Measuring the Cost of Forgetting in Quantum Systems
In a collaborative study by TU Wien and FU Berlin, scientists have successfully measured the effects of information loss in quantum systems, shedding new light on the deep ties between thermodynamics, information theory, and quantum physics.
At first glance, heat and information appear unrelated—heat is central to thermodynamics, while information theory belongs to the realm of abstract mathematics. However, in the 1960s, physicist Rolf Landauer revealed a fundamental connection: deleting information is unavoidably linked to energy exchange. Any act of erasing data results in the release of heat, making the process energetically costly.
This concept, known as Landauer’s principle, has become increasingly important in quantum theory. Researchers at TU Wien have now demonstrated this principle in many-particle quantum systems and measured it quantitatively for the first time. The study, published in Nature Physics, confirms that when a quantum system loses or "forgets" information, it involves an exchange of entropy and energy with the environment.
According to Professor Jörg Schmiedmayer of TU Wien's Atomic Institute, the deletion of information always incurs an energetic price. Regardless of the method used, erasing even a single bit of data results in an increase in entropy, implying energy dissipation. This limitation is critical for quantum computing and the development of efficient information processing technologies.
But what does it physically mean to forget or erase information? In classical physics, systems like planetary orbits are deterministic—knowing their current state allows for precise predictions about the past and future, indicating that no information has been lost. The information remains encoded in the system's present state and is, at least in principle, recoverable.
Quantum systems, however, behave differently. While their evolution can be reversible in isolation, once they interact with their environment—such as during measurement—their states are altered irreversibly. Information leaks into the surroundings in a process that cannot be undone.
The researchers studied this phenomenon using ultracold clouds of rubidium atoms held in place by an atom chip. After cooling thousands of atoms and releasing two separate atom clouds to overlap, the system was split conceptually: one part was analyzed as the quantum system, while the remainder acted as the environment. By observing the interaction between these two components, the researchers were able to track how information gradually escaped from the system, confirming the fundamental thermodynamic cost of quantum information loss.
This research deepens our understanding of how information behaves in quantum systems and lays groundwork for future advances in quantum computing, where managing the flow and loss of information is a central challenge.
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