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