The Chinese for the first time in the world teleported photons from Earth to orbit (1400 km)

Many years ago, Albert Einstein called quantum entanglement "eerie action at a distance." This is truly a counterintuitive concept that, at first glance, contradicts common sense. Two objects can be at a great distance from each other, but they maintain a “connection” with each other through their quantum states. Having destroyed the state of one object (by measuring it), we thereby find out the state of the object entangled with it, no matter how far it is. That is, the quantum state of the first object at the moment of measurement moves to the second object, it is figuratively called quantum teleportation.

Now a group of Chinese physicists for the first time in the world has carried out a quantum teleportation of an object from Earth to orbit. The results of the experiment with "creepy action at a distance" publishedJuly 4, 2017 on the preprint site arXiv.org (arXiv: 1707.00934).

Especially for this experiment, the Chinese last year put the scientific satellite Micius into the sun-synchronous orbit. Every day it passes over the same point of the Earth at the same time, which makes it possible to carefully prepare the experiment and conduct it at any time under unchanged conditions, and also repeat if necessary under the same conditions. The Micius satellite is equipped with a highly sensitive photon detector and equipment for determining the quantum state of individual photons sent from the 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 in the range of quantum teleportation. Previously, such experiments were carried out only on Earth, and the maximum distance for checking quantum entanglement was about 100 km. In vacuum, the transfer of photons is more reliable, they react less with surrounding objects and are better entangled.

The Ngari station with a transmitter for the experiment was built in the mountains of Tibet at an altitude of more than 4000 m. The station generated intricate pairs of photons at a speed of 4000 per second. Half of them went to the orbital station, and there it was checked whether quantum confusion remained after the transmission. The second half of the photons remained on Earth.

To improve the quality of transmission, the researchers developed a number of innovative techniques and special devices, including a compact ultra-bright source of multiphoton entanglement, equipment to reduce beam divergence, and a high-speed and high-precision APT (acquiring, pointing, tracking) system.



Measurements showed that some of the photons upon arrival at the satellite did retain confusion with their terrestrial “partners”. In particular, for 32 days of transmission, out of several million sent photons, 911 remained confused. The transmission accuracy was 0.80 ± 0.01, which significantly exceeds the classical limit (see diagram below).


Photons with the same quantum states from the physical point of view are the same photons. Thus, it can be stated that scientists for the first time in history teleported an object from the surface of the Earth to orbit. Well, in a practical sense, this is the first working uplink for reliable transmission of quantum information over very long distances - from Earth to satellite. The authors believe that this is an important step towards the creation of quantum Internet on a global scale.

Theoretically, there is no maximum distance limit for measuring entanglement, that is, quantum teleportation. In practice, the quantum state of photons is very fragile and is destroyed as a result of a reaction with the environment, so it is very important to develop technologies for reliable transmission of entangled photons over long distances.

Quantum teleportation can find application in various fields: “Teleportation over long distances is considered a fundamental element in protocols, such as large-scale quantum networks and distributed quantum computing,” writes a group of Chinese scientists in an abstract to a scientific article. - 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 channel, which can conveniently connect two remotely distant points on Earth with a relatively small signal loss, because most of the path the photons travel in a vacuum.

It will now be difficult for other countries to break China’s record for quantum teleportation because neither the European Union nor the United States planned to launch satellites with photo detectors specifically for such an experiment in space, and it is incredibly difficult to maintain quantum entanglement on Earth in a 1,400 km fiber.