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Scientists ‘reverse time’ with quantum computer in breakthrough study

The Independent logo The Independent 3/14/2019 Andrew Griffin
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Scientists have reversed the direction of time with a quantum computer.

The breakthrough study seems to contradict basic laws of physics and could alter our understanding of the processes governing the universe.

In a development that also represents a major advance in our understanding of quantum computers, by using electrons and the strange world of quantum mechanics researchers were able to turn back time in an experiment that can be likened to causing a broken rack of pool balls to go back into place.

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Anyone watching the computer would see the event as if time had turned backwards.

The researchers – from the Moscow Institute of Physics and Technology (MIPT) and helped by colleagues in Switzerland and the US – expect the technique to improve, becoming more reliable and precise with time.

Lead researcher Dr Gordey Lesovik, who heads the Laboratory of the Physics of Quantum Information at the MIPT, said: “We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time.”

The “time machine” described in the journal Scientific Reports consists of a rudimentary quantum computer made up of electron “qubits”.

A qubit is a unit of information described by a “one”, a “zero”, or a mixed “superposition” of both states.

In the experiment, an “evolution program” was launched which caused the qubits to become an increasingly complex changing pattern of zeros and ones.

During this process, order was lost – just as it is when the pool balls are struck and scattered with a cue.

But then another program modified the state of the quantum computer in such a way that it evolved “backwards”, from chaos to order.

It meant the state of the qubits was rewound back to its original starting point.

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Most laws of physics work both ways, in the future and the past. If you see a video of a pool ball knocking into another one, for instance, and then reverse that same video, the physical processes would both make sense and it would be impossible at the level of physics to know which way around would be correct.

But the universe does have one rule that goes only in one way: the second law of thermodynamics, which describes the progression from order to disorder.

If you saw a video of someone breaking a perfectly arranged triangle of pool balls into a mess, for instance, then watching that backwards would obviously look nonsensical.

The new experiment is like giving the pool table such a perfectly calculated kick that the balls rolled back into an orderly pyramid.

The scientists found that, working with just two qubits, “time reversal” was achieved with a success rate of 85 per cent. When three qubits were involved more errors occurred, resulting in a 50 per cent success rate.

The error rate is expected to drop as scientists improve the sophistication of the devices used, the researchers behind the discovery said.

The experiment could have a practical application in the development of quantum computers, the scientists said.

“Our algorithm could be updated and used to test programs written for quantum computers and eliminate noise and errors,” said Dr Lesovik.

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