Quantum knowledge may cool computers

June 1, 2011

Researchers at ETH Zurich/Swiss Federal Institute of Technology and colleagues have found that the deletion of data, under certain conditions, can create a cooling effect instead of generating heat.

The physicist Rolf Landauer calculated in 1961 that during the deletion of data, some release of energy in the form of heat is unavoidable. The new study revisits 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 recreate them. Such reversible deletion would generate no heat, the researchers said.

However, the researchers showed 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.

The data can only be deleted once, so there is no possibility to continue to generate energy, the researchers said. The process also destroys the entanglement, and it would take an input of energy to reset the system to its starting state. The equations are consistent with the second law of thermodynamics: the entropy of the universe can never decrease.

“We’re working on the edge of the second law,” says physicist Vlatko Vedral. “If you go any further, you will break it.”

Lídia del Rio, Johan Aberg, et al., The thermodynamic meaning of negative entropy, Nature, 2011; 474 (7349): 61 [DOI:10.1038/nature10123]