# Physicists Reverse Time Using Quantum Computer

fahrbot-bot shares a report from Phys.Org: Researchers from the

Moscow Institute of Physics and Technology teamed up with

colleagues from the U.S. and Switzerland and returned the state of

a quantum computer a fraction of a second into the past. They also

calculated the probability that an electron in empty interstellar

space will spontaneously travel back into its recent past. The

study is published in Scientific Reports. Quantum physicists from

MIPT decided to check if time could spontaneously reverse itself at

least for an individual particle and for a tiny fraction of a

second. That is, instead of colliding billiard balls, they examined

a solitary electron in empty interstellar space. “Suppose the

electron is localized when we begin observing it. This means that

we’re pretty sure about its position in space. The laws of quantum

mechanics prevent us from knowing it with absolute precision, but

we can outline a small region where the electron is localized,”

says study co-author Andrey Lebedev from MIPT and ETH Zurich. The

physicist explains that the evolution of the electron state is

governed by Schrodinger’s equation. Although it makes no

distinction between the future and the past, the region of space

containing the electron will spread out very quickly. That is, the

system tends to become more chaotic. The uncertainty of the

electron’s position is growing. This is analogous to the increasing

disorder in a large-scale system — such as a billiard table — due

to the second law of thermodynamics. “However, Schrodinger’s

equation is reversible,” adds Valerii Vinokur, a co-author of the

paper, from the Argonne National Laboratory, U.S. “Mathematically,

it means that under a certain transformation called complex

conjugation, the equation will describe a ‘smeared’ electron

localizing back into a small region of space over the same time

period.” Although this phenomenon is not observed in nature, it

could theoretically happen due to a random fluctuation in the

cosmic microwave background permeating the universe. The team set

out to calculate the probability to observe an electron “smeared

out” over a fraction of a second spontaneously localizing into its

recent past. It turned out that even across the entire lifetime of

the universe — 13.7 billion years — observing 10 billion freshly

localized electrons every second, the reverse evolution of the

particle’s state would only happen once. And even then, the

electron would travel no more than a mere one ten-billionth of a

second into the past. The researchers then attempted to reverse

time in a four-stage experiment by observing the state of a quantum

computer made of superconducting qubits, instead of an electron.

The researchers “found that in 85 percent of the cases, the

two-qubit quantum computer returned back into the initial state,”

reports Phys.Org. “When three qubits were involved, more errors

happened, resulting in a roughly 50 percent success rate. According

to the authors, these errors are due to imperfections in the actual

quantum computer. As more sophisticated devices are designed, the

error rate is expected to drop.”

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Source: *FS – All – Science News 2 Net

Physicists Reverse Time Using Quantum Computer