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.
Quantum Second Law Emerges
More than 200 years after French physicist Sadi Carnot introduced the second law of thermodynamics, scientists have uncovered a strikingly similar rule in the quantum world. A team of international researchers has discovered what they’re calling a second law of entanglement manipulation.
This new law shows that quantum entanglement, a phenomenon at the heart of quantum mechanics, can be reversibly manipulated, much like how heat or energy behaves in thermodynamics. Until now, many experts believed such reversibility was impossible. The findings, published on July 2, 2025, in Physical Review Letters, offer powerful new insights into the basic nature of entanglement and how it might be harnessed more effectively in future quantum technologies.
Entanglement is one of the most fascinating and essential features of quantum physics. When two particles are entangled, measuring one instantly tells you something about the other, even if they’re separated by vast distances. This strange connection was first proposed about 90 years ago as a challenge to the idea that quantum theory could fully describe reality. Today, it’s widely accepted and forms the foundation of quantum information science. Entanglement enables quantum teleportation, secures communication through quantum cryptography, and promises major advances in computing, sensing, and more.
Although entanglement still seems strange to everyday intuition, researchers have found surprising links between entanglement and thermodynamics—the science of heat and energy. One example is something called “entanglement entropy,” a property of ideal quantum systems that closely mirrors how entropy works in classical thermodynamics. These parallels are helping scientists build a deeper, more unified understanding of the quantum universe.
Chasing Reversible Entanglement
However, an equivalent to the second law of thermodynamics, which dictates that processes tend towards increasing disorder (the aforementioned entropy) and that perfect reversibility is an attainable though rare and highly efficient ideal, has remained stubbornly out of reach. Here, reversibility does not refer to time symmetry but the ability of an external agent to manipulate the system into a different state and then manipulate it back to its initial state without any loss. “Finding a second law analogous to the second law of thermodynamics has been an open problem in quantum information science,” says study co-author Tulja Varun Kondra. “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. This limitation to local operations and classical communication (LOCC) simplifies the situation, meaning whatever Alice and Bob do, they cannot affect the intrinsically nonlocal properties of entanglement between their quantum systems.
“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.
Powering Transformations with Entanglement Batteries
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. But a more important outcome of this work is that the researchers have shown that the methods they have developed are applicable beyond mixed-state entanglement transformation, allowing them to leverage the entanglement battery to verify reversibility in various scenarios. Proving that entanglement manipulations across all quantum states are reversible is expected to lead to a family of second laws for entanglement manipulation.
Beyond Entanglement: Resource Batteries
The entanglement battery may even find uses outside entanglement theory. For example, the same principles apply to systems involving more than two entangled particles, paving the way for understanding and manipulating complex quantum networks and perhaps developing future, highly efficient quantum technologies.
In addition, generalising the concept of an entanglement battery to a resource battery – an additional quantum system that participates in the transformation process without reducing the resource in question – could allow the systematic demonstration of reversibility across quantum physics based on a minimal set of assumptions. “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,” says Streltsov. “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.”
Reference: “Second Law of Entanglement Manipulation with an Entanglement Battery” by Ray Ganardi, Tulja Varun Kondra, Nelly H. Y. Ng and Alexander Streltsov, 2 July 2025, Physical Review Letters.
DOI: 10.1103/kl56-p2vb
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5 Comments
Scientists have discovered a way to make quantum entanglement reversible, something long thought to be impossible, the findings, published on July 2, 2025, in Physical Review Letters.
Please ask scientists to think deeply:
In today’s physics and so-called peer-reviewed publications, what is possible and what is impossible?
Defying empirical distinctions by defining the manifestly different θ and τ particles as identical. Two sets of artificially counter-rotating Co-60—whether symmetric or not—constitute mirror objects to each other. Perhaps only so-called peer-reviewed publications such as Nature, Science, and the Physical Review series would dare to act with such recklessness and shamelessness.
If you believes the evidence, please browse https://zhuanlan.zhihu.com/p/1925124100134790589 (If the link is not blocked).
The current state of physics and so-called top-tier or authoritative publications—with their visible and hidden corruptions and ugliness—has become truly shocking. Those peer-reviewed publications that mislead science and the public in the name of academia are even more despicable than ordinary publications.
☑️☑️
Article could be clearer and writing more direct and logical.
I learned nothing from this article about what this battery supposedly does or how it works. This all seems very vague and click-baity. This site has extremely tempting article links, for which I give them credit. But do the articles live up to the hype?