The state of a quantum computer was sent back in time by physicists from the Moscow Institute of Physics and Technology and their American and Swiss counterparts by a fraction of a second. They also determined the odds of an electron in empty interstellar space making a spontaneous trip into the past. Scientific Reports is where you may read the whole thing.
This is the first of a series of studies exploring the potential for breaking the second rule of thermodynamics. “That law is closely related to the notion of the arrow of time that posits the one-way direction of time from the past to the future,” said research lead author and MIPT Laboratory head Gordey Lesovik.
We started out by explaining a second-kind “local perpetual motion machine.” Lesovik continued, “Then in December, we released an article discussing the violation of the second rule via a gadget called Maxwell’s demon. “We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time,” the authors of the most recent publication on the subject write.
What makes the future different from the past
The majority of physical rules do not differentiate between the present and the past. Take the case of two identical billiard balls colliding and rebounding, which may be described by an equation. The same equation can be used to describe a close-up camera recording of the incident played backward. In addition, it is impossible to tell if the recording has been altered. Both interpretations seem reasonable. The pool balls appear to defy common perceptions of time.
But picture capturing the moment the cue ball shatters the pyramid and the billiard balls fly in every direction. In that circumstance, the real-world scenario can be easily distinguished from the reverse playback. The intuitive interpretation of the second law of thermodynamics, which states that an isolated system either stays static or progresses towards a state of chaos rather than order, makes the latter seem ludicrous.
In general, the rules of physics don’t preclude something like a volcano “erupting” in reverse or a pyramid of rolling billiard balls assembling. However, these events are never witnessed because they contradict the second law of thermodynamics by necessitating the spontaneous orderly development of a closed system in the absence of any external influence. Although this law’s exact nature remains a mystery, scientists have made significant progress in deducing its fundamental principles.
Spontaneous time reversal
MIPT’s quantum physicists wanted to see if, at the level of a single particle and a trillionth of a second, time might spontaneously reverse itself. That is, instead of studying the results of a pool ball collision, scientists looked at a single electron floating in the void of space.
Let’s say we start our observations with the electron in a localized state. As a result, we can confidently say where in space it is. Co-author Andrey Lebedev from Michigan Technological University and the Swiss Federal Institute of Technology adds, “We can outline a small region where the electron is localized, but we can’t know it with absolute precision because of quantum mechanical laws.”
The evolution of the electron state is described by Schrödinger’s equation, the scientist says. Even though it doesn’t care about the future or the past, the area of space that contains the electron will expand very rapidly. In other words, the system evolves towards more anarchy. The position of an electron is becoming increasingly ambiguous. This is similar to how the second law of thermodynamics causes increasing disorder in a large-scale system, like a billiard table.
However, Schrödinger’s equation may be solved backward, as noted by the paper’s coauthor, Valerii Vinokur of the Argonne National Laboratory in the United States. As the author puts it, “mathematically, it means that under a certain transformation called complex conjugation, the equation will describe smeared electron localizing back into a small region of space over the same time period.” Although this has never been seen in the wild, it is possible that it results from random fluctuations in the pervasive cosmic microwave background.
The group’s first goal was to determine the likelihood of stumbling across spontaneous localization into the recent past of an electron that had been “smeared out” over a fraction of a second. The observation of 10 billion newly localized electrons every second throughout the course of the 13.7 billion years of the universe’s existence revealed that the reversal of the particle’s status will occur just once. The farthest back in time an electron could go is one ten-billionth of a second.
Massive events, such as those involving billiard balls or volcanoes, take place over considerably longer periods of time and include an incredible amount of electrons and other particles. That’s why we never see an ink blot lift off the page or an aged person miraculously rejuvenate.
Reversing time on demand
In a subsequent four-part experiment, the scientists tried to undo time. Superconducting qubits, which are made up of two and later three basic components, were used to observe the state of a quantum computer.
One, place an order. Zero, or the ground state, is the default for each qubit at startup. This neat arrangement is analogous to a localised electron or a rack of billiard balls just before the break.
The second phase is decay. Somehow, the order went missing. The state of the qubits resembles the smearing of an electron over a larger area of space or the rack being broken on a pool table in that it gradually evolves into a more complex pattern of zeros and ones. To accomplish this, the quantum computer’s evolution programme is temporarily activated. It’s true that natural wear and tear from interacting with the environment would lead to a comparable decline. However, the experiment’s final phase will be made possible through a well-crafted autonomous evolution programme.
Third, time is reversed. To force the quantum computer to evolve “backwards,” or from disorder to predictability, a specialised programme alters the system’s state. This process is analogous to the fluctuations in the electron’s random microwave background, but here they are intentionally created. In the example of the billiard, a flawless kick to the table would be a ridiculously over-the-top simile.
Restoration occurs in Stage 4. The second-stage evolution programme has been restarted. If the “kick” is successfully delivered, the programme does not create more disorder but rather rewinds the state of the qubits into the past, similar to how a dispersed electron would become localised or how billiard balls would retrace their trajectories in reverse playback, eventually forming a triangle.
After 85 per cent of trials, the two-qubit quantum computer reverted to its original state, as discovered by the researchers. More failures occurred with three qubits, leading to a success rate of about 50%. The authors argue that flaws in the implementation of quantum computing are to blame for these mistakes. The error rate is predicted to decrease as more complex gadgets are developed.
It’s interesting to think that the time-reversal algorithm itself might help improve the accuracy of quantum computers. “Our algorithm could be updated and used to test programmes written for quantum computers and eliminate noise and errors,” Lebedev said.