Comparison of various types of coherence and emergent coherent systems

Abstract

Coherence is a collective property that is present in Bose-Einstein condensates (BEC), an example of which when charged is superconductivity (SC). Coherence is also believed to be present to a degree in highly efficient energy transfer in certain biological systems. Attributes of coherent systems are examined in BEC, superfluidity and Bardeen, Cooper, and Schrieffer SC and a laser in part 1. Part 2 consists of examination of various proposals for coherence including "emergent coherent systems" where there may be coherence but no phase transition. We discuss "cold" atomic gases, the Casimir effect, an extended version of Förster's resonance energy transfer, Fröhlich's model, exciton-coupled quantum wells, and conceptually "old" polaritons rejuvenated by new developments. A discussion about highly efficient energy transfer in photosynthesis along with our proposal for a possible new model for this system is the last of the examples. We finish with a discussion about emergent coherent systems and attempt to classify the examples of parts 1 and 2. © 2013 Wiley Periodicals, Inc. Coherence in molecular systems has evolved considerably since the fundamental insights of London and Penrose and Onsager and the first "cold atom" studies of the 1990s. This article provides a comprehensive review of the most important examples of coherent systems, from Bose-Einstein condensates, to superfluidity, to "cold" atomic gases. The role of coherence in the highly efficient energy transfer in photosynthesis and possible new models for it are also discussed. Copyright © 2013 Wiley Periodicals, Inc.