Quantum algorithm reverses qubits
14 Mar 2019 by hhwdjwbphm.d hhwdjwbphm.d
Russian physicists say they have returned the state of a quantum computer to a fraction of a second in the past.
Moscow Institute of Physics and Technology scientists used the public IBM quantum computer to observe two qubits as they entered a state of disorder. Using a program akin to a microwave background fluctuation in the case of an electron, they returned the qubits to their original state.
Gordey Lesovik at MIPT said: “We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time.
“This is one in a series of papers on the possibility of violating the second law of thermodynamics. That law is closely related to the notion of the arrow of time that posits the one-way direction of time: from past to the future.”
Using snooker as a loose analogy, a cue bill hitting a pyramid of balls is a demonstration of the second rule of thermodynamics – that an isolated system either remains static or evolves toward a state of chaos. MIPT claims to have reversed this rule within the quantum computer demonstrator.
They found that in 85% of cases, the two-qubit quantum computer had returned to the initial state. When there were three qubits, more errors were seen. But as more sophisticated quantum devices are designed, the error rate is expected to drop.
The time-reversal algorithm could be used to make quantum computers more precise by reducing noise and errors, according to the researchers.
“While in nature the complex conjugation needed for time reversal may appear exponentially improbable, one can design a quantum algorithm that includes complex conjugation and thus reverses a given quantum state,” their paper, published in Scientific Reports, says.
How much potential does this have to reverse time à la the Tardis? From their research findings, the scientists calculated the probability that an electron in empty interstellar space will spontaneously travel back to its recent past.
They concluded that if you spent 13.7 billion years observing 10 billion freshly localised electrons every second, this reverse evolution would occur only once, and it would travel no more than one ten-billionth of a second into the past.
