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posted by martyb on Thursday July 30 2020, @07:42AM   Printer-friendly
from the ♫-we're-going-back-in-time-♫ dept.

Simulating quantum 'time travel' disproves butterfly effect in quantum realm:

Using a quantum computer to simulate time travel, researchers have demonstrated that, in the quantum realm, there is no "butterfly effect." In the research, information—qubits, or quantum bits—'time travel' into the simulated past. One of them is then strongly damaged, like stepping on a butterfly, metaphorically speaking. Surprisingly, when all qubits return to the 'present,' they appear largely unaltered, as if reality is self-healing.

[...] In the team's experiment, Alice, a favorite stand-in agent used for quantum thought experiments, prepares one of her qubits in the present time and runs it backwards through the quantum computer. In the deep past, an intruder—Bob, another favorite stand-in—meaures[sic] Alice's qubit. This action disturbs the qubit and destroys all its quantum correlations with the rest of the world. Next, the system is run forward to the present time.

According to Ray Bradbury, Bob's small damage to the state and all those correlations in the past should be quickly magnified during the complex forward-in-time evolution. Hence, Alice should be unable to recover her information at the end.

But that's not what happened. Yan and Sinitsyn found that most of the presently local information was hidden in the deep past in the form of essentially quantum correlations that could not be damaged by minor tampering. They showed that the information returns to Alice's qubit without much damage despite Bob's interference. Counterintuitively, for deeper travels to the past and for bigger "worlds," Alice's final information returns to her even less damaged.

"We found that the notion of chaos in classical physics and in quantum mechanics must be understood differently," Sinitsyn said.

The more damage you do in the past, the less the present is affected?


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  • (Score: 4, Insightful) by anubi on Thursday July 30 2020, @09:31AM (1 child)

    by anubi (2828) on Thursday July 30 2020, @09:31AM (#1028538) Journal

    I use device models all the time with computer analysis. Using models, I can build devices with phenomenal performance.

    However I usually can't build a physical device that has that kind of performance. My model is simply a model. Not exact. I learned long time ago that one should always verify that something really works by building one and verifying it does what it's supposed to do.

    --
    "Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
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  • (Score: 2) by sjames on Friday July 31 2020, @01:36PM

    by sjames (2882) on Friday July 31 2020, @01:36PM (#1029270) Journal

    This. Models and simulations are all implemented based on theory. They cannot show anything that theory doesn't predict.

    They can be useful in cases where we don't fully understand the implications of a theory, and they can be compared to a physical experiment to see how well our theory does against reality.

    Notably, what they did here was not actually sending the qbit back in time. If it was, the story would be

    Alice gets ready to create a qbit and exclaims "OH! I seem to have already done it, that's odd"