An information-thermodynamic framework explains how to extract work from complex quantum systems initially in microscopic thermal equilibrium; it advances beyond limitations preventing full exploitation of these states’ potential. Under realistic conditions, local measurements and feedback controls acting on nearby areas yield maximum obtainable work that matches predictions based on standard thermodynamic principles governing mixed quantum states. This clarifies how much useful energy can be obtained from complex quantum systems when measurements are limited to local areas and controls happen quickly; it builds on existing understanding of information thermodynamics.

Under these realistic conditions, extracting work follows established rules for mixed quantum states, where knowledge is incomplete. The RIKEN research team has established an information-thermodynamic framework to understand how useful energy can be drawn from complex quantum systems initially in what they term ‘microscopic thermal equilibrium’. Imagine this initial state like a perfectly shuffled deck of cards; each card represents an energy level and being thoroughly mixed means all arrangements are equally probable. This clarifies limits on extracting energy when only observing small areas of these systems.

Local Measurements Unlock Enhanced Work Extraction From Quantum Systems

A gain exceeding the limits of standard thermodynamics occurred when extractable work from closed quantum systems matched their corresponding canonical ensembles under local measurements. This breakthrough overcomes a long-standing threshold that previously limited full exploitation of microscopic thermal equilibrium states, states reliant only on unitary operations. Now, distant measurement feedback unlocks hidden correlations within these complex systems, boosting energy extraction.

Quantifiable measures like ‘quantum-classical mutual information’ rigorously define how much useful energy can be obtained with restricted observations and fast controls; this framework allows for an extensive increase in harvested energy as system size grows, even beyond those canonical ensemble limits. Specifically, extracted work matches what is achievable using statistical averages over many identical systems measured locally and controlled quickly while neglecting minor corrections scaling slower than system volume. The additional power stems from exploiting connections within the quantum state.

Quantifying Information Gain from Local Quantum Measurements

A technique quantifying information gained through measurements provides a key to understanding work extraction from complex quantum systems, building on existing ideas about knowledge’s impact on thermodynamics, akin to Maxwell’s demon. Closed many-body systems starting in ‘microscopic thermal equilibrium’ were carefully modelled; this initial state resembles a perfectly shuffled deck of cards where all energy arrangements are equally probable.

Restrictions applied only to *local* measurements observing small areas and rapid controls enacted by nearby interactions. The team examined finite-time control using local Hamiltonians instead of methods allowing arbitrary global unitaries impractical for current quantum computers and simulators.

This approach allowed them to understand how localized actions influence work extraction, expressing achievable work with quantifiable measures like ‘quantum-classical mutual information’ and ‘Holevo information’, concepts relating shared knowledge about the system.

Distant Measurements Enhance Quantum Work Extraction Through System Interconnectedness

Researchers from RIKEN and The University of Tokyo have established a framework explaining how to coax energy out of complex quantum systems initially balanced at microscopic thermal equilibrium, imagining countless particles each possessing an equal chance of having any given amount of energy. Their findings confirm that maximum work under local control aligns with standard thermodynamic expectations; however, distant measurements unlock additional power by exploiting hidden connections within these states. Defining useful extracted energy requires representing all possible arrangements as equally probable in complex quantum systems at microscopic thermal equilibrium.

This research developed a framework for understanding how information impacts the extraction of work from closed quantum many-body systems starting in microscopic thermal equilibrium. The team rigorously demonstrated that, under restrictions of local measurements and controls, the amount of extractable work matches what is predicted by standard thermodynamics.

👉 More information
🗞 Information Thermodynamics in Closed Quantum Many-Body Dynamics
✍️ Yusuke O. Nakai (Affiliation: RIKEN Center for Emergent Matter Science); Shoki Sugimoto (The University of Tokyo); Ryusuke Hamazaki (RIKEN Pioneering Research Institute)
🧠 ArXiv: https://arxiv.org/abs/2611.16329

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