Consider this scenario: you’re in your 40s and you want to appear as you did 20 years ago when going on a date. While this may be unattainable in the conventional physical world, it is not out of the question in the quantum realm, where the fundamental building blocks of all reality are subatomic particles.

A group of researchers from the Institute of Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences (ÖAW), including Miguel Navascués and David Trillo from Spain, collaborated with Philip Walther and the experimental physics group of the University of Vienna on several research projects.

The team’s theoretical studies and experimental results demonstrating the feasibility of accelerating, decelerating and reversing the flow of time inside arbitrary, “even uncontrolled quantum systems” were published in in Physical Review X, Quantum, Arxiv, Physical Review Letters and Optica.

These extraordinary physical processes, which are able to alter the flow of time, are general: they have the same impact on all particles regardless of their make-up or interactions with other systems.

The basic physics rules we learn in school govern how everything we experience. But, scientists studying quantum physics concur that they cannot fully understand the subatomic universe, which forms all of reality at the tiniest scales.

There are examples of superposition (where a particle may be in one state, another, or both at once), entanglement (when action on one particle instantly affects the other, even if they are far apart), pseudo-telepathy, and teleportation in this unseen cosmos.

Now, thanks to the efforts of this group of researchers, it has been shown that these quantum particles may be rejuvenated or returned to a prior condition. Miguel Navascués uses a comparison to explain what the finding means and how it was proven.

The analogy of a movie theater versus home entertainment was used to illustrate the difference between classical physics and the quantum world. In classical physics, events progress from beginning to end like a movie projected in a theater, while in the quantum world, events can be manipulated like a movie watched at home with a remote control. The research team at ÖAW developed a “rewind protocol” that allows particles such as electrons, protons, or muons to revert to a previous state. This was demonstrated theoretically and experimentally by Trillo, who used a photon passing through a crystal to show this capability.

Using a “quantum switch” in a creative way lets the light particle go back to the way it was at the beginning of its journey.

For Walther, this was “one of the most difficult experiments” they’ve “ever built for a single photon.

“The fascinating thing is that [the particles] can return to a state you know nothing about.”

They explained that the experiment can be conducted without any prior knowledge of the system, including its internal dynamics and the interaction between the system and the experimenter. Navascués noted that the experiment is rooted in a century-old application of Einstein’s theory of relativity.

As explained by the authors: If one twin travels at high speed into space while the other remains on Earth, the traveling twin will return having aged less than their Earthbound counterpart. This is an example of time dilation, where time appears to pass slower for objects traveling at high speeds. The traveling twin could argue that their journey took less time than the time measured by the Earth-bound twin.

This relativistic event can be seen, but it is difficult to see since doing so requires a lot of energy or being close to a black hole. However, it is restricted in that it can only slow time; it cannot reverse or accelerate it.

Nevertheless, the team aimed to show that these limits “disappear when one leaves the realm of classical relativistic physics and enters the realm of non-relativistic quantum mechanics.”

They say that’s what they did. “We present a universal mechanism that, when it acts on any qubit, propagates it to the state it was in before the experiment began.” 

The novel mechanism is always effective, even when the experimental device is fully “invisible” to the qubit, unlike the group’s previously identified protocols, which only function with a specific probability threshold.

“We answered the question of whether such processes are allowed by the laws of quantum mechanics,” they added.

Can the knowledge be applied to bigger systems? The experiment was completed successfully using particles capable of storing one bit of information. While it is technically feasible to recreate the experience with a person, doing so would be worthless and impractical.

Theoretically, according to the authors, it would be possible to rejuvenate a person by placing them in a box with no external influences. However, the current protocols available make the likelihood of success very low. The amount of time required to complete the process is also dependent on the amount of information the system can store. Since a human being contains an enormous amount of information, rejuvenating a person for even a fraction of a second would take millions of years, making it an impractical approach.

The discovery isn’t a way to go back in time. Time moves on anyway, and the only thing that changes is our bodily condition.

The length of time necessary to finish the procedure, according to Navascués, is five minutes for a particle with the capacity to store one bit of information.

Fast-forwarding a particle to a different condition in the future is the same idea as aging it. It will take 10 years for a system to mature, according to Navascués. 

“You can’t create time out of nothing. To make a system age 10 years in one year, you must get the other nine years from somewhere.” 

By using this reasoning, the scientific group discovered a method to accelerate time.

They found that identical physical systems may exchange evolutionary time. You may take one year from each of the first nine systems in an experiment with ten systems over the course of a year and give them all to the tenth. The tenth system will be 10 years old by the end of the year, while the other nine will stay unchanged from the start of the experiment.

This discovery is noteworthy because it adds another twist to the quantum realm, which underpins our knowledge of the cosmos. Philip Walther, though, thinks it also has applications in real life.

“We are convinced that it has technological applications. For example, a rewind protocol in quantum processors can be used to reverse unwanted errors or developments.”

They added, “Further research could include non-optical implementations of the protocol and extensions to higher dimensions.”

Navascués isn’t sure how useful the discovery will be in the real world, but he still thinks their research is a huge success.

“We have made science fiction come true!”

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