Decoherence is the effect that causes a quantum system to behave classically. The most known of this kind of effects is due to environment where the interaction of an open quantum system with its surrounding is the reason for the loss of quantum coherence. This effect is well-proven on an experimental ground and must be considered acquired knowledge. On the other side, it is a correct scientific question to ask if a closed quantum system ever displays classical behavior for some reason. I have already put forward my take in this blog (see here). This week, on Physical Review Letters (see here and here), it is appeared a paper showing how intrinsic decoherence comes out in an experimental setup of two coupled kicked rotors. Kicked rotors are the epitome of studies on classical chaos and corresponding quantum behavior. It is known that, classically, such a system display diffusion above a certain threshold, firstly computed by Boris Chirikov. The corresponding quantum system localizes instead when its classical counterpart is chaotic. This is the hallmark of a proper quantum behavior that refrains from chaos proper to classical nonlinear systems. The main reason is that the Schrödinger equation is just linear and superposition principle applies. On 1988, S. Adachi, M. Toda, and K. Ikeda showed a real beautiful result that two of such coupled systems lose quantum coherence (see here). The paper by Bryce Gadway, Jeremy Reeves, Ludwig Krinner, and Dominik Schneble (see here) is an experimental proof of the fact that the original theoretical result is a correct insight and we have again a proof that environmental decoherence is not all the story. An interesting recount is given here. This paper is really striking and open the door to a new class of experiments where closed quantum systems, possibly with a lot of systems involved, will be studied to give a full understanding of the quantum-classical transition.

Bryce Gadway, Jeremy Reeves, Ludwig Krinner, & Dominik Schneble (2012). Evidence for a Quantum-to-Classical Transition in a Pair of Coupled

Quantum Rotors Phys. Rev. Lett. 110, 190401 (2013) arXiv: 1203.3177v2

Adachi, S., Toda, M., & Ikeda, K. (1988). Quantum-Classical Correspondence in Many-Dimensional Quantum Chaos Physical Review Letters, 61 (6), 659-661 DOI: 10.1103/PhysRevLett.61.659