We present a fully autonomous model of a mechanical Maxwell demon engine that converts heat absorbed by a qubit into population inversion in an attached quantum battery. A damped mechanical oscillator acts as a pointer that incorporates the essential demon function of information acquisition about the qubit state and subsequent feedback into the system dynamics, replacing external measurements and control operations. This is achieved by means of a Holstein-type Hamiltonian, which makes the pointer's equilibrium position depend on the qubit state and thereby induces a state-dependent resonance shift. The mechanism enables a selective energy transfer to an attached spin system that acts as the quantum battery. We derive both local and global Lindblad master equations for the coupled system and identify the parameter regimes in which the engine operates efficiently. The figure of merit is the resulting steady-state population inversion of the battery, quantified in terms of ergotropy. Based on these results, we discuss the necessary conditions for practical implementations of the demon engine on realistic experimental platforms.
We present a fully autonomous model of a mechanical Maxwell demon engine that converts heat absorbed by a qubit into population inversion in an attached quantum battery. A damped mechanical oscillator acts as a pointer that incorporates the essential demon function of information acquisition about the qubit state and subsequent feedback into the system dynamics, replacing external measurements and control operations. This is achieved by means of a Holstein-type Hamiltonian, which makes the pointer's equilibrium position depend on the qubit state and thereby induces a state-dependent resonance shift. The mechanism enables a selective energy transfer to an attached spin system that acts as the quantum battery. We derive both local and global Lindblad master equations for the coupled system and identify the parameter regimes in which the engine operates efficiently. The figure of merit is the resulting steady-state population inversion of the battery, quantified in terms of ergotropy. Based on these results, we discuss the necessary conditions for practical implementations of the demon engine on realistic experimental platforms.
We discuss a self-contained spin-boson model for a measurement-driven engine, in which a demon generates work from thermal excitations of a quantum spin via measurement and feedback control. Instead of granting it full direct access to the spin state and to Landauer's erasure strokes for optimal performance, we restrict this demon's action to pointer measurements, i.e., random or continuous interrogations of a damped mechanical oscillator that assumes macroscopically distinct positions depending on the spin state. The engine can reach simultaneously the power and efficiency benchmarks and operate in temperature regimes where quantum Otto engines would fail.
I study an autonomous quantum Maxwell's demon based on two exchange-coupled quantum dots attached to the spin-polarized leads. The principle of operation of the demon is based on the coherent oscillations between the spin states of the system which act as a quantum iSWAP gate. Due to the operation of the iSWAP gate, one of the dots acts as a feedback controller which blocks the transport with the bias in the other dot, thus inducing the electron pumping against the bias; this leads to the locally negative entropy production. Operation of the demon is associated with the information transfer between the dots, which is studied quantitatively by mapping the analyzed setup onto the thermodynamically equivalent auxiliary system. The calculated entropy production in a single subsystem and information flow between the subsystems are shown to obey a local form of the second law of thermodynamics, similar to the one previously derived for classical bipartite systems.
Subsystems of a composite system in a pure state generally exist in mixed states and undergo changes with the overall state. This phenomenon arises from the coherence of the entire system and represents a crucial distinction between quantum and classical systems. Such a quantum property can enhance the work output of an Otto heat engine composed of two qubits, whose parameters evolve in opposite directions. When the energy levels of the two qubits are identical at one of the thermal equilibrium states of the Otto cycle and there is no interaction between them, the total work output is strictly negative, which is guaranteed by the second law of thermodynamics. However, the interaction-induced coherence allows for positive work output under such conditions. Our model provides an autonomous implementation of Maxwell’s demon, where the measurement and feedback operations are driven by an adiabatically evolved Hamiltonian without external intervention. Furthermore, the coherence of the entire system is amplified by the heat reservoir after measurement, which is the key of the positive work output. Conversely, the quantum measurement-erase cycle typically outputs negative work, attributed to the decoherence of the instrument during the measurement process.
We propose a protocol for extracting work from a coherent quantum battery state by exploiting measurement-assisted feedback mediated by a continuous-variable pointer. The scheme relies on the unitary operator U=exp(−iktH^⊗P^/ℏ), which generates entanglement between the battery's energy eigenstates and the position of an auxiliary pointer. A subsequent projective measurement of the pointer's position conditionally prepares the battery in a pure state from which work can be extracted via a feedback unitary. We analyze the protocol for a two-level quantum battery and a Gaussian pointer, computing the conditional states and the corresponding daemonic ergotropy. For the pure initial state considered, we find that the daemonic ergotropy equals the standard ergotropy for all interaction strengths, demonstrating that the measurement-assisted feedback recovers the full extractable work that would otherwise become inaccessible due to entanglement with the pointer when its degrees of freedom are traced out. The protocol thus provides a physically transparent realization of a quantum Maxwell demon, where the pointer acts as a quantum measurement ancilla whose position becomes correlated with the battery's energy. The scheme is amenable to experimental implementation in trapped-ion systems, and it contributes to the ongoing efforts to understand the role of quantum coherence and measurement in thermodynamics.
We present a unified theoretical, numerical, and experimental investigation into autonomous information heatengines (Maxwell’s demons), bridging microscopic open quantum thermodynamics, stochastic continuous moni-toring, deep reinforcement learning, and practical energy harvesting engineering. First, addressing widespreadnumerical pitfalls in quantum thermodynamics simulations, we identify an operator sign inversion in detailed-balance jump rates that previously simulated an unphysical “perpetual motion machine” yielding −19.29 kB T .Once corrected via adaptive Runge-Kutta integration, we prove that single-step work extraction from maximallyentangled Bell states is strictly bounded by kB T ln 2, and that the cyclic entropy accounting of entanglement re-generation imposes a net non-negative work cost (Wnet ≥ 0), establishing quantum entanglement as a consumedthermodynamic fuel rather than a violation of the Second Law. Second, using positive-preserving Rouchon-Ralphstochastic master equation mappings across 48 trajectory ensembles, we evaluate an Information Conveyor Beltin a 10-dot chain under continuous homodyne detection. We demonstrate that while an isolated cryogenic demonreservoir (TM = 4.2 K) enables positive extracted power, incorporating the mandatory Carnot refrigeration over-head required to maintain the cryostat exactly cancels all efficiency advantages, yielding an overall system deficitmatching the isothermal baseline. Third, we address autonomous control in partially observable Markov deci-sion processes (POMDPs) by deploying Recurrent Proximal Policy Optimization (Recurrent PPO with LSTM),enabling the demon to autonomously overcome measurement backaction and discover synchronized conveyor trans-port policies superior to classical heuristics. Finally, we design and verify Configuration D, a body-heat-poweredthermoelectric energy harvester operating an ESP32-C3 microcontroller demon. By eliminating idle wake-timedelays and overlapping 9-bit digital sensor conversion with sub-millisecond USB polling, firmware v2 slashes ac-tive controller consumption in our calibrated design model by a factor of 8.7 (from ≈ 208.5 mJ to ≈ 24.1 mJ),establishing a net-positive self-powered operational cycle (+65.8 mJ/cycle). We quantify the fundamental gap of≈ 8.4 × 1018 (≈ 19 orders of magnitude) between the Landauer erasure limit (2.87 × 10−21 J) and real-worldmicrocontrollers, delineating the rigorous boundary between physical information thermodynamics and real-worldenergy harvesting.
We propose and analyze Maxwell's demon based on a single qubit with avoided level crossing. Its operation cycle consists of adiabatic drive to the point of minimum energy separation, measurement of the qubit state, and conditional feedback. We show that the heat extracted from the bath at temperature T can ideally approach the Landauer limit of kBTln2 per cycle even in the quantum regime. Practical demon efficiency is limited by the interplay of Landau-Zener transitions and coupling to the bath. We suggest that an experimental demonstration of the demon is fully feasible using one of the standard superconducting qubits.