Cooling Computers - the Quantum Physics Way
29 June 2011
"The relationship between heat, information and work is of course paramount in biology. Every mitochondria in every cell of our body is a powerhouse utilising information to convert heat of chemical reactions into useful work to maintain activity crucial for life. A really exciting prospect would be to see if there are already some existing processes in biology where quantum entanglement helps make the work extraction more efficient than allowed classically. Given that biological systems are large, warm and wet, this could only be small scale both spacially and temporally, but exciting nevertheless."
Prof Vlatko Vedral, Centre for Quantum Technologies and the University of Oxford
COOLING EFFECT: Prof Vlatko Vedral of the NUS Centre for Quantum Technologies and the University of Oxford was among the team of physicists to shed light on the thermodynamic meaning of negative entropy
Scientists have found that the deletion of data under certain conditions can create a cooling effect instead of generating heat. Prof Renato Renner of ETH Zurich Institute for Theoretical Physics and Prof Vlatko Vedral of the NUS Centre for Quantum Technologies and the University of Oxford, UK, and other physicists in their research team discovered that the cooling effect appears when the strange quantum phenomenon of entanglement is invoked. Quantum entanglement occurs when physical properties of a quantum system have become related in a single quantum state.
Their findings, which were published in the prestigious journal Nature on 1 June 2011, indicated the possibility to harness the effect to cool supercomputers that have their performance held back by heat generation.
The late physicist Rolf Landauer calculated back in 1961 that during the deletion of data, some release of energy in the form of heat is unavoidable. Landauer's 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.
Applying Landauer's principle to cases when the value of the bits to be deleted may be known, the researchers posited that it should be possible to delete the bits in such a manner that it is theoretically possible to re-create them. Taking this further, they showed that when such bits are quantum-mechanically entangled with the state of an observer, the observer could even withdraw heat from the system while deleting the bits.
Prof Renner explained that the team drew on the concepts of entropy from information theory and thermodynamics and found entropy to be a type of lack of knowledge. In measuring entropy, it should be noted that an object does not intrinsically have a certain amount of entropy; its entropy is instead always dependent on the observer.
In the case of perfect classical knowledge of a computer memory (where the observer perceives it to have zero entropy), deletion of the data requires in theory no energy at all. Hence, "more than complete knowledge" from quantum entanglement with the memory (negative entropy) leads to deletion of the data being accompanied by removal of heat from the computer and its release as usable energy.
Moving forward, the scientists' new findings relating to entropy in thermodynamics and information theory may be prove useful in other areas of research besides calculating the heat production of computers. For example, methods developed within information theory to handle entropy could lead to innovations in thermodynamics.