2025-11-14 京都大学
本研究で導出したトレードオフ関係式の概念図。観測確率をゼロにする熱力学過程では、時間・コスト・エラーの間に普遍的なトレードオフ関係が生じる。代表的な例として、冷却、情報の消去、コピーなどが挙げられる。
＜関連情報＞
- https://www.kyoto-u.ac.jp/ja/research-news/2025-11-14
- https://www.kyoto-u.ac.jp/sites/default/files/2025-11/web_2511_Saito-1dadf5f484f3fe3aab5068d7efbcda67.pdf
- https://journals.aps.org/prx/abstract/10.1103/l6b9-rg1j
熱力学における時間・コスト・誤差のトレードオフ関係：第三法則とその先 Time-Cost-Error Trade-Off Relation in Thermodynamics: The Third Law and Beyond
Tan Van Vu and Keiji Saito
Physical Review X Published: 13 November, 2025
DOI: https://doi.org/10.1103/l6b9-rg1j
Abstract
Elucidating fundamental limitations inherent in physical systems is a central subject in physics. For important thermodynamic operations such as information erasure, cooling, and copying, resources like time and energetic cost must be expended to achieve the desired outcome within a predetermined error margin. In the context of cooling, the unattainability principle of the third law of thermodynamics asserts that infinite “resources” are needed to reach absolute zero. However, the precise identification of relevant resources and how they jointly constrain achievable error remains unclear within the frameworks of stochastic and quantum thermodynamics. In this work, we introduce the concept of separated states, which consist of fully unoccupied and occupied states, and formulate the corresponding thermokinetic cost and error, thereby establishing a unifying framework for a broad class of thermodynamic operations. We then uncover a three-way trade-off relation between time, cost, and error for thermodynamic operations aimed at creating separated states, simply expressed as τCετ ≥ 1 − η. This fundamental relation is applicable to diverse thermodynamic operations, including information erasure, cooling, and copying. It provides a profound quantification of the unattainability principle in the third law of thermodynamics in a general form. Building upon this relation, we explore the quantitative limitations governing cooling operations, the preparation of separated states, and a no-go theorem for exact classical copying. Furthermore, we extend these findings to the quantum regime, encompassing both Markovian and non-Markovian dynamics. Specifically, within Lindblad dynamics, we derive a similar three-way trade-off relation that quantifies the cost of achieving a pure state with a given error. The generalization to general quantum dynamics involving a system coupled to a finite bath implies that the dissipative cost becomes infinite as the quantum system is exactly cooled down to the ground state or perfectly reset to a pure state, thereby resolving an open question regarding the thermodynamic cost of information erasure.
