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While quantum entanglement mimicks the first law of thermodynamics in terms of entropy in a system, scientists wonder if the second law—especially the part about reversibility—could hold true.
A new study uses a quantum battery that stores quantum entanglement information.
Scientists successfully reversed mix-state quantum entanglement, which could improve the manipulation and efficiency of future quantum systems.
The worlds of quantum and classical physics seldom get along. Take, for instance, the concept of quantum entanglement. The central feature of quantum mechanics, entanglement, details how the information of two particles can correlate with each no matter the distance. This idea is so strange in the classical sense that Albert Einstein famously labeled the idea “spooky action at a distance” and left it at that.
However, a new study explores how the rules of quantum entanglement do have a classical counterpart of a sort: the laws of thermodynamics. In an idealized quantum system, for example, entanglement does feature a kind of entropy analogous to the first law of thermodynamics.
Now, scientists wonder if the second law—that perfect reversibility is possible in a highly efficient ideal system—could also apply to entanglement, and a team of researchers thinks they may have an answer thanks to a high-tech workaround: quantum batteries. The results of the study were published in the journal Physical Review Letters.
“Finding a second law analogous to the second law of thermodynamics has been an open problem in quantum information science,” Tulja Varun Kondra, a former University of Warsaw Ph.D. student and study co-author now working at Heinrich Heine University Düsseldorf, said in a press statement. “Solving this has been our primary motivation.”
Most scenarios designed to investigate reversibility focus on two particles (usually nicknamed Alice and Bob), but are restricted locally and must act through classical means, such as the internet. These are known as local operations and classical communication (LOCC) operations, and so far, scientists have discerned that in this scenario, entanglement is indeed irreversible. To find out if this was a universal rule, the authors needed to dig deeper by “somehow go[ing] beyond LOCC in a meaningful way and recover[ing] reversibility,” according to Varun Kondra.
The team succeeded by introducing another party to this quantum duo known as a “quantum battery.” Just as a normal battery stores thermodynamic energy, a quantum battery stores entanglement. The authors say that this battery ensures no net entanglement is lost, and when assisting with LOCC operations, mixed-state entanglement transformations can be perfectly reversible.
“We can have a battery that is supposed to preserve coherence or free energy, and then we can formulate a reversible framework in this setting where, instead of entanglement, we reversibly manipulate that particular resource of our system,” Streltsov said. “Though many of these other principles of reversibility have already been confirmed via other approaches, our technique offers a unified proof framework based on well-established physical principles.”
The authors said that proving reversibility across various quantum scenarios could open a whole “family” of second laws for quantum manipulation. They also hope that future research will use reversibility to create more highly efficient quantum technologies.
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