Connect the future to the past

Israeli scientists have created a quantum entanglement between a particle that no longer exists and a particle that has not yet been created

Quantum entanglement is one of the amazing phenomena in quantum mechanics. When two particles are entwined, there is such a close coordination between them that it will be maintained even if the particles are at a great distance from each other. In quantum mechanics, a particle can be in several states at the same time, until a measurement reveals what its "true" state is. In a pair of intertwined particles, a measurement of one particle will immediately affect the state of the other particle, even if the particle we measured is in Jerusalem, and the other is - for example - on the moon. This is why Albert Einstein opposed quantum mechanics at the time: apparently information is transferred between the interwoven particles faster than the speed of light, even though according to the special theory of relativity, nothing can move faster than light. In 1981, physicists proved, with the help of an experiment devised by the Northern Irish physicist John Bell, that Einstein was wrong in his opposition, and that quantum entanglement does exist. The researchers settled the paradox presented by Einstein (for now), by explaining that no information is transferred between the particles, therefore there is no violation of the theory of relativity.

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Since that initial proof, quantum entanglement has gradually become a household name in many laboratories around the world, and scientists are trying to harness it both for a better understanding of physical phenomena, and for harnessing these phenomena to develop physical tools that previously seemed imaginary, but in recent years they already seem closer to reality. One of them, for example, is teleportation - sending objects to an unlimited distance (such as the transfer of crew members from the spaceship "Enterprise" to it in the "Star Trek" series). Another idea is the quantum computer, whose basic unit is not binary like a normal computer (can only be in one of two states, 0 or 1), but quantum, and can be at any given time in both states at the same time, or in a long series of intermediate states. Such units will give even a relatively small computer tremendous computing power compared to the computers available to us today, and will bring about a real revolution in many areas of our lives.

distant even in time

Since Schroedinger came up with the idea of ​​quantum entanglement in the 30s, researchers have referred to the separation between the quantum particles as a spatial separation. As mentioned - they can even be at different ends of the universe, and will still remain intertwined. However, researchers from the Hebrew University have now proven that the separation can exist not only in distance, but also in time. That is, it is possible to interweave a particle that no longer exists, with a particle that has not yet been created, and thus it is possible - theoretically - to influence the state of the particle in the future, and even in the past. To do the experiment, the researchers used pairs of light particles (photons), as you can see in the diagram on the right. They first created one pair of entangled photons, let's call them 1 and 2. After photon no. 1 disappears, create another pair, 3 and 4. So a joint measurement is made for photons 2 and 3, and interweaved between them. Thus, in fact, entanglement is also formed between photons 1 and 4, although 4 is formed only after no. 1 no longer existed. The experiment was led by Dr. Hagai Eisenberg from the Department of Physics, with research student Eli Magidish, and with research students Assaf Halevi, Assaf Shachem and Liat Debrat. In an article recently published in the journal Physical Review Letters, the researchers created a separation of 200 billionths of a second (nanoseconds), between the two pairs of photons, and proved the entanglement between the photons that did not exist at the same time. According to them, this is proof of the feasibility that it is possible to create a longer separation as well.

past and future

A laboratory in Rome can intertwine a pair of particles, and send one of them to London and one to distant Australia. The work of Magidish, Eisenberg and their partners proves that the scientists in London will be able to make measurements with their particle, without having to wait for the other particle to reach its destination to make the measurements they are requesting - they will remain intertwined despite the time differences between them.
"Our work demonstrates an interweaving between two particles that did not get to know each other," says Magidish. "Scientifically, it illuminates the question of what time actually is. In this case the past can influence the future, and vice versa - mainly in the philosophical sense. However, the irrelevance of time in the development of the entire system has an effect on the more efficient planning of quantum computing and communication networks, which we expect in the future."