Quantum coherence, 5

Every-day electromagnetic radiation, such as radio and TV waves, is also an example of near coherent states (macroscopic quantum coherence). That should “give one pause” regarding the conventional demarcation between quantum and classical.

— Wikipedia on Coherent states

classical electromagnetic radiation (coherent states)  

versus

laser (macroscopic quantum coherence)

Coherent states and quantum coherence are two different concepts, not directly related to each other.

Coherent states is a kind of states of a particle or a system. It is about the evolution of the wavefunction of a single particle or a system.

Quantum coherence is another concept. It is about pure state: all the particles in the system are in the same pure quantum state. The particles in that system have definite phase relationships. A special case is that all the particles in a system are in-phase. Then the whole system can be represented by a single quantum wavefunction. Such phenomenon is called macroscopic quantum coherence.

Although coherent states and quantum coherence are not directly related, they are indirectly related. If most of the particles in a system are in their own coherent states, which means that each evolves with minimum uncertainty, they are more likely to be quantumly coherent with each other.

— Me@2011.10.06

— Me@2011.10.10

2011.10.10 Monday (c) All rights reserved by ACHK