Abstract The so-called information-thermodynamics link created by a thought experiment of Szilard became a core of modern orthodoxy in the field of quantum information and resources theory in quantum thermodynamics. We recall existing objections against standard interpretation of Szilard engine operation and illustrate them by two quantum models: a particle in a box with time-dependent thin potential barrier and the spin-boson model. The consequences of the emerging superselection rules for thermodynamics and foundations of quantum mechanics are discussed. The role of non-ergodic systems as information carriers and the thermodynamic cost of stability and accuracy of information processing is briefly discussed and compared to the generally accepted Landauer’s principle.
Abstract The so-called information-thermodynamics link created by a thought experiment of Szilard became a core of modern orthodoxy in the field of quantum information and resources theory in quantum thermodynamics. We recall existing objections against standard interpretation of Szilard engine operation and illustrate them by two quantum models: a particle in a box with time-dependent thin potential barrier and the spin-boson model. The consequences of the emerging superselection rules for thermodynamics and foundations of quantum mechanics are discussed. The role of non-ergodic systems as information carriers and the thermodynamic cost of stability and accuracy of information processing is briefly discussed and compared to the generally accepted Landauer’s principle.
The Szilárd engine is a mechanism (akin to Maxwell's demon) for converting information into energy, which seemingly violates the second law of thermodynamics. Originally a classical thought experiment, it was extended to a quantized treatment by Zurek. Here, we examine a new, elegant model of a quantum Szilárd engine by replacing the traditional rigid box with a harmonic potential, extending the scope of the model. Remarkably, almost all calculations are exact. This article is suitable for students, researchers, and educators interested in the conceptual links among information, entropy, and quantum measurement.
In a classic thought experiment, Szilard suggested a heat engine where a single particle, for example an atom or a molecule, is confined in a container coupled to a single heat bath. The container can be separated into two parts by a moveable wall acting as a piston. In a single cycle of the engine, work can be extracted from the information on which side of the piston the particle resides. The work output is consistent with Landauers principle that the erasure of one bit of information costs the entropy kB ln 2, exemplifying the fundamental relation between work, heat and information. Here we apply the concept of the Szilard engine to a fully interacting quantum many-body system. We find that a working medium of a number of bosons (larger or equal two) with attractive interactions is clearly superior to other previously discussed setups. In sharp contrast to the classical case, we find that the average work output increases with the particle number. The highest overshoot occurs for a small but finite temperature, showing an intricate interplay between thermal and quantum effects. We anticipate that our finding will shed new light on the role of information in controlling thermodynamic fluctuations in the deep quantum regime, which are strongly influenced by quantum correlations in interacting systems.
We analyze an engine whose working fluid consists of a single quantum particle, paralleling Szilard's construction of a classical single-particle engine. Following his resolution of Maxwell's Second Law paradox using the latter, which turned on physically instantiating the demon (control subsystem), the quantum engine's design mirrors the classically-chaotic Szilard Map that operates a thermodynamic cycle of measurement, thermal-energy extraction, and memory reset. Focusing on the thermodynamic costs to observe and control the particle and comparing these in the quantum and classical limits, we detail the thermodynamic tradeoffs behind Landauer's Principle for information-processing-induced thermodynamic dissipation in the quantum and classical regimes. In particular, and as found with the classical engine, we show that the sum of the thermodynamic costs over a cycle obeys a generalized Landauer Principle, exactly balancing energy extraction from the heat bath. Thus, the quantum engine obeys the Second Law. However, the quantum engine does so via substantially different mechanisms: classically measurement and erasure determine the thermodynamics, while in the quantum implementation the cost of partition insertion is key.
We look at certain thought experiments based upon the 'delayed choice' and 'quantum eraser' interference experiments, which present a complementarity between information gathered from a quantum measurement and interference effects. It has been argued that these experiments show the Bohm interpretation of quantum theory is untenable. We demonstrate that these experiments depend critically upon the assumption that a quantum optics device can operate as a measuring device, and show that, in the context of these experiments, it cannot be consistently understood in this way. By contrast, we then show how the notion of 'active information' in the Bohm interpretation provides a coherent explanation of the phenomena shown in these experiments. We then examine the relationship between information and entropy. The thought experiment connecting these two quantities is the Szilard Engine version of Maxwell's Demon, and it has been suggested that quantum measurement plays a key role in this. We provide the first complete description of the operation of the Szilard Engine as a quantum system. This enables us to demonstrate that the role of quantum measurement suggested is incorrect, and further, that the use of information theory to resolve Szilard's paradox is both unnecessary and insufficient. Finally we show that, if the concept of 'active information' is extended to cover thermal density matrices, then many of the conceptual problems raised by this paradox appear to be resolved.
The Szilard engine is a foundational thought experiment that rigorously links thermodynamicsand information theory. With the miniaturization of devices and ongoingprogress in quantum information science, it is crucial to examine how quantumeffects influence the operation of such engines. This thesis investigates the finitetimedynamics of a quantum Szilard engine subjected to size-invariant shape transformations,in which the geometry of the confinement potential is deformed withoutaltering its overall size. The system’s evolution is modeled using a time-dependent,Markovian LGKS (Lindblad-Gorini-Kossakowski-Sudarshan) master equation. Wenumerically solve this equation to analyze the thermodynamic behavior of the engine,focusing on the roles of quantum coherence and its interplay with heat, work,and entropy throughout the cycle. Special attention is given to how coherenceevolves under varying barrier insertion rates and thermalization temperatures. Wedemonstrate that coherence generation is strongly influenced by both the protocolspeed and the bath temperature. Furthermore, we show a connection between coherenceaccumulation and the energetic and informational cost of the cycle. Thesefindings enhance our understanding of coherence in finite-time, measurement-basedquantum devices and suggest that geometric deformations can serve as a powerfultool for thermodynamic control in quantum technologies.
It is often claimed, that from a quantum system of d levels, and entropy S and heat bath of temperature T one can draw kT lnd–TS amount of work. However, the usual arguments basing on Szilard engine, are not fully rigorous. Here we prove the formula within Hamiltonian description of drawing work from a quantum system and a heat bath, at the cost of entropy of the system. We base on the derivation of thermodynamical laws and quantities in [10] within weak coupling limit. Our result provides fully physical scenario for extracting thermodynamical work form quantum correlations [4]. We also derive Landauer's principle as a consequence of the second law within the considered model.