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It’s not time travel, but scientists can turn back clock on a quantum computer

When Cher sang about wanting to turn back time, she could have packed in the career as a pop star and taken up quantum computing research if she had really meant those words. That’s one possible takeaway from a newly published piece of research from the journal Scientific Reports. In the report, physicists reveal how they were able to wind the clock on a quantum computer a fraction of a second backward in time. Well, kind of.

Researchers from the United States, Russia, and Switzerland sent a quantum bit (called a qubit) from a more complicated state to an earlier, simpler one. The work was achieved using an IBM quantum computer.

“Here, we show that, while in nature the complex conjugation needed for time reversal is exponentially improbable, one can design a quantum algorithm that includes complex conjugation and thus reverses a given quantum state,” the researchers write in their paper’s abstract. “Using this algorithm on an IBM quantum computer enables us to experimentally demonstrate a backward time dynamics for an electron scattered on a two-level impurity.”

As MIT Technology Review magazine points out, this isn’t really reversing the course of time. It’s more like hitting rewind on a video and watching events play backward — only with the added cool factor that this was achieved using a quantum system. That doesn’t mean that it’s not potentially interesting research, though.

“On the fundamental level, we unraveled the quantum mechanical origin of the irreversibility of time,” Valerii Vinokour, a researcher at Argonne National Laboratory in Illinois, told Digital Trends. “The second law of thermodynamics tells us that a thermodynamic system cannot evolve backwards from the state with high entropy to the state with low entropy. Our novelty is in that we revealed that even the simplest pure quantum mechanical state evolves with the increasing complexity, so that even the simplest pure quantum state cannot reverse spontaneously its evolution.”

In addition to some highfalutin questions about cosmology and the universe, the work may also have more immediately applicable implications by helping eliminate noise and errors from programs written for quantum computers.

Sadly, one thing it apparently won’t do is take us closer to building an actual working time machine for transporting humans on Back to the Future-style jaunts. “Not really, no contribution to the time travel concept,” Vinokour said. “Time travel is a different and unrelated beast on which I would refrain from comments.”

Then again, isn’t that what someone would say if they had built a time machine? (Disclaimer: They really haven’t built one.)

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Luke Dormehl
I'm a UK-based tech writer covering Cool Tech at Digital Trends. I've also written for Fast Company, Wired, the Guardian…
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