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Scientists appear to have "inverted time" in a two-bit and three-bit quantum computer after calculating the probability that the phenomenon will occur naturally in a localized electron.
Reverse the entropy of a two Qubits system
Scientists from Russia, Switzerland and the United States came together to apparently reverse the entropy of a two-qubit quantum computer with an accuracy of 85% and about 50% in a three-qubit system, although they notice that the remaining inaccuracy is due to imperfections in the quantum computer itself, not their algorithm.
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Entropy, defined as the measure of disorder in a system, naturally increases over time as nature goes from order to disorder. In the case of the quantum computer built by the researchers, the system that starts in a state where the qubits are initially 0, degrades over time into a random character of 1 and 0.
This is consistent with the Second Law of Thermodynamics (SLT), which states that in an isolated system, entropy never decreases. What the researchers have done is seemingly to rewind this entropy to return to the initial state of the quantum computer on demand, thus offering new opportunities for error correction in quantum computers, this which could greatly improve their deployment.
Spontaneous return in localized electrons
Researchers from the Moscow Institute of Physics and Technology (MIPT), the Eidgenössische Technische Hochschule Zurich (ETH Zürich) and the Argonne National Laboratory in the United States (ANL) – who published their results today in the journal Scientific reports-, began by calculating the probability that a localized electron returns to its previous state from one instant to another.
"Suppose the electron is localized when we start to observe it, that means we are pretty sure of its position in space.The laws of quantum mechanics prevent us from knowing it with a absolute accuracy, but we can define a small region where the electron is located, "said Andrey Lebedev, co-author of the study, MIPT and ETH Zurich.
The evolution of the state of the electron from one moment to the next is determined by the Schrödinger equation. This equation does not distinguish between times, but according to the SLT, the area in which the electron can appear increases rapidly.
"However, the Schrödinger equation is reversible," adds Valerii Vinokur, of ANL and a co-author of the article. "Mathematically, this means that under a certain transformation, called complex conjugation, the equation will describe a" spotted "electron locating itself in a small region of space during the same period."
Although this reversal was not observed naturally, scientists felt that it was theoretically possible.
The researchers compare this to a billiard ball hitting another. If you recorded the event normally, an equation would govern the behavior of the different positions and speeds of the pool balls, ie their state at any time.
However, if you reverse the recording, the same equation will also govern this state transition. Essentially, 2X is equal to Y, but Y is also equal to 2X, depending on how you want to read the equation. Both are valid and there is no way of saying which form was the "original" equation.
In the case of an electron, it was theoretically possible to reverse the Schrödinger equation, so that if the equation governing the state transition of the electron was Y = 2X, then Y could be obtained from 2X in the same way. equation, 2X = Y.
To determine the natural frequency of this phenomenon, the team calculated the probability that an electron "goes out" for a fraction of a second and spontaneously locates itself in an earlier state, a more precise way of going back in time. .
They calculated that if you looked at 10 billion newly located electrons over the life of the universe – 13.7 billion years – you would see this phenomenon only once. of one second in time.
Rewinding time on request
If the probability that a single electron evolves into a past state is virtually impossible, how then did these scientists recreate the effect in qubit quantum states with a 85% success rate in a system with two qubits and a little less than 50% for a three qubit system?
Using the analogy of the billiard ball, rather than two billiard balls, this seems more like using a rack of billiard balls, breaking them with a white ball and reassembling them into a pyramid .
The researchers basically designed an algorithm that they describe as giving the pool table a "kick" that reverses the changes in state in the qubits, making them return to their previous states. This would be tantamount to hitting the pool table in the exact spot, with the exact force needed to throw all the balls straight back, and eventually turn into a pyramid.
"Our algorithm could be updated and used to test programs written for quantum computers and eliminate noise and errors," explained Lebedev.
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