successful completion of the first “space” quantum teleportation, transferring information about the state of a particle from the Mo Tzu quantum satellite to a tracking station on Earth, according to an article posted in the electronic library arXiv.org
“We announce the first quantum teleportation of single photons from an observatory on Earth to a satellite in low-Earth orbit, 1,400 kilometers away from it. The successful implementation of this task opens the way to ultra-long-range teleportation and is the first step towards the creation of a quantum Internet,” Jian writes -Wei Pan (Jian-Wei Pan) from the University of Shanghai and his colleagues.
The phenomenon of quantum entanglement is the basis of modern quantum technologies. This phenomenon, in particular, plays an important role in secure quantum communication systems - such systems completely eliminate the possibility of unnoticed “wiretapping” due to the fact that the laws of quantum mechanics prohibit “cloning” the state of light particles. Currently, quantum communication systems are being actively developed in Europe, China, and the USA.
In recent years, scientists from Russia and foreign countries have created dozens of quantum communication systems, the nodes of which can exchange data over fairly large distances, amounting to about 200-300 kilometers. All attempts to expand these networks internationally and intercontinentally have encountered insurmountable difficulties related to the way light fades as it travels through fiber optics.
For this reason, many teams of scientists are thinking about moving quantum communication systems to the “cosmic” level, exchanging information via satellite, allowing them to restore or strengthen the “invisible connection” between entangled photons. The first spacecraft of this kind is already present in orbit - it is the Chinese Mo Tzu satellite, launched into space in August 2016.
This week, Pan and his colleagues described the first successful quantum teleportation experiments carried out aboard the Mo-Zu and at a communications station in the town of Ngari in Tibet, built at an altitude of four kilometers to exchange information with the first quantum satellite.
Quantum teleportation was first described at a theoretical level in 1993 by a group of physicists led by Charles Bennett. According to their idea, atoms or photons can exchange information at any distance if they were “entangled” at the quantum level.
To carry out this process, a regular communication channel is required, without which we cannot read the state of entangled particles, which is why such “teleportation” cannot be used to transmit data over astronomical distances. Despite this limitation, quantum teleportation is extremely interesting to physicists and engineers because it can be used for data transmission in quantum computers and for data encryption.
Guided by this idea, scientists entangled two pairs of photons in a laboratory in Ngari, and transferred one of the four “entangled” particles aboard the Mo-Dza using a laser. The satellite simultaneously measured the state of both this particle and another photon, which was on board at that moment, as a result of which information about the properties of the second particle was instantly “teleported” to Earth, changing the way the “ground” photon, confused with the first, behaved particle.
In total, as Chinese physicists say, they managed to “entangle” and teleport over 900 photons, which confirmed the correctness of the “Mo-Zu” work and proved that two-way “orbital” quantum teleportation is possible in principle. In a similar way, as scientists note, it is possible to transmit not only photons, but also qubits, memory cells of a quantum computer, and other objects of the quantum world.
In the summer of 2016, Chinese scientists will conduct the world's first experiment on quantum teleportation over a distance of more than 1,200 kilometers. Nature News reports this.
For the experiment, scientists plan to launch a satellite in June 2016. Thus, physicists hope to realize quantum teleportation of particle states between space and ground stations.
At the first stage of the experiments, scientists are going to test the reliability of cryptographic communication between Beijing and Vienna, in which a near-Earth satellite will act as an intermediary.
At the second stage, scientists will carry out quantum teleportation of photons via satellite between stations in Delinghe and in Lijiang (or Nanshan). The distance between points exceeds 1200 kilometers.
Quantum teleportation is the transfer of a quantum state over a distance using a spatially separated coupled (entangled) pair and a classical communication channel, in which the state is destroyed at the point of departure during a measurement, after which it is recreated at the point of reception. The term was established thanks to an article published in 1993 in the journal “Physical Review Letters”, which describes what kind of quantum phenomenon is proposed to be called “teleportation” (eng. teleporting) and how it differs from the “teleportation” popular in science fiction. Quantum teleportation does not transfer energy or matter over a distance. A mandatory step in quantum teleportation is the transfer of information between the points of departure and reception via a classical, non-quantum channel, which can be carried out no faster than at the speed of light, thereby not violating the principles of modern physics.
When implementing quantum teleportation, in addition to transmitting information via a quantum channel, it is also necessary to transmit additional information necessary to read the message via a classical channel. To transmit the “quantum part”, the Einstein-Podolsky-Rosen correlations characteristic of quantum entangled particles are used, and any ordinary communication channel is suitable for transmitting classical information.
For simplicity, let us consider a quantum system with two possible states \psi_1 and \psi_2 (for example, the projection of the spin of an electron or photon onto a given axis). Such systems are often called qubits. However, the method described below is suitable for transferring the state of any system that has a finite number of states.
Let the sender have particle A, located in an arbitrary quantum state \psi_A = \alpha \psi_1 + \beta \psi_2, and he wants to transfer this quantum state to the recipient, that is, make sure that the recipient has at his disposal particle B in the same very condition. In other words, it is necessary to convey the ratio of two complex numbers \alpha and \beta (with maximum accuracy). Note that the main goal here is to convey information not as quickly as possible, but as accurately as possible. To achieve this goal, the following steps are followed.
The sender and receiver agree in advance to create a pair of quantum entangled particles C and B, with C going to the sender and B to the receiver. Since these particles are entangled, each of them does not have its own wave function (state vector), but the entire pair (or rather, the degrees of freedom that interest us) are described by a single four-dimensional state vector \psi_(BC).
A quantum system of particles A and C has four states, but we cannot describe its state with a vector - only a system of three particles A, B, C has a pure (fully defined) state. When the sender makes a measurement that has four possible outcomes on a system of two particles A and C, he receives one of 4 eigenvalues of the measured quantity. Since during this measurement a system of three particles A, B, C collapses into some new state, and the states of particles A and C become completely known, cohesion is destroyed and particle B finds itself in some specific quantum state.
It is at this moment that a “transfer” of the “quantum part” of information occurs. However, restore transmitted information not yet possible: the recipient knows that the state of particle B is somehow connected with the state of particle A, but does not know exactly how!
To figure this out, it is necessary for the sender to inform the receiver via the usual classical channel of the result of its measurement (spending two bits corresponding to the engaged state AC measured by the sender). According to the laws of quantum mechanics, it turns out that, having the result of a measurement carried out on a pair of particles A and C, plus particle B entangled with C, the recipient will be able to perform the necessary transformation on the state of particle B and restore the original state of particle A.
Complete transfer of information will take place only after the recipient has the data received through both channels. Before the result is received over the classical channel, the recipient cannot say anything about the transmitted state.
The fantastic concept of teleportation comes from a specific interpretation of the experiment: “the initial state of particle A is destroyed after everything that has happened. That is, the state was not copied, but transferred from one place to another.”
Experimental implementation
The experimental implementation of quantum teleportation of the polarization state of a photon was carried out in 1997 almost simultaneously by groups of physicists led by Anton Zeilinger (University of Innsbruck) and Francesco de Martini (University of Rome).
In the journal Nature on June 17, 2004, the successful experimental observation of quantum teleportation of the quantum state of an atom was announced by two research groups: M. Riebe et al., Nature 429, 734-737 (teleportation of the quantum state of a calcium ion) and M. D. Barrett et al. ., Nature 429, 737-739 (teleportation of a qubit based on a beryllium atom ion). Despite the media hype, these experiments can hardly be called a breakthrough: rather, they are just another big step towards the creation of quantum computers and the implementation of quantum cryptography.
In 2006, teleportation was carried out for the first time between objects of different nature - laser radiation quanta and cesium atoms. A successful experiment was carried out research group from the Niels Bohr Institute in Copenhagen.
On January 23, 2009, scientists for the first time managed to teleport the quantum state of an ion one meter.
On May 10, 2010, in an experiment carried out by physicists from the University of Science and Technology of China and Tsinghua University, the quantum state of a photon was transmitted over 16 kilometers.
In 2012, Chinese physicists managed to transmit 1,100 entangled photons over a distance of 97 kilometers in 4 hours.
In September 2012, physicists from the University of Vienna and the Austrian Academy of Sciences set a new record in quantum teleportation - 143 kilometers
In September 2015, scientists from the US National Institute of Standards and Technology managed to teleport photons over optical fiber over a distance of over 100 km. The experiment used a single-photon detector with molybdenum silicide superconducting cables at temperatures close to absolute zero.
Years ago, Albert Einstein called quantum entanglement “spooky action at a distance.” This is a truly counterintuitive concept that at first glance defies common sense. Two objects may be at a great distance from each other, but they maintain a “connection” with each other through their quantum states. By destroying the state of one object (by measuring it), we thereby find out the state of the object entangled with it, no matter at what distance it may be. That is, the quantum state of the first object at the moment of measurement, as it were, passes to the second object; this is figuratively called quantum teleportation.
Now a group of Chinese physicists has, for the first time in the world, carried out quantum teleportation of an object from Earth to orbit. The results of the “spooky action at a distance” experiment were published on July 4, 2017 on the preprint website arXiv.org (arXiv:1707.00934).
Especially for this experiment, the Chinese launched the Micius scientific satellite into a sun-synchronous orbit last year. Every day it passes over the same point on the Earth at the same time, which makes it possible to carefully prepare the experiment and carry it out at any time under constant conditions, and also repeat it if necessary under the same conditions. The Micius satellite is equipped with a highly sensitive photon detector and equipment to determine the quantum state of individual photons sent from Earth.
During the experiment, quantum teleportation was carried out with varying degrees of reliability (see diagram) at a distance of 500-1400 km from the transmitter to the satellite, which is a new world record for the range of quantum teleportation. Previously, such experiments were carried out only on Earth, and the maximum distance to test quantum entanglement was about 100 km. In a vacuum, photons are transmitted more reliably, they react less with surrounding objects and retain entanglement better. 
The Ngari station with the transmitter for the experiment was built in the mountains of Tibet at an altitude of more than 4000 m. The station generated entangled pairs of photons at a speed of 4000 per second. Half of them were sent to an orbital station, and there they checked whether quantum entanglement was preserved after transmission. The second half of the photons remained on Earth.
To improve transmission quality, researchers have developed a number of innovative techniques and special instruments, including a compact ultra-bright multiphoton entanglement source, equipment to reduce beam divergence, and a high-speed and high-precision APT (acquiring, pointing, tracking) system.
Measurements showed that some photons, upon arrival at the satellite, actually remained entangled with their terrestrial “partners.” In particular, over 32 days of transmission, out of several million sent photons, 911 remained entangled. The transmission accuracy was 0.80 ± 0.01, which significantly exceeds the classical limit (see diagram below).
Photons with identical quantum states are identical photons from a physical point of view. Thus, it can be stated that for the first time in history, scientists teleported an object from the surface of the Earth into orbit. Well, in a practical sense, this is the first working uplink for the reliable transmission of quantum information over very long distances - from Earth to a satellite. The authors believe that this is an important step towards creating a quantum internet on a global scale.
Theoretically, there is no maximum distance limit for measuring entanglement, i.e. quantum teleportation. In practice, the quantum state of photons is very fragile and is destroyed as a result of reaction with the environment, so it is very important to develop technologies for reliable transmission of entangled photons over long distances.
Quantum teleportation could find application in different areas: “Long-distance teleportation is considered a fundamental element in protocols such as large-scale quantum networks and distributed quantum computing,” a group of Chinese scientists wrote in the abstract of the scientific paper. - To create a “quantum Internet” on a global scale, it is necessary to significantly expand the distance for transmitting information. A promising technology for this is the use of a satellite platform and satellite communication link, which can conveniently link two remotely located points on Earth with relatively little signal loss because photons travel most of the way in a vacuum.
It will now be difficult for other countries to break China's record for quantum teleportation range, because neither the European Union nor the United States planned to launch satellites with photodetectors specifically for such an experiment in space, and maintaining quantum entanglement on Earth in a 1,400 km long optical fiber is incredibly difficult.
