Editor's Summary
10 April 2008
Extreme measurements
Erez et al. enter uncharted territory with their prediction of the behaviour of a hitherto unexplored quantum mechanical setting in which neither the second law of thermodynamics, nor the common notion that heat always flows from hotter to colder ensembles, can be relied upon. In work compared in the accompanying News and Views piece to a quantum evocation of Maxwell's demon, the processes of quantum measurement appear to control thermodynamical behaviour. The system considered consists of two energy levels surrounded by a 'heat bath' that can supply or soak up any amount of heat. In such two-level quantum systems, the act of making a measurement can cause their relaxation to either slow down (the Zeno effect, where a continuously observed unstable particle never decays), or to speed up (the anti-Zeno effect). The latter effect is associated with a decrease in entropy and temperature of the system and its bath, while the former results in heating and higher entropy. That type of behaviour breaks the standard thermodynamical rules. In practical terms, these anomalies may offer the possibility of very fast control of heat and entropy in quantum systems.
News and Views: Quantum physics: Observations turn up the heat
The idea that observers can influence what they observe has a history that stretches back beyond quantum physics. That we can affect how a system heats up and cools down simply by probing it is a new twist.
Kimberly R. Chapin & Marlan O. Scully
doi:10.1038/452705a
Letter: Thermodynamic control by frequent quantum measurements
Noam Erez, Goren Gordon, Mathias Nest & Gershon Kurizki
doi:10.1038/nature06873
First paragraph | Full Text | PDF (385K) | Supplementary information