Evaluating the maximum amount of work extractable from a nanoscale quantum system is one of the central problems in quantum thermodynamics. Previous works identified the free energy of the input state as the optimal rate of extractable work under the crucial assumption: experimenters know the description of the given quantum state, which restricts the applicability to significantly limited settings. Here, we show that this optimal extractable work can be achieved without knowing the input states at all, removing the aforementioned fundamental operational restrictions. We achieve this by presenting the construction of a quantum channel whose description does not depend on input states but nevertheless extracts work quantified by the free energy of the unknown input state. Remarkably, our result partially encompasses the case of infinite-dimensional systems, for which optimal extractable work has not been known even for the standard state-aware setting. Our results clarify that, even though whether the description of the given state is provided at the beginning of the protocol generally makes the operational setting fundamentally different in accomplishing information-theoretic tasks, not knowing the input state does not influence the optimal performance of the asymptotic work extraction. The maximum work extracted from independent and identically distributed quantum states is characterised only in the state-aware scenario, and it remains unknown with no prior knowledge of the state. Here, the authors show that optimal work extraction can be achieved by a single operation, referred as universal work extraction.

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A new universal work extraction protocol for quantum thermodynamics is presented, showing that optimal work can be extracted from nanoscale quantum systems without any prior knowledge of the input quantum state. Previous results required experimenters to know the full description of the quantum state, limiting practical applicability. The authors construct a quantum channel independent of the input state that still achieves the optimal work extraction rate characterized by Helmholtz free energy (via relative entropy). The result extends to infinite-dimensional systems (e.g., bosonic/quantum optical systems), where even the state-aware optimal rate was previously unknown. The protocol leverages Schur-Weyl duality and permutation symmetry to diagonalize states without learning their full description, using a Schur pinching channel followed by incoherent measurement-based estimation of relative entropy. The work also connects to quantum resource theory, pseudo-resource states, and universal entanglement distillation.

Universal work extraction in quantum thermodynamics