Daily Archives: October 10, 2011

Coherent states 5

Posted on by

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

Freeman Dyson

Posted on by

Certainly the growing rigidity of scientific organizations is a real and serious problem. I like to remind young scientists of examples in the recent past when people without paper qualifications made great contributions. Two of my favorites are: Milton Humason, who drove mules carrying material up the mountain trail to build the Mount Wilson Observatory, and then when the observatory was built got a job as a janitor, and ended up as a staff astronomer second-in-command to Hubble. Bernhardt Schmidt, the inventor of the Schmidt telescope which revolutionized optical astronomy, who worked independently as a lens-grinder and beat the big optical companies at their own game. I tell young people that the new technologies of computing, telecommunication, optical detection and microchemistry actually empower the amateur to do things that only professionals could do before.

Amateurs and small companies will have a growing role in the future of science. This will compensate for the increasing bureaucratization of the big organizations. Bright young people will start their own companies and do their own science.

— Freeman Dyson

2011.10.10 Monday ACHK

辛亥革命一百週年