Quantum systems can remember and forget at the same time, scientists discover

A quantum system can simultaneously appear to have forgotten its past and retained it, depending on the observer's chosen lens, a new study reveals. | Contesto: cronaca

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• Quantum systems can remember and forget at the same time, scientists discover

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A team of scientists has discovered that quantum systems can harbor a hidden memory of their past, even when they appear to have none. The research, published this week, reveals a fundamental duality in how memory is defined and observed at the quantum scale. Whether a system is judged to "remember" depends entirely on the perspective of the observer: one looking at the system's internal quantum state, or another focused solely on the measurable properties it outputs. This finding challenges classical intuitions and suggests that memory in the quantum realm is not an absolute property but a relational one, contingent on the question being asked. The core of the discovery lies in the distinction between two frameworks for analyzing a system's evolution. When scientists track the complete quantum state—the full, probabilistic description of a system—they can detect a form of memory known as non-Markovianity. This indicates the system's future behavior is influenced by its past in a complex, non-linear way. However, when the analysis is restricted to the system's observable outputs, the very same process can appear Markovian, meaning it seems to have no memory at all, with each step determined only by the immediate present. The breakthrough is the realization that both descriptions can be simultaneously true for a single quantum process. This paradoxical behavior, where a system can be memoryless and memory-filled at once, stems from the unique nature of quantum information. The internal quantum state contains information that is not fully accessible through standard measurements. What an experimenter can see—the observables—provides only a partial window into the system's history. Consequently, from the narrow viewpoint of those outputs, the past seems irrelevant, while the richer, hidden state narrative retains a coherent thread of history. It is a stark demonstration of quantum contextuality, where the answer to a question like "does this have memory?" is not fixed but depends on the specific investigative protocol. The implications for emerging quantum technologies are profound. Quantum computers, sensors, and communication networks are all built on the...

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Categoria: cronaca