Sunday 18 May 2025
A new framework for understanding macroscopic states in quantum systems has been developed, offering a unified perspective on irreversibility and retrodiction in quantum mechanics. The research builds upon the concept of observational entropy, which measures how much information is lost when observing a quantum system.
The team’s approach defines macroscopic states as fixed points of a coarse-graining map, essentially a measurement process that reduces the complexity of a quantum state. This definition provides several equivalent characterizations of macroscopic states, including conditions based on statistical sufficiency and the structure of maximal projective post-processings.
One key implication of this framework is that it generalizes existing resource theories of coherence, athermality, purity, and asymmetry. These theories describe how different types of quantum information can be used to perform specific tasks, such as correcting errors in quantum computers or manipulating the properties of particles.
The researchers’ approach also provides a new perspective on the concept of retrodiction, which is the process of inferring the past state of a system based on its current measurement outcomes. By defining macroscopic states as fixed points of a coarse-graining map, the team has shown that retrodiction can be understood as a form of inference about the past state of a system.
The framework also offers insights into the nature of entropy production in quantum systems. Entropy is a measure of the disorder or randomness of a system, and its production is closely tied to the second law of thermodynamics, which states that entropy always increases over time.
In this context, the researchers’ findings suggest that entropy production can be understood as a process that occurs at the level of individual measurements, rather than being a property of the system as a whole. This perspective offers new opportunities for understanding and manipulating entropy production in quantum systems, potentially leading to advances in fields such as quantum computing and quantum thermodynamics.
The team’s work has significant implications for our understanding of the fundamental principles of quantum mechanics. By providing a unified framework for macroscopic states and retrodiction, it offers a deeper understanding of how quantum systems behave at scales that are relevant to everyday life.
The research also highlights the importance of considering the role of measurement in shaping our understanding of quantum systems. By recognizing that measurement is an essential part of the process of inferring the properties of a system, we can gain new insights into the nature of reality itself.
Overall, this breakthrough has significant implications for our understanding of the quantum world and its applications to technology and science.
Cite this article: “Quantum Macrostates: A Framework for Understanding Irreversibility and Retrodiction in Quantum Mechanics”, The Science Archive, 2025.
Quantum Mechanics, Macroscopic States, Observational Entropy, Retrodiction, Coarse-Graining Map, Quantum Information, Resource Theories, Coherence, Thermodynamics, Entropy Production
