Quantum teleportation: everything you wanted to know, but were afraid to ask

Two interesting things happened last in the field of quantum technology: Chinese scientists teleported photons of light from a ground station to a space satellite and the annual conference of leading experts in quantum physics was held in Moscow. Business Insider managed to catch Dr. Eugene Polzik from the Niels Bohr Institute, one of the leading experts in quantum teleportation, and question him about a variety of issues, including the outstanding success of his Chinese colleagues.

“Teleportations of this kind were carried out inlaboratory conditions since 1997, however, Chinese scientists managed to achieve this amazing technological effect at a great distance, ”said Polzik.

In 2012, a team of European scientists successfullyteleported photons between the two Canary Islands. Between the transmitting and receiving devices, the distance was 141 kilometers. The Chinese researchers managed to break this record in July, when they successfully teleported photons to a distance of more than 500 kilometers.

We have long dreamed of a similar technology fromStar Trek, although our intuition has always said that teleportation is in principle impossible. However, the physics of our real world, in which we dwell daily, is little similar to the physics of the world of quanta. Here the laws of a falling stone from a cliff and controlling electrons and individual photons of light are completely different from what we are used to seeing. Therefore, in such a bizarre world, almost everything is possible, including teleportation. How to figure it all out? Start with quantum entanglement.

What is quantum entanglement?

Sometimes two quantum particles turn out to bemirror-linked. Whatever happens to one of these particles, the same thing will happen to the other. Even if they are separated by large distances. They still remain two separate objects, but they are identical in everything. When two particles separate their states from one another, then such particles are called entangled.

“Suppose I created a couple of entangled photons,” Crawler explains.

“I leave one with me, and the other I send withusing a laser on a space satellite in orbit, hoping that the photon will reach its destination. Teleportation can be considered successful only when the state of entanglement of two photons is divided between the transmitting and receiving stations. ”

The main technical complexity of the processTeleportation is the transfer of a photon at a certain distance from an entangled particle-partner. In the case of the Chinese experiment, one photon was in a laboratory on Earth, and the second was successfully sent to an orbiting satellite. The changes that have occurred with the photon on Earth as part of the manipulations of scientists have also affected the photon in space - this is quantum teleportation in its purest form.

How to understand whether the satellite received the desired photon, and not some random particle of light?

This is relatively easy to do thanks toa process called spectral filtering. It allows scientists to identify and track individual photons of light, labeling them with a unique identification number.

“You know the frequency of the photon that yousend, you know its orientation. The satellite is directed to a source of origin located on Earth. If you have very good optical equipment on both sides, then this optics sees only the source, and nothing more, ”continues Polzik.

The spectral filtering method is indifferent to “noise” in the form of other photons. For example, during the same experiment in the Canary Islands, transmission was carried out in a clear sunny sky.

Millions of photons were transmitted to the satellite, but only 900 reached the destination. Why?

The further you try to send tangledphoton, the less effective this process becomes. Moreover, the Earth’s atmosphere is in constant motion, so losing photons along their path into outer space is easy.

“Even if there wasn’t an atmosphere, youit is still necessary to focus the beam of light so that it is aimed at the satellite. If you shine a laser pointer on the palm of your hand, then the point of light will be small, but just remove the laser and the point becomes larger - this is the law of diffraction, ”says Polzik.

From the earth, it is quite difficult for light to break through to space (to an optical receiver mounted on an orbiting satellite). It is greatly distorted, so most photons simply go nowhere.

“Successful teleportation is possible only ata very short time. In a general sense, this is very impractical, but nonetheless, ways to apply this technology can be found, ”continues Polzik.

Is quantum teleportation an instant data transfer capability?

Not really. Teleportable objects do not disappear, and then reappear somewhere else. Scientists use entanglement to transmit information about the quantum state of one photon to another. Without this information, the photon will have to physically cover the entire distance between the transmitter and receiver. And again, information is not transmitted instantly. This is possible only when the sender measures the quantum state of his photon, thereby changing the state of the photon at the receiver. Due to quantum entanglement, essentially one photon "becomes" another photon.

So what is all this for?

Quantum teleportation can prove the conceptthe possibilities of creating an ultra-secure global communication network. As a key to open a lock, a message transmitted over a quantum network will reach only the recipient who has a correctly entangled photon that will allow him to receive and read this message.

Albert Einstein once called quantumentanglement by “terrible long-range action”, but this long-range action is a fundamental component due to which everything works. And one day he can become the driver of our safe communication in the future.