A gondolier is trapped in a quantum superposition. The University of Vienna and the Institute for Quantum Optics are part of the Austrian Academy of Sciences.
A team of physicists at the Universities of Bristol, Vienna, the Balearic Islands, and the Institute for Quantum Information (IQOQI-Vienna) has shown how quantum systems can evolve along two opposite time arrows.
The study, published in the latest issue of Communications Physics, necessitates a rethink of how the flow of time is understood and represented in contexts where quantum laws play a crucial role.
Philosophers and physicists have pondered the existence of time for hundreds of years. In the classical world, our experience seems to make up for any doubts about time. In nature, processes tend to evolve spontaneously from states with less disorder to states with more disorder, and this propensity can be used to identify an arrow of time. This is described in terms of 'entropy', which is the physical quantity defining the amount of disorder in a system.
Dr. Giulia Rubino is the lead author of the publication.
If a phenomenon produces a large amount of entropy, observing its time-reversal is impossible. There is a non-negligible chance of seeing the time-reversal of a phenomenon occur naturally if the entropy is small.
We can use the sequence of things we do in the morning as an example. If we were shown our toothpaste moving from the toothbrush to the tube, it would be a replay of our day. If we squeezed the tube gently, we wouldn't be able to see the toothpaste reentering the tube.
The principle of quantum superposition was applied to the quantum realm by the authors of the study, under the leadership of Professor Caslav Brukner of the University of Vienna and the IQOQI-Vienna.
The toothpaste coming out of or going back into the tube can also be evolving simultaneously along both temporal directions if this principle is extended to time's arrows.
The laws of the universe are based on quantum-mechanical principles, and this idea seems rather nonsensical when applied to our day-to-day experience. Dr. Rubino wondered why we never encounter these superpositions of time flows in nature.
The University of the Balearic Islands co-author said that they quantified the entropy produced by a system evolving in quantum superposition of processes with opposite time arrows. The most likely process of the two was the one that resulted in projecting the system onto a well-defined time's direction. One can observe the consequences of the system having evolved along the forward and backward temporal directions at the same time when small amounts of entropy are involved.
The work has practical implications in quantum thermodynamics, as well as the fundamental feature that time might not be well-defined. The performance of thermal machines and refrigerators could be improved by placing a quantum system in a superposition of alternative time's arrows.
Rubino said that the laws governing time in quantum mechanical contexts are more complex than they are thought. This may suggest that we need to rethink the way we represent this quantity in all those contexts.
The paper "Quantum superposition of thermodynamic evolutions with opposing time's arrows" was published in Communications Physics.
Communications physics has more information about quantum superposition of thermodynamic evolutions. There is a DOI titled " 10.1038/s42005-021-00759-1".
Journal information about communications physics.
Time flows in the quantum realm are not what you might expect.
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