Contrary to the laws of classical mechanics, we have learned to transmit information faster than the speed of light. RIA Novosti found out how qubits exchange data and why it is impossible to teleport a material object.
Mysterious quantum world
In the quantum world, information is measured in qubits. Unlike classical bits, they are capable of staying simultaneously in two states - logical zero and one - until they are measured, or rather, information is read.
The role of a qubit is played by an artificial atom with two energy levels. If the atom is at the lower energy level, the state of the system is logical zero, at the upper one is logical one. Physically, a qubit can be embodied in a photon, molecule, ion, atom, quantum dot - in everything that emits and absorbs quanta of electromagnetic energy. For example, superconducting qubits are an electrical circuit made of thin layers of metal cooled to ultra-low temperatures, between which pairs of electrons tunnel through thin layers of insulator.
Since we are talking about the quantum world, it is impossible to say in what state the electron in the qubit is at each moment of time. This opens up opportunities for teleportation - the transmission of something in space.
“Quantum teleportation requires three superpositioned qubits. Let's say we need to transfer information from the first element to the third, and they should not interact, that is, they should not be close. Then the third and second qubits are entangled using a logical operation - their states become interdependent, and they themselves are called entangled. And if the state of one of them is measured, then the state of the second will automatically be opposite. It's like throwing black and white balls into a box, and then pulling out one of them at random: the color of the second will be known with 100% probability, says Ilya Besedin, an engineer at the Superconducting Metamaterials Laboratory at NUST MISIS.
Then the second qubit must interact with the first. There are two main ways to get them to “chat”. First, the resonant frequency of one atom is changed so that it coincides with the frequency of another, after which the excitation from one goes to another through the electric field. The second option is that the system is exposed to microwave radiation so that the absorption coefficient of one atom depends on the state of another. After the qubits have "talked", their states are read.
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In fact, at this moment, the qubits turn into classical bits with known information. Then a logical operation is performed on the third qubit, and it turns out to be in the state of the first. Recall that the first and third qubits have never interacted, except for indirect "communication" through the second qubit. In addition, the third was in contact with the second before he exchanged information with the first.
Confused? Then imagine that you got an A for the exam and shared your joy with your dad. Then they went to my mother and told her the same thing. And she told you that she scratched the car. And after your conversation, dad in an unknown way learns about this trouble. It is difficult to understand quantum mechanics - it is better to just come to terms with its laws.
You can't argue with the theory of relativity
With the help of quantum teleportation, information can be transmitted over long distances. The record so far belongs to Chinese scientists, who sent data from Earth to a satellite over 1400 kilometers. Moreover, the qubits themselves exchange data instantly, even faster than the speed of light.
Scientists have confirmed this by simultaneously measuring the state of two entangled qubits at different locations. It turned out that they really "feel" each other's changes faster than light moves.
To extract information from a qubit, it must be decoded using classical bits, the transmission rate of which cannot exceed the speed of light. Thus, although the quantum world provides incredible opportunities, people, due to their classical nature, sometimes simply cannot take full advantage of them.
“But quantum teleportation is perfect for encrypted data transmission. Of course, information can also be encrypted using classical algorithms. But this method has a weakness: key exchange. With sufficient computing power, the intercepted encryption can always be read,”says the expert.
And protocols based on quantum teleportation allow you to mathematically prove that the quantum line is not being tapped. As soon as an outsider connects to it, the quality of the transfer of the quantum state deteriorates significantly, regardless of the technical equipment of the intruder. And both parties immediately discover that their conversation is no longer private.
Will there be no teleport?
To share a funny video with a friend, you both need computers or smartphones. The same is with the teleportation of data between qubits: in order to transfer the state, you need a transmitter qubit and a receiver qubit, which are already located in the right place. That is, before sending data, you need to physically move the object that will receive it. And so far we can do this only in a classical way: along a well-known trajectory - from point "A" to point "B". And by no means instantaneously.
And what about the teleportation of any material object as a whole - for example, a person? After all, in the final analysis, matter consists of atoms, that is, quantum systems between which information can be transmitted. To do this, you will have to teleport data about all the atoms of the body to other atoms located in another place, and thereby recreate a person.
But for each act of transfer, complex technical equipment is required. A person weighing about 70 kilograms contains 6.7 * 1027 atoms. It is incredibly difficult to transmit information about all particles with 100% accuracy - and at the moment it is not technically feasible. Still, teleportation of a material object is too attractive a task to refuse.