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Japan: quantum foundations of thermodynamics

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Japanese quantum framework specifies conditions for the second law

RIKEN and university partners presented a theoretical framework linking quantum mechanics to the second law of thermodynamics on 4 November 2026. The study appeared in PRX Quantum on 3 November, or 4 November in Japan, according to the release.

RIKEN in Wakō, 21 April 2007. Institutional archive; does not depict the theoretical study. TAKASHI / adaptation by Kozo, CC BY-SA 3.0; no additional changes.
RIKEN in Wakō, 21 April 2007. Institutional archive; does not depict the theoretical study. TAKASHI / adaptation by Kozo, CC BY-SA 3.0; no additional changes. — TAKASHI / adaptation by Kozo / Wikimedia Commons — CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0/ ; 21 April 2007; no additional changes.

The team defines thermal equilibrium and macroscopic operations using quantities such as energy and magnetization. It introduces a quantum entropy compatible with thermodynamic entropy within that framework, including for some pure quantum states.

The authors derive two formulations of the second law, including entropy non-decrease under the studied conditions. This is a mathematical proof, with no new experimental device announced.

RIKEN specifies a limitation: the proof concerns operations whose duration does not increase with system size. Extending it to longer operations requires further conditions; the result is not an assumption-free proof covering every physical situation.

Sources 3