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Researchers Demonstrate Time Reversal in Quantum SystemsResearchers Demonstrate Time Reversal in Quantum Systems

The breakthrough has the potential to change how scientists ponder the idea of time itself as well as present an automated way to correct errors in computing or data-transmission systems. There could even be potential relevance for common technologies such as smartphones and batteries.

Elizabeth Montalbano

March 21, 2023

4 Min Read
Time Reversal in Quantum Systems Philip Walther PQ .jpg
Image source: Rafaela Proell/University of Vienna

Researchers have made a potentially game-changing breakthrough in quantum computing—and the application of quantum science itself—with the discovery that they can reverse the direction of time in quantum systems. The discovery paves the way for novel processes in quantum computing as well as how scientists apply these systems to real-world applications, they said.

A team of scientists has discovered that they can reverse processing steps in a quantum system without knowing what the previous steps were, something that isn't typically possible in computing or engineering scenarios, Philip Walther, a professor of physics, at University of Vienna told Design News.

"We realized … that actually in quantum mechanics you can undo reverse processing steps even if you don't know what they look like," he said in an interview. "And that is something that is very atypical. Normally you need to know what happened in a system to undo an evolution."

This discovery adds to knowledge researchers already have amassed about the quantum realm, which operates differently from the rules that typically apply not only in computing and engineering systems, but also in the observable world.

Turning Back Time, Sort Of

In a collaboration between the University of Vienna and IQOQI Vienna, experimental physicists led by Walther successfully implemented what they call a "universal rewinding protocol," which they outlined in a paper published in the journal Optica. The protocol originally was developed by theoretical physicists led by Miguel Navascués, group leader and a researcher from the Institute for Quantum Optics and Quantum Information in Vienna. 

Researchers combined this novel theoretical protocol with an intricate optical setup—implementing ultra-fast optical fiber components and free-space interferometers arranged as a quantum switch—to demonstrate that it is indeed possible to revert changes of a quantum system.

In their proof of concept, researchers successfully reversed the time evolution of a single photon without knowing how it changed in time, or even what its initial and final states were, findings that researchers reported in a paper published in Optica.

The breakthrough is important for a number of reasons. One of them is that it seems to defy the rules of the quantum realm itself, as one of its core principles is that simply observing the system causes it to change. This, in theory, makes it impossible to track a system's changes and reverse the process.

To achieve the rewinding protocol then required using a mathematical trick inserted in the beginning of a process that reverses how it evolves in quantum mechanics, Walther told Design News. "We put in the beginning a mathematical operation with another number that undoes the evolution even if you don't know [what the steps are]," he said.

This trick allows the undoing of an evolution of quantum systems "if you take another evolution and you quantum-mechanically let those things be processed together so it technically achieves that the system goes back to its beginning," Walther explained.

Applications in Computing and Beyond for Time Reversal in Quantum Systems

Knowing now that a universal rewinding protocol exists has implications not only for quantum computing, but also for the relationship between quantum mechanics and other laws of physics and the natural world, Walther said.

Scientifically, one potential application for the protocol could be as the basis for automated error correction in computing or data-transmission systems, eliminating the current need for developers or designers to go back and retrace steps when an error is discovered to fix it, he told Design News.

"This concept, smartly implemented, might allow automatic correction for these errors," Walther said.

Indeed, some of the initial applications of the overall benefits of what researchers are learning about the quantum realm might appear not in the supercomputers that scientists are currently using to explore quantum computing, but in more common technologies such as smartphones or batteries, he said.

"Personally I think that the big breakthrough will be some small idea or device that will find a way to our smartphones or handhelds, or we learn for some reason that you can make future batteries 100 times better," Walther said.

However, it's also entirely possible that the first application of the protocol will be something that appears to come completely out of the blue. "I would not be surprised if some application shows up that we haven't even thought of that leverages this capability," he said.

The bigger-picture impact of the discovery is that the potential to inspire scientists to further explore the nature of time itself as well as glean fundamental insights into quantum mechanics and how they interplay the natural world, he added.

About the Author(s)

Elizabeth Montalbano

Elizabeth Montalbano has been a professional journalist covering the telecommunications, technology and business sectors since 1998. Prior to her work at Design News, she has previously written news, features and opinion articles for Phone+, CRN (now ChannelWeb), the IDG News Service, Informationweek and CNNMoney, among other publications. Born and raised in Philadelphia, she also has lived and worked in Phoenix, Arizona; San Francisco and New York City. She currently resides in Lagos, Portugal. Montalbano has a bachelor's degree in English/Communications from De Sales University and a master's degree from Arizona State University in creative writing.

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