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Physical review. B./Physical review. B

Quantum measurement spintronic engine powered by quantum coherence enhanced by bosonic catalysis

Mathieu Lamblin, Martin Bowen

Published Apr 12, 2024• 1 citation
Publisher

Abstract

Quantum information engines can advantageously convert information into work, usually through a feedback mechanism operated by a Maxwell demon. In principle, this opens prospects of autonomous machines that challenge the classical second law of thermodynamics. Yet prior research, which typically tests a given concept in isolation, usually makes strong assumptions on turning on/off internal interactions or the connection to the baths, which has fueled skepticism. Meanwhile, several recent experiments describe an autonomous spintronic engine that purportedly combines several concepts using inherent electronic interactions to harvest spin fluctuations and quantum correlations. So far, no full-fledged theory has described it. In this article, we address these several interdisciplinary shortcomings by presenting a theory for a solid-state, fully electronic spintronic quantum information engine that converts the energy of quantum coherence into useful electrical work thanks to quantum measurements. Our simple two-stroke engine operates on two correlated atomic, single-spin quantum dots (QDs) that are connected in series with two ferromagnetic electrodes. The ultrafast measurement stroke destroys the quantum coherence stored within the QDs and projects the system into a local high-energy separated state. The resulting energy is then released into the leads as electrical current when the partial thermalizing stroke restores quantum coherence. Using a master equation approach, we show that a robust steady-state current can flow between the electrodes despite the absence of a tunneling path and at thermal equilibrium. Our model proves the feasibility of harvesting quantum fluctuations by the measurement back-action through the on-site Coulomb interaction, and can reproduce experimental output power levels if bosons mediate this transport in the presence of an additional nonequilibrium resource. This can for instance be accomplished by the spin bias that is inherently generated by the ferromagnetic electrodes. Our work raises the prospect of measuring the ``spintronic temperature'' of the leads using magnetization dynamics experiments, while the model's underpinnings of built-in, materials-inherent measurements of quantum information can in principle be adapted to describe fundamental quantum processes in chemistry and biology.

DOI
10.1103/physrevb.109.165423

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Quantum information engines can advantageously convert information into work, usually through a feedback mechanism operated by a Maxwell demon. In principle, this opens prospects of autonomous machines that challenge the classical second law of thermodynamics. Yet prior research, which typically tests a given concept in isolation, usually makes strong assumptions on turning on/off internal interactions or the connection to the baths, which has fueled skepticism. Meanwhile, several recent experiments describe an autonomous spintronic engine that purportedly combines several concepts using inherent electronic interactions to harvest spin fluctuations and quantum correlations. So far, no full-fledged theory has described it. In this article, we address these several interdisciplinary shortcomings by presenting a theory for a solid-state, fully electronic spintronic quantum information engine that converts the energy of quantum coherence into useful electrical work thanks to quantum measurements. Our simple two-stroke engine operates on two correlated atomic, single-spin quantum dots (QDs) that are connected in series with two ferromagnetic electrodes. The ultrafast measurement stroke destroys the quantum coherence stored within the QDs and projects the system into a local high-energy separated state. The resulting energy is then released into the leads as electrical current when the partial thermalizing stroke restores quantum coherence. Using a master equation approach, we show that a robust steady-state current can flow between the electrodes despite the absence of a tunneling path and at thermal equilibrium. Our model proves the feasibility of harvesting quantum fluctuations by the measurement back-action through the on-site Coulomb interaction, and can reproduce experimental output power levels if bosons mediate this transport in the presence of an additional nonequilibrium resource. This can for instance be accomplished by the spin bias that is inherently generated by the ferromagnetic electrodes. Our work raises the prospect of measuring the ``spintronic temperature'' of the leads using magnetization dynamics experiments, while the model's underpinnings of built-in, materials-inherent measurements of quantum information can in principle be adapted to describe fundamental quantum processes in chemistry and biology.
Quantum fluctuations, which result from the Heisenberg uncertainty principle, explain a number of physical observations, from the finite mass of elementary particles to the Lamb shift in hydrogen and the Casimir effect. The local violation of the conservation of energy raises the question of whether the energy of quantum fluctuations can sustain the cycle of a quantum engine. So far, a proposal has hinted that this is possible, but contains important caveats. In this Letter, we predict that quantum fluctuations can power an autonomous spintronic quantum information engine by converting entanglement energy into useful electrical work. Our two-stroke engine operates on two entangled spin quantum dots (QDs) that are connected in series with two fully spin-polarized baths. The ultrafast measurement stroke breaks the entanglement, thereby energizing the system on average. This energy is released into the leads as electrical current when the thermalizing stroke equilibrates the QDs with the electrode baths. Using a master equation approach, we analytically demonstrate the efficiency of the quantum fluctuation-driven engine, and we study the cycle numerically to gain insight into the relevant parameters to maximize power. Our results suggest that quantum fluctuations and the measurement back-action alone cannot explain prior experimental results. Measuring the spin dynamics of the engine's ferromagnetic electrodes should help determine its efficiency. This electronically driven feedback on quantum entanglement should also boost quantum chemistry, biology and cognition.
Thermodynamics of information identifies information flow as a thermodynamic resource, but whether quantum coherence and collective coupling can enhance it at low entropy-production cost remains unresolved. We address this question for interacting open quantum systems by deriving a thermodynamic uncertainty relation that bounds information flow in terms of entropy production in nonequilibrium steady states. We construct a quantum engine in which N-fold degenerate ground and excited states are collectively coupled to heat baths. Collective jumps enhance heat currents and information flow linearly with N, while entropy production remains independent of N, realizing a high-power, low-dissipation autonomous quantum Maxwell's demon that leverages collectively enhanced information flow to pump heat against a temperature gradient. Beyond steady states, collective interactions amplify the unitary component of quantum information flow, yielding a quadratic enhancement of the free-energy charging power of quantum batteries. Our results reveal scalable advantages of quantum coherence and collective effects in quantum engines.
In scenarios coined Maxwell's demon, information on microscopic degrees of freedom is used to seemingly violate the second law of thermodynamics. This has been studied in the classical as well as the quantum domain. In this paper, we study an implementation of Maxwell's demon that can operate in both domains. In particular, we investigate information-to-work conversion over the quantum-to-classical transition. The demon continuously measures the charge state of a double quantum dot and uses this information to guide electrons against a voltage bias by tuning the on-site energies of the dots. Coherent tunneling between the dots allows for the buildup of quantum coherence in the system. Under strong measurements, the coherence is suppressed, and the system is well-described by a classical model. As the measurement strength is further increased, the Zeno effect prohibits interdot tunneling. A Zeno-like effect is also observed for weak measurements, where measurement errors lead to fluctuations in the on-site energies, dephasing the system. We anticipate similar behaviors in other quantum systems under continuous measurement and feedback control, making our results relevant for implementations in quantum technology and quantum control. Published by the American Physical Society 2024
Harnessing finite-time nonadiabatic transitions that are conventionally associated with quantum inner friction for useful work extraction remains an open experimental challenge. Here we address this issue by introducing and experimentally realizing an innovative measurement-feedback quantum information engine model in the trapped 40Ca+ ion system, in which the projective measurement replaces the hot reservoir as a nonthermal energy source and the feedback control conditionally steers the system through either unitary compression-expansion strokes or thermalization. We experimentally show that the repeated feedback cycle converges to a stable operating regime with a resolved energetic balance, and, by controlling the measurement angle and stroke duration, measurement-induced coherence and the finite-time nonadiabatic contribution can enhance work extraction and raise the efficiency above the corresponding Otto benchmark. The experimental results further show that, over finite ranges of stroke durations, the efficiency and intrinsic cycle power can increase simultaneously. Our experiment establishes a route toward information-to-work quantum engines that convert finite-time irreversibility into performance-enhancing resources.
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.
Heat engines convert thermal energy into mechanical work. We here report the experimental realization of a fully quantum engine that converts quantum coherence into work. A single solid-state spin in diamond is fueled by a coherent bath and cyclically stores energy in a spin quantum battery. We establish quantum-enhanced performance by showing that almost 200%\%% more work is produced after a few cycle compared to the corresponding classical engine. We obtain concrete criteria for successful coherence-to-work conversion, and highlight the importance of a coherent motor-battery interaction. This device harnesses nonclassical features during all stages of its cycle, and demonstrates the functionality of a nanomachine whose parts are all quantum coherent.