By University of Turku March 5, 2026
Collected at: https://scitechdaily.com/quantum-memory-isnt-what-we-thought-physicists-reveal-a-hidden-duality/
Quantum systems may hide memory in unexpected ways.
An international team of scientists has taken a closer look at how memory functions in quantum systems and their time evolution. Their study reveals that whether a quantum process appears to have memory depends on how it is examined. From one angle, the process may seem completely memoryless. From another, traces of past behavior remain visible. The findings open new paths for research in quantum science and emerging technologies.
In classical physics, memory is defined in a straightforward way. If a system’s future behavior depends only on its current condition, it is considered memoryless. If earlier states continue to influence what happens next, the system is said to have memory.
Quantum physics complicates this picture. Quantum systems can store and transmit information in ways that have no counterpart in classical science. In addition, measurement is not just a passive observation. It plays an active and fundamental role in how quantum systems evolve.
Rethinking Memory in Quantum Mechanics
In a study published in PRX Quantum, researchers from the University of Turku in Finland, the University of Milan in Italy, and Nicolaus Copernicus University in Toruń in Poland revisited the meaning of “memory” in the quantum world.
“Our work shows that memory is not a single concept but can manifest in different ways depending on how the evolution of a system is described,” says first author, Doctoral Researcher Federico Settimo from the University of Turku.
Two Perspectives, Different Memory Signatures
For years, scientists have analyzed memory effects by focusing on how quantum states change over time. This framework, first introduced by Erwin Schrödinger, treats the state of a system as the central object that evolves.
Quantum theory, however, also provides another equally fundamental viewpoint developed by Werner Heisenberg. Instead of tracking how states change, this approach examines how observables evolve. Observables are the measurable physical quantities recorded in experiments.
Although both approaches produce identical predictions for experimental outcomes, the new research shows that they do not describe memory in the same way.
The team found that this distinction directly affects how memory can be identified. Certain memory effects become visible only when studying the evolution of quantum states. Others appear only when focusing on the behavior of observables.
As a result, the same quantum process can look memoryless under one description and memory-dependent under another. This discovery suggests that quantum memory is more complex than previously recognized and cannot be fully understood by examining quantum states alone.
Implications for Quantum Technologies
“Our findings open up new research avenues into the dynamics of quantum systems. Moreover, our work has implications beyond its foundational significance for quantum technologies, where the external environment induces noise and memory effects. Knowing how memory can be witnessed is essential for developing strategies to mitigate noise or exploit environmental effects in realistic quantum devices,” says Professor of Theoretical Physics Jyrki Piilo from the University of Turku.
In practical terms, quantum devices constantly interact with their surroundings, which introduces noise and can generate memory effects. A clearer understanding of how to detect and interpret these effects could help researchers reduce unwanted interference or even use environmental interactions to improve performance.
Overall, the study sheds light on a core feature of quantum dynamics and shows how the uniquely quantum character of time evolution reshapes even basic ideas such as memory.
Reference: “Divisibility of Dynamical Maps: Schrödinger Versus Heisenberg Picture” by Federico Settimo, Andrea Smirne, Kimmo Luoma, Bassano Vacchini, Jyrki Piilo and Dariusz Chruściński, 26 February 2026, PRX Quantum.
DOI: 10.1103/6dt2-sq44
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