No Second Law
An Anonymous Coward writes:
https://scitechdaily.com/scientists-prove-that-there-is-no-second-law-of-entanglement/
The second law of thermodynamics is widely considered one of the most universally true physical laws. It dictates that the entropy, a measure of physical disorder, of any isolated system can never decrease over time. It adds an 'arrow of time' to everyday occurrences, determining which processes are reversible and which are not. It explains why an ice cube on a hot stove will always melt and why compressed gas will always escape its container and never return when a valve is opened to the atmosphere.
Only states of equal entropy and energy can be reversibly converted from one to the other. This reversibility condition led to the discovery of thermodynamic processes such as the (idealized) Carnot cycle, which poses an upper limit to how efficiently one can convert heat into work, or the other way around, by cycling a closed system through different temperatures and pressures. Our understanding of this process underpinned the rapid economic development during the Western Industrial Revolution.
[...] Resolving this long-standing open question, research carried out by Lami (previously at the University of Ulm and currently at QuSoft and the University of Amsterdam) and Bartosz Regula (University of Tokyo) demonstrates that manipulation of entanglement is fundamentally irreversible, putting to rest any hopes of establishing a second law of entanglement. This new result relies on the construction of a particular quantum state which is very 'expensive' to create using pure entanglement. Creating this state will always result in a loss of some of this entanglement, as the invested entanglement cannot be fully recovered. As a result, it is inherently impossible to transform this state into another and back again. The existence of such states was previously unknown.
Because the approach used here does not presuppose what exact transformation protocols are used, it rules out the reversibility of entanglement in all possible settings. It applies to all protocols, assuming they don't generate new entanglement themselves. Lami explains: "Using entangling operations would be like running a distillery in which alcohol from elsewhere is secretly added to the beverage."
Journal Reference:
Lami, L., Regula, B. No second law of entanglement manipulation after all. Nat. Phys. 19, 184-189 (2023). https://doi.org/10.1038/s41567-022-01873-9
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