An international team of scientists has delved into how memory works in quantum systems and uncovered surprising results. Their research shows that even though quantum processes appear completely memoryless from one perspective, they still retain memory when examined from another perspective. This unexpected discovery opens the door to a new field of research in quantum science and technology.
In classical physics, the concept of memory is simple. A system is considered memoryless if its future behavior depends only on its current state. A system is said to have memory if its past state continues to influence what happens next.
Quantum physics is not so clear-cut. Quantum systems can store and transfer information in ways that their classical counterparts cannot, and the measurements themselves play a key role in how these systems evolve. For this reason, defining memory in terms of quantum mechanics remains a challenge.
Rethinking memory in quantum systems
In a study published in PRX Quantumresearchers from the University of Turku in Finland, the University of Milan in Italy, and Nicolaus Copernicus University in Toruń, Poland, revisited the concept of memory in quantum systems to better understand its implications.
“Our study shows that memory is not a single concept and can manifest in different ways depending on how the evolution of the system is described,” said first author Federico Settimo, a postdoctoral researcher at the University of Turku.
Two perspectives on quantum mechanics
Scientists have long studied memory by tracking how quantum states change over time. This approach is rooted in the work of Erwin Schrödinger. However, quantum theory also provides another equally important framework, developed by Werner Heisenberg. Rather than focusing on states, this perspective looks at how observable quantities evolve, i.e., measurable properties seen in experiments.
Although both approaches yield the same experimental results, new research shows that they are not compatible when it comes to explaining memory.
Hidden memory effect revealed
The researchers found that these two perspectives can reveal different types of memories. Some memory effects only appear when you analyze the evolution of quantum states, while other effects are only visible when you focus on what is observable.
This means that a quantum system may appear to have no memory in one description, but show clear signs of memory in another. This discovery suggests that quantum memory is more complex than previously thought and cannot be fully understood by observing quantum states alone.
Impact on quantum technology
“Our findings open new research avenues into the dynamics of quantum systems. Moreover, our work has implications beyond its fundamental importance for quantum technologies, where the external environment induces noise and memory effects. Knowing how memory is witnessed is essential for developing strategies to reduce noise or exploit environmental effects in realistic quantum devices,” said Jyrki Piilo, Professor of Theoretical Physics at the University of Turku. says.
This research sheds new light on fundamental aspects of quantum mechanics by revealing how memory works in quantum systems. It also highlights how the unique nature of quantum time evolution is reshaping even fundamental concepts such as memory, with potential implications for future technologies.
