Artificially intelligent Maxwell's demon for optimal control of open quantum systems scirate.com/arxiv/2408.15328 We take an agent in reinforcement machine learning literally and explore the implications for quantum thermodynamics: it automates the role of a quantum Maxwell’s demon.
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Feedback control of #openquantumsystems is of fundamental importance for practical applications in various contexts, ranging from #quantumcomputation to quantum error correction and quantum metrology. Its use in the context of #thermodynamics further enables the study of the interplay between information and energy. However, deriving optimal #feedback control strategies is highly challenging, as it involves the optimal control of open quantum systems, the stochastic nature of quantum #measurement, and the inclusion of policies that maximize a long-term time- and trajectory-averaged goal. In this work, we employ a #reinforcementlearning approach in #machinelearning to automate and capture the role of a quantum @Maxwell's demon: the #agent takes the literal role of discovering optimal feedback control strategies in qubit-based systems that maximize a trade-off between measurement-powered cooling and measurement efficiency. Considering weak or projective quantum measurements, we explore different regimes based on the ordering between the thermalization, the measurement, and the unitary feedback timescales, finding different and highly non-intuitive, yet interpretable, strategies. In the thermalization-dominated regime, we find strategies with elaborate finite-time thermalization protocols conditioned on measurement outcomes. In the measurement-dominated regime, we find that optimal strategies involve adaptively measuring different qubit observables reflecting the acquired information, and repeating multiple weak measurements until the quantum state is "sufficiently pure", leading to random walks in state space. Finally, we study the case when all timescales are comparable, finding new feedback control strategies that considerably outperform more intuitive ones. We discuss a two-qubit example where we explore the role of entanglement and conclude discussing the scaling of our results to quantum many-body systems.

Aug 29, 2024 · 3:41 AM UTC

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Warm thanks to the coauthors, in particular to Paolo Andrea Erdman and Giacomo Guarnieri. It is also my first paper together with the great colleague @FrankNoeBerlin.
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And thanks to our funders, specifically at @dfg_public, the @ERC_Research, and the @BMBF_Bund (@QuantenTech).
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