Quantum physics behind computer temperature
Have you ever thought about the physics behind the familiar whirring of a laptop as it overheats while sitting on your knee? Or the overwhelming heat generated by an office full of active computers or a server room? Now an international team of theoretical physicists has made the extraordinary discovery that as well as producing heat, computers can conversely also have a cooling effect. Writing in the journal Nature, the team from the United Kingdom, Switzerland and Singapore build on the well-established fact that the energy consumed by 'active' computers will eventually end up as heat. Their study, which received a funding boost from the European Research Council, reveals how under certain conditions the deletion of data can instead create a cooling effect. These findings could have implications for our ability to manually cool so called 'supercomputers', whose performance is often held back by overheating. Supercomputers are used for tasks that require a high level of processing capacity, such as for meteorology or molecular modelling. The scientists explain that this cooling effect is as a result of the quantum phenomenon of entanglement. 'Achieving the control at the quantum level that would be required to implement this in supercomputers is a huge technological challenge, but it may not be impossible. We have seen enormous progress in quantum technologies over the past 20 years,' explains Vlatko Vedral, one of the study's authors. 'With the technology in quantum physics labs today, it should be possible to do a proof of principle experiment on a few bits of data.' It was the physicist Rolf Landauer who first worked out in 1961 that when data is deleted it is inevitable that energy will be released in the form of heat. This principle implies that when a certain number of arithmetical operations per second have been exceeded, the computer will produce so much heat that the heat is impossible to dissipate. Although for supercomputers today other sources of heat are more important, the team believes that the critical threshold where Landauer's erasure heat becomes important may be reached within the next 10 to 20 years. The heat emission from the deletion of a 10 terabyte hard drive amounts to little over less than a millionth of a joule. However, if such a deletion process were repeated many times per second then the heat would accumulate correspondingly. This new study puts the spotlight back on Landauer's principle for cases when the values of the bits to be deleted may be known. When the memory content is known, it should be possible to delete the bits in such a manner that it is theoretically possible to re-create them. Previous studies have shown that such reversible deletion would generate no heat. This new study moves things forward by showing that when the bits to be deleted are quantum-mechanically entangled with the state of an observer, then the observer could even withdraw heat from the system while deleting the bits. Entanglement links the observer's state to that of the computer in such a way that they know more about the memory than is possible in classical physics. In their study, the team used ideas from information theory and thermodynamics in a concept known as entropy. In information theory, entropy is a measurement of the information density that describes how much memory capacity a given set of data would take up when compressed optimally. However, in thermodynamics, entropy relates to the disorder in systems, for example to the arrangement of molecules in a gas. In thermodynamics, adding entropy to a system is usually equivalent to adding energy as heat. 'We have now shown that in both cases, the term entropy is actually describing the same thing even in the quantum mechanical regime. Our study shows that in both cases, entropy is considered to be a type of lack of knowledge,' says Renato Renner, from the research team. In practice, these findings mean that if two individuals delete data in a memory and one has more knowledge of this data, the memory is perceived to have lower entropy and can be deleted using less energy. As well as being useful for our knowledge of the heat production of computers, this study could have positive implications for the development of innovations in thermodynamics.For more information, please visit:ETH Zürich:http://www.ethz.ch/index_EN
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Switzerland, Singapore, United Kingdom