Around us, everything is constantly changing. Our daily lives are full of changes, and we know from experience that many of them are impossible to reverse. Indeed, all the processes that surround us seem to follow a single, well-defined direction in time: the glass falls to the floor and shatters, but we will not see its fragments form and return again to the table from which they fell.
However, the kingdom Quantum mechanics It is not subject to the same rules, and it can even be said that the direction of time is not suitable for naturally occurring processes. That is, the same “forwarders” can take place as the “successors”.
Two years ago, a team of Russian scientists managed to simulate the reversal of time on a computer, creating a situation in which the “arrow of time” goes backwards. Now, a team of researchers led by physicists from the University of Vienna has managed to go one step further, and turn that simulation into reality by showing that, at least in certain quantum systems, The time direction of operations can be reversed.
Specifically, the physicists were able to return the photon to the temporary state before the experiment. In an analogy with the microscopic world, they return the glass, as it were, to the table from which it fell. The work is a demonstration of the call “rewind protocol” It has just been published in the magazine ‘optics’.
Most of the changes that surround us in our daily lives are impossible to reverse. Broken glass will never be put back together again, and an egg will never go back into its shell after being fried. However, it is theoretically possible to reverse the seemingly irreversible. It suffices for this to know precisely the location, speed and direction of every atom in the cup (or the egg) at every moment. Something impossible in practice.
A separate world
In the world of subatomic particles, the problem becomes more complex, because one of the basic tenets of quantum physics is that simply observing a system causes it to change. This makes it impossible, even in principle, to track how the system has changed over time and to reverse the process. However, the laws of quantum mechanics also open up new possibilities, such as so-called “universal rewind protocols,” which allow changes in a quantum system to be reversed without having to know exactly what they are. That is, without having to monitor them.
Led by Philip Walther, the physics team has successfully implemented a global rewind protocol. By combining a new theoretical protocol with a complex optical setup, the group has shown that it is indeed possible to reverse changes in a quantum system, such as a photon. To do this, they used ultrafast fiber-optic components and free-space interferometers arranged like a quantum switch.
In this way, they were able to successfully reflect the temporal evolution of a single photon without knowing how it changed over time, or even its initial and final states. “Surprisingly, this protocol does not even require knowledge of the nature of interactions with the quantum system,” says Peter Schiansky, first author of the article.
According to the researchers, their global rewind protocol can be modified to succeed with a very high probability. Evidence that rewind protocols exist in this general form, and are also technically feasible, contributes to our understanding of fundamental quantum mechanics. In the future, it can become a useful tool for information technologies. quantitative information.
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