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arxiv: 2512.13371 · v2 · submitted 2025-12-15 · 🪐 quant-ph · cond-mat.stat-mech

Impact of Information on Quantum Heat Engines

Lindsay Bassman Oftelie , Michele Campisi This is my paper

Pith reviewed 2026-05-16 22:35 UTC · model grok-4.3

classification 🪐 quant-ph cond-mat.stat-mech
keywords quantum heat enginesMaxwell's demonquantum feedback controlinformation thermodynamicstwo-stroke engineshybrid thermal machines
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The pith

Treating engine and memory as one hybrid machine with N+1 baths shows information does not always improve quantum engine performance

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper develops a general framework for two-stroke quantum heat engines that incorporate feedback control from a demon. The demon performs projective measurements on the working substance and stores the outcome in a classical memory that sits in its own thermal bath. Feedback is applied through unitary operations conditioned on the stored outcome. By regarding the working substance plus memory as a single hybrid classical-quantum system in contact with N+1 baths, the model places the engine and the information carrier on equal thermodynamic footing. This construction resolves Maxwell's paradox because entropy production in the memory bath compensates for any apparent gain from information. An explicit two-qubit example demonstrates that extracting more information can sometimes reduce efficiency and net work compared with using less information.

Core claim

The framework models a two-stroke quantum heat engine coupled to N thermal baths together with a demon whose memory is embedded in an additional bath. The demon records projective measurement outcomes and enacts conditional unitary feedback. Treating the compound working substance plus memory as a standard thermal machine interacting with N+1 baths allows ordinary thermodynamic relations to quantify how information modifies work extraction, efficiency, and power.

What carries the argument

The hybrid classical-quantum machine formed by the working substance and the demon's memory, treated as a single system in thermal contact with N+1 baths.

If this is right

  • Standard second-law bounds apply directly to the enlarged N+1 bath system.
  • Entropy production in the memory bath exactly offsets the thermodynamic benefit obtained from information.
  • In the two-qubit engine there exist parameter regimes where partial information yields higher net work than full information.
  • The framework applies to any two-stroke quantum engine that uses projective measurement and conditional unitary feedback.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Designers could deliberately limit measurement precision to reach higher performance in some quantum engines.
  • The same hybrid-bath construction could be applied to classical information engines by removing quantum coherence from the working substance.
  • If feedback steps introduce decoherence or finite-time effects, the predicted performance bounds would require correction beyond the instantaneous unitary assumption.

Load-bearing premise

The memory is embedded in its own thermal bath at a well-defined temperature and feedback operations are instantaneous unitary transformations with no back-action or decoherence.

What would settle it

An experiment measuring the total entropy production of a two-qubit engine plus memory system that finds a net negative value for the combined N+1 bath setup would contradict the framework.

Figures

Figures reproduced from arXiv: 2512.13371 by Lindsay Bassman Oftelie, Michele Campisi.

Figure 1
Figure 1. Figure 1: FIG. 1. Schematic of the physical model for a feedback-controlled [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Comparison of max-work Landauer efficiency [PITH_FULL_IMAGE:figures/full_fig_p008_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Comparison of total work output [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗
read the original abstract

The emerging field of quantum thermodynamics is beginning to reveal the intriguing role that information can play in quantum thermal engines. Information enters as a resource when considering feedback-controlled thermal machines. While both a general theory of quantum feedback control as well as specific examples of quantum feedback-controlled engines have been presented, still lacking is a general framework for such machines. Here, we present a framework for a generic, two-stroke quantum heat engine interacting with $N$ thermal baths and Maxwell's demon. The demon performs projective measurements on the engine working substance, the outcome of which is recorded in a classical memory, embedded in its own thermal bath. To perform feedback control, the demon enacts unitary operations on the working substance, conditioned on the recorded outcome. By considering the compound machine-memory as a hybrid (classical-quantum) standard thermal machine interacting with $N+1$ thermal baths, our framework puts the working substance and memory on equal footing, thereby enabling a comprehensible resolution to Maxwell's paradox and elucidating the intricate manner in which information impacts the performance of quantum engines. We illustrate the application of our framework with a two-qubit engine. A remarkable observation is that more information does not necessarily result in better thermodynamic performance: sometimes knowing less is better.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript proposes a general framework for two-stroke quantum heat engines coupled to N thermal baths and a Maxwell's demon. The demon performs projective measurements on the working substance, records outcomes in a classical memory embedded in its own thermal bath, and applies conditional unitary feedback. Treating the compound (working substance + memory) as a hybrid system interacting with N+1 baths allows standard thermodynamic relations to be applied directly, resolving Maxwell's paradox via the memory bath's entropy contribution and clarifying information's impact on performance. The framework is illustrated with a two-qubit engine, where a key observation is that more information does not necessarily improve thermodynamic efficiency or work extraction.

Significance. If the central equivalence holds, the framework provides a unified thermodynamic treatment that places the working substance and memory on equal footing, potentially enabling clearer bounds on efficiency and power in feedback-controlled quantum engines. The two-qubit example's counterintuitive result (less information sometimes being better) could stimulate further studies on optimal information use in quantum thermodynamics, provided the derivations are fully rigorous and the assumptions about instantaneous unitary operations are validated.

major comments (2)
  1. [§3] §3 (Framework derivation): The claim that the compound system behaves exactly as a standard N+1-bath thermal machine requires explicit accounting of entropy production during the projective measurement and recording steps. The manuscript must derive the total heat flows Q_i (i=1 to N+1) and show that no residual back-action or decoherence terms arise outside the memory bath; otherwise the direct application of standard bounds (e.g., Carnot-like limits) does not follow.
  2. [§4] §4 (Two-qubit illustration): The performance comparison (efficiency vs. information content) reports that 'sometimes knowing less is better,' but lacks explicit parameter values, outcome probabilities, or sensitivity to bath temperatures. The numerical results should include a table or plot showing work extraction W and efficiency η for at least three distinct measurement strengths, with a clear statement of the Hamiltonian and coupling parameters used.
minor comments (2)
  1. [Abstract] Abstract: The phrase 'a remarkable observation' should be qualified with a brief indication of the regime (e.g., 'in the weak-coupling limit') to avoid overstatement.
  2. [Notation] Notation: Ensure consistent symbols for the memory-bath heat flow (Q_{N+1}) and the information entropy term throughout; a short nomenclature table would aid readability.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading and constructive comments. We address each major comment below and have revised the manuscript to incorporate the requested clarifications and additions.

read point-by-point responses

  1. Referee: [§3] §3 (Framework derivation): The claim that the compound system behaves exactly as a standard N+1-bath thermal machine requires explicit accounting of entropy production during the projective measurement and recording steps. The manuscript must derive the total heat flows Q_i (i=1 to N+1) and show that no residual back-action or decoherence terms arise outside the memory bath; otherwise the direct application of standard bounds (e.g., Carnot-like limits) does not follow.

    Authors: We agree that a more explicit derivation strengthens the framework. In the revised manuscript we have expanded §3 with a step-by-step calculation of the heat flows Q_i (i=1…N+1). The projective measurement and classical recording are shown to contribute exclusively to the entropy change of the memory bath (bath N+1) via its heat exchange; the subsequent conditional unitary feedback is energy-conserving and introduces no additional decoherence or back-action terms outside the hybrid-system description. Consequently the compound system satisfies the standard thermodynamic relations for an N+1-bath machine without residual contributions, justifying direct application of the usual bounds. revision: yes

  2. Referee: [§4] §4 (Two-qubit illustration): The performance comparison (efficiency vs. information content) reports that 'sometimes knowing less is better,' but lacks explicit parameter values, outcome probabilities, or sensitivity to bath temperatures. The numerical results should include a table or plot showing work extraction W and efficiency η for at least three distinct measurement strengths, with a clear statement of the Hamiltonian and coupling parameters used.

    Authors: We thank the referee for this suggestion. The revised §4 now contains a table that lists the two-qubit Hamiltonian (energies and interaction strengths), the system-bath coupling parameters, the three bath temperatures, and the outcome probabilities for three measurement strengths (weak, intermediate, strong). For each case we report the extracted work W and efficiency η, confirming that weaker measurements can yield higher performance in the chosen parameter regime. A supplementary figure plotting W and η versus measurement strength has also been added. revision: yes

Circularity Check

0 steps flagged

No circularity; framework is an explicit modeling re-framing with stated assumptions

full rationale

The paper introduces its framework by directly positing that the compound machine-memory system interacts with N+1 baths as a hybrid standard thermal machine. This modeling choice is presented upfront with explicit assumptions (memory embedded in its own bath, unitary instantaneous feedback with no back-action). No equations, derivations, or self-citations are shown that reduce performance quantities or the Maxwell resolution to fitted inputs or prior self-referential results by construction. The two-qubit illustration applies the framework rather than deriving it from itself. The derivation chain is therefore self-contained against external thermodynamic bounds once the modeling assumptions are granted.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The framework rests on standard quantum mechanics (unitary evolution, projective measurements) and the assumption that the classical memory can be treated as a thermal bath at fixed temperature; no new entities are introduced.

axioms (2)
  • domain assumption Projective measurements on the working substance followed by conditional unitary feedback are valid operations in the quantum regime.
    Invoked when the demon performs measurements and enacts feedback.
  • domain assumption The classical memory can be embedded in its own thermal bath without additional back-action or decoherence costs beyond the standard thermodynamic accounting.
    Central to the hybrid machine-memory construction.

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Reference graph

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