Researchers send qubit back in time


Experiment reveals the possibility that an electron in space might ‘spontaneously localise into its recent past’. Samantha Page reports.


Time travel has long been a trope of science fiction, but the reality is rather different.

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Russian scientists have succeeded in reversing time, albeit on a very, very tiny scale.

The researchers, from the Moscow Institute of Physics and Technology, along with U.S. and Swiss colleagues, announce their findings in the journal Scientific Reports.

“We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time," says the study's lead author, Gordey Lesovik.

“This is one in a series of papers on the possibility of violating the Second Law of Thermodynamics. That law is closely related to the notion of the arrow of time that posits the one-way direction of time: from the past to the future.”

The Second Law of Thermodynamics affirms that any isolated system will degenerate into a more chaotic state.

In the experiment, Lesovik and colleagues observed two or three superconducting qubits in a quantum computer. Qubits are similar to standard computer bits, but rather than existing as either one or zero, they can exist in any superposition of those values.

The researchers liken the qubits to billiard balls that start out in a racked formation before the break. The qubits begin at zero and become increasingly more complex as time moves forward, just as billiard balls spread out across the table.

But in this experiment, the scientists use a special program to then kick-start backward evolution of the quantum state.

With two qubits, the results showed that 85% of the time they returned to their initial state – as though the billiard balls had spontaneously reracked themselves. With three qubits, the return rate was 50%. The researchers attribute the less-than-perfect outcomes to imperfections in the computer itself.

“Our findings break ground for investigations of the time reversal and the backward time flow in real quantum systems,” they write.

In the same paper, Lesovik and colleagues also calculate the probability that an electron in interstellar space would “spontaneously localise into its recent past”. In other words, they tried to find out if the time-traveling qubits would occur in the real world.

They found the odds of this happening to be pretty small: “If one spent the entire lifetime of the universe – 13.7 billion years – observing 10 billion freshly localised electrons every second, the reverse evolution of the particle's state would only happen once,” they write.“And even then, the electron would travel no more than a mere one ten-billionth of a second into the past.”

  1. http://dx.doi.org/10.1038/s41598-019-40765-6
  2. https://www.wired.co.uk/article/quantum-computing-explained
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