Entanglement Battery Unlocks Lossless Quantum State Conversions

In the resource theory of entanglement, we've asked ourselves for some time now: what does it take to interconvert between different entangled states reversibly, i.e. without loss, at the very least so in the asymptotic limit of many copies? For some time, the main answer to this question was that this can be done with asymptotically non-entangling operations, and the proof was via the generalized quantum Stein's lemma. However, recent scrutiny raised questions about the validity of this lemma, casting uncertainty on the quest of reversibility.

Together with Ray, Varun, Alex, we show that a very simple recipe exists that can recover reversibility. Importantly, this recipe makes use of entanglement battery—a tool that temporarily stores and supplies entanglement. One can see this s a relaxed notion of catalysis where instead of asking for the catalyst to remain unchanged, we simply request that the entanglement content within the battery doesn't decrease after facilitating the process. Interesting, with simple LOCC operations and access to an entanglement battery, one can show that entanglement manipulation becomes reversible for all quantum states!

This result has been accepted for publication in Physical Review Letters.