In the physical world, time marches in one direction, but things aren’t so straight forward in the quantum realm.
Researchers have discovered that it’s possible to speed up, slow down, or reverse the flow of time in a quantum system.
In the subatomic universe of quantum physics, you can achieve things considered impossible in our flesh-and-blood physical world. Things like superposition, entanglement, and even teleportation all seem possible when things go quantum. Now, scientists from the Austrian Academy of Sciences (ÖAW) and University of Vienna are adding a kind of time travel to the list.
In a series of papers published throughout the past few years on preprint servers and in various online journals (including Optica, arXiv, and Quantum), researchers including ÖAW’s Miguel Navascués and University of Vienna’s Philip Walther explain the possibility of speeding up, slowing down, and even reversing the flow of time within a quantum system.
Navascués compares the phenomenon to different movie-watching experiences. “In a theater [classical physics], a movie is projected from beginning to end, regardless of what the audience wants,” he explains to the Spanish-language newspaper scientists-prove-particles-in-a-quantum-system-can-be-rejuvenated.html” data-ylk=”slk:El País” class=”link “>El País. “But at home [the quantum world], we have a remote control to manipulate the movie. We can rewind to a previous scene or skip several scenes ahead.”
The researchers achieved this by “evolving” a single photon as it passes through a crystal. Using an experimental device called a “quantum switch,” the single photon of light returns to its previous state before it ever makes the journey. In a way, this is less Doc Brown-style time travel and more about reverting or otherwise altering the states of quantum particles, or “time translation” as Navascués described in 2020.
However, this isn’t exactly like a rewind button on your TV because usually, viewers can see how things got from plot point A to B—just sped up and in reverse. In quantum mechanics, however, simply observing a system causes it to change, which makes it impossible to track a system’s progress through time. Crucially, these rewinding protocols still work because they can be performed without knowing what the changes were or its “internal dynamics,” according to the scientists.
And this quantum time machine doesn’t just go one direction—Navascués says they’ve also hit upon a method for going forward in evolutionary time as well. He tells El País:
“To make a system age 10 years in one year, you must get the other nine years from somewhere. In a year-long experiment with 10 systems, you can steal one year from each of the first nine systems and give them all to the tenth. At the end of the year, the tenth system will have aged 10 years; the other nine will remain the same as when the experiment began.”
Sadly, these sci-fi findings in the quantum world can’t be sized up to send humans backward and forward in time, because a single human represents a mind-boggling amount of information to “rejuvenate”—in fact, the scientists estimate it would take millions of years to pull it off for just one second.
But for the teams at ÖAW and the University of Vienna, the point isn’t jetting off to the distant future of 2015, but the ability to increase the capability of quantum processors by arming them with the possibility of reversing errors in a system. After all, if life had a rewind button, wouldn’t you use it?
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