In our everyday world, time is always moving forward. A glass that falls on the floor and breaks does not reassemble and bounces back on the table. In the quantum world – as so often – things are different: Viennese physicists have now succeeded in making a quantum system – not only theoretically, but also in a practical experiment – run back time and return its development to its original state.
Theoretical physicist Miguel Navascues of the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences (ÖAW) in Vienna has devised a so-called “rewind protocol”. It allows one to detect changes in a quantum system through an elegant mathematical trick through the Time inverted – and without knowing what it originally looked like.
“One of the most difficult experiments”
The team led by Philip Walther of the University of Vienna and IQOQI has now succeeded in experimentally realizing this theoretical recipe – using ultra-fast fiber optic components and a special interferometer. The quantum system is a single photon (particle of light) whose polarization (orientation) is changed several times. “It was one of the most difficult experiments we’ve ever set up for a single photon,” Walther explained to the APA.
To implement the theoretical recipe, the physicists superimposed this development of the photon on a second operation — also a change in polarization — “so that we no longer know which of the two processes comes first,” says Walther. They were able to do that thanks to the double application of this so-called quantum switch Time to make it run backwards and the light particle returned to the state it had at the beginning of its journey. It is noteworthy that one does not need to know how the photon interacts with the Time changed, what caused this change and what the initial and final state of the light particle was.
Practical application: undo mistakes
The researchers are convinced that this experiment could also lead to “a technological application” in the future. If you build such a “rewind protocol” into quantum processors in computers for very complex computational tasks, you could use it to undo mistakes or developments that you don’t want.
Source: Krone
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