Quantum teleportation: what it is and how it works

Quantum teleportation: what it is and how it works
Quantum teleportation: what it is and how it works
Anonim

The quantum world often contradicts common sense. Nobel laureate Richard Feynman once said: "I think I can safely say that no one understands quantum mechanics." Quantum teleportation is just one of those strange and seemingly illogical phenomena.

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In 2017, researchers from China teleported the object into outer space. It was not a man, not a dog, or even a molecule. It was a photon. Or rather, information describing a specific photon. But why is this called teleportation?

The bottom line is that quantum teleportation has little to do with teleportation itself. It is rather a matter of creating an internet that cannot be hacked. But before we go directly to this issue, let's talk about a paradox.

The brilliant physicist and author of Special and General Theories of Relativity, Albert Einstein, considered quantum mechanics to be an erroneous theory. In 1935, together with physicists Boris Podolsky and Nathan Rosen, he wrote an article in which he defined a paradox that casts doubt on almost everything related to quantum mechanics - the EPR paradox.

Quantum mechanics is the science of the smallest aspects of the universe: atoms, electrons, quarks, photons, and so on. It reveals paradoxical and sometimes contradictory aspects of physical reality. One of these aspects is the fact that by measuring a particle, you "change" it. This phenomenon was eventually called the observer effect: the act of measuring a phenomenon irreparably affects it.

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Often, in order to observe an atom, we shine on it. The photons of this light interact with the particle, thereby affecting its position, angular momentum, spin, or other characteristics. In the quantum world, using photons to observe an atom is akin to using bowling balls to count the pins at the end of a bowling alley. As a result, it is impossible to know exactly all the properties of a particle, since in the process of studying it, the observer influences the result.

The observer effect is often confused with the idea that consciousness can somehow influence or even create reality. In fact, there is nothing supernatural about this effect, since it does not require consciousness at all.

Photons colliding with an atom produce the same observer effect, regardless of whether they are moving towards it due to actions from the side of human consciousness or not. In this case, "to observe" is simply to interact.

We cannot be outside observers. In quantum systems, a person always takes an active part, blurring the results.

This was exactly what Albert Einstein did not like. For him, this inherent ambiguity indicated an incompleteness in quantum mechanics that needed to be eliminated. The scientist believed that reality could not be so unreliable. This is exactly what his famous phrase refers to: "God does not play dice with the Universe."

And nothing has emphasized the weakness of quantum mechanics more than the paradox of quantum entanglement.

Sometimes, on a quantum scale, particles can become interconnected in such a way that measuring the properties of one particle instantly affects another, no matter how far apart they are. This is quantum entanglement.

According to Einstein's theory of relativity, nothing can travel faster than light. However, quantum entanglement seemed to break this rule.If one particle is entangled with another, and any possible change that occurs with one of them affects the second, then there must be some kind of connection between them. How else can they influence each other? But if this happens instantly, despite the distances, this connection must occur faster than the speed of light - hence the very EPR paradox.

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Einstein called this phenomenon "spooky action at a distance." The whole field of quantum mechanics seemed to him as flimsy as supposed quantum entanglement. Until the end of his life, the physicist tried unsuccessfully to "patch up" the theory, but nothing came of it. There was simply nothing to fix.

After Einstein's death, it was repeatedly proven that quantum mechanics is correct and works, even if it often contradicts common sense. Scientists have confirmed that the quantum entanglement paradox is a real phenomenon, and in general it is not a paradox. Despite the fact that entanglement occurs instantly, no information can be transferred between particles faster than the speed of light.

How does this all relate to quantum teleportation? Let's get back to our topic. The fact is that information can still be transmitted in this way. This is exactly what researchers from China did in 2017. Although it is called "teleportation", in fact, scientists have carried out the transfer of information between two entangled photons.

When a laser beam is directed through a special crystal, the photons emitted by it are entangled. So when one photon is measured in an entangled pair, the state of the other is immediately known. If you use their quantum states as a signal carrier, then information can be transferred between two photons. This has been done before in laboratories around the world, but never before has this process taken place at such a distance.

Chinese researchers have sent an entangled photon to a satellite 1,400 kilometers above Earth. They then entangled the photon that remained on the planet with the third photon, which made it possible to send its quantum state to the photon on the satellite, thereby effectively copying the third photon in orbit. However, the third photon was not physically transferred to the satellite. Only information about its quantum state was transmitted and restored.

So it wasn't Star Trek teleportation. But the biggest breakthrough in this experiment was not teleportation, but communication.

A quantum Internet based on entangled particles would be nearly impossible to hack. And all thanks to the effect of the observer.

If someone tries to intercept one of these quantum transmissions, in essence, it will be an attempt to observe the particle, which - as we already know - will change it. The compromised transmission would be immediately visible, as the particles would cease to be entangled or the transmission would be completely destroyed.

The Quantum Internet would be a nearly 100% secure communications network. Without access to entangled particles, no one could hack it. And if someone did gain access to one of the entangled particles, they would immediately notice it, since the particle would disappear, which means that the Internet would stop working. This is how it can be more useful than a device for teleporting photons.

Researchers had to make over a million attempts to successfully entangle just over 900 particles. Since photons must pass through our atmosphere, there is a high likelihood that they will interact with other particles, therefore, will be "observed", eliminating entanglement and completing the transmission.

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Will we one day - sometime in the distant future - use this same technique to teleport large objects or even people? In theory, yes. This would entangle every particle in the body with the same number of particles at the destination. Each state and position of all your particles will need to be scanned and transferred to another location.The awaiting particles will become entangled and accept the information passed to them, instantly assuming a state identical to the original particles. This is essentially the same thing that happened to photons in the Chinese experiment. The only difference is that here we are talking about every particle in your body.

However, you shouldn't be overjoyed. Teleportation is also subject to the observer effect. A scanning process that measures all of your particles would instantly change all of them. It is possible that the changes were unpleasant for you, you would turn into an unrecognizable quantum slime. You would cease to exist at the initial point and appear at another - exactly the same, but with a new set of particles. But whether you remain yourself or not is a completely different question.

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