Scientists have discovered a way to make quantum entanglement reversible, something long thought to be impossible, via a quantum entanglement battery device

> Scientists have discovered a way to make quantum entanglement reversible, something long thought to be impossible, by using a conceptual device called an entanglement battery. Much like a regular battery stores energy, this theoretical tool can **store and release entanglement, allowing quantum states to be transformed and reversed without loss.** This breakthrough reveals a new “second law” for quantum mechanics, echoing the principles of thermodynamics and opening the door to more efficient quantum technologies and a unified framework for manipulating quantum resources.

> “Finding a second law analogous to the second law of thermodynamics has been an open problem in quantum information science, solving this has been our primary motivation.” Much work towards addressing this problem has focused on a scenario in which two distant parties (often called Alice and Bob) want to exchange quantum information, but are restricted to act locally on their quantum systems and communicate classically, by say phone or the internet. “It is known that under LOCC operations in this scenario, entanglement is irreversible,” explains lead author of the study Alexander Streltsov. “So the question is, can we somehow go beyond LOCC in a meaningful way, and recover reversibility?” The team’s answer is ‘yes’, **as long as Alice and Bob share an additional entangled system: an entanglement battery.**

> Just as an ordinary battery stores energy that can be used to inject or store work in the context of thermodynamics, an entanglement battery injects and stores entanglement. The battery can be used in the state transformation process and the state of the battery itself can be changed to perform operations. There is only one rule: whatever Alice and Bob do, **they must not decrease the level of entanglement within the battery.**

> And just as a regular battery allows tasks to be performed that would be impossible without one, so too does an entanglement battery. By assisting standard LOCC operations with their hypothetical entanglement battery, **the team demonstrated that any mixed-state entanglement transformation can be made perfectly reversible.**

> This achievement is a significant contribution to the debate around whether entanglement manipulation is generally reversible.

I thought quantum processes are reversible by definition,  other than decoherence?