How scientists have traced time (with a quantum computer)

For a split second, they realized something that seemed impossible.

Researchers from the Institute of Physics and Technology of Moscow, MIPT for its acronym, as well as scientists in the United States and Switzerland have managed to get a quantum computer to return to the state that does not counted only a fraction of a second in the past.

In other words, they managed to recover time in this quantum domain.

The experiment seems to contradict a fundamental law of physics, the second law of thermodynamics.

"This law is closely related to the notion of time as an arrow that only goes in the past, from the past to the future," said Gordey Lesovik, researcher at MIPT and lead author of the study published in the journal Scientific Reports.

"We have artificially created a state that is moving in a direction opposite to that of the thermodynamic time arrow," he added.

Why do not we see an eruption upside down?

What is the difference between the future of the past?

Most laws of physics do not distinguish between the future and the past.

The researchers point out that we can understand this, considering an equation that describes the collision and rebound of two billiard balls.

If we recorded the shock with a camera and then saw the band in the opposite direction, the movement in both directions could be represented by the same equation.

However, if we imagine a recording in which we see the balls disperse in all directions when it is hit by a billiard stick and we see the film backwards, what we will see will seem little likely.

And this is due to our intuitive understanding of the second law of thermodynamics, which states that an isolated system remains static or evolves to a more chaotic state, but never in a more orderly state.

Most of the other laws of physics do not prevent the balls from sitting alone in a triangle, nor that the tea diffused in an infusion can flow back into the tea bag, or that the lava returns on a volcano in a rash invert, emphasize the scientists.

We do not see anything of this happening in the world around us because it would require an isolated system to badume a higher order state without any intervention, which goes against the second law of thermodynamics, a law "whose intimate nature this has not yet been explained in detail."

Quantum bits

If we do not see the weather return to the observable world, how did scientists make this possible?

The "time machine" used by researchers is a quantum computer.

In clbadical digital computing, a bit or an information unit can only take two values: 0 or 1.

On the contrary, in quantum computing, we use cubes or quantum bits, which use the incredible properties of subatomic particles.

For example, electrons or photons can exhibit two states at once, a phenomenon called superposition. Therefore, a cube can be 0, 1 or 0 and 1 at a time.

As a result, a computer based on cubits can perform many more calculations at a speed higher than that of a conventional machine.

"A kick at a pool table"

Lesovik and his colleagues designed an ingenious experiment.

They used a program that converts the initial state of the cubits into an IBM quantum computer into a changing and increasingly complex pattern of zeros and ones.

In this process, the order is lost, in the same way that the billiard balls formed into a triangle disperse when they are hit by another ball driven by a billiard stick.

Another program then changed the state of the quantum computer so that it evolves upside down, from chaos to order.

In other words, the state of the cubits returned to its original position.

The experience is tantamount to "kicking a pool table so the balls rearrange themselves in their triangle formation," according to the researchers.

Applications

Scientists have discovered that the quantum computer of two cubits had regained its initial state in 85% of cases. But when three cubits were used, the error rate was 50%.

This is due to imperfections in the design of quantum computers that could be overcome in the future, according to scientists.

The experience is far from suggesting that we can travel back in time in the future.

But this could have practical applications.

"Our algorithm could be updated and used to test and eliminate errors in programs written for quantum computers," said Lesovik.

Scientists could verify that the software of a quantum computer is working properly by making it go back in time.

And any progress in the development of quantum computing, the "holy grail" of computing, could have consequences for all.

Computer scientists say that quantum computers could accelerate the discovery of new drugs, decipher the most complex cryptographic security systems, help design new materials, and more accurately model climate change.