Daily Archives: October 13, 2011

Laser 2.2

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Coherent states 6.2 | Quantum coherence, 6.2

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

A laser is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emission of photons. The emitted laser light is notable for its high degree of spatial and temporal coherence, unattainable using other technologies.

Temporal (or longitudinal) coherence implies a polarized wave at a single frequency whose phase is correlated over a relatively large distance (the coherence length) along the beam. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase which vary randomly with respect to time and position, and thus a very short coherence length.

— Wikipedia on Laser

The amplitude of the EM wave does not have an a-priori well-defined value. The photon number must follow a Poisson distribution. The coherent states provide the most well-defined magnitude and phase. They come closest to the classical notion of a wave.

— Dr. Michael A. Parker

The amount of quantum noise in the electric field is completely independent of the phase. As the field strength, i.e. the oscillation amplitude α of the coherent state is increased, the quantum noise or uncertainty is constant at 1/2, and so becomes less and less significant. In the limit of large field the state becomes a good approximation of a noiseless stable classical wave.

— Wikipedia on Coherent states

Classical electromagnetic wave can be regarded as coherent states of photons, not because the photons are coherent with each other, which is not well-defined, but because each photon is in a coherent state, which evolves around the classical trajectory, providing a near definite classical electromagnetic wave amplitude.

— Me@2011.10.12

2011.10.13 Thursday (c) All rights reserved by ACHK

Writer’s block 2

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缺乏寫作靈感 2

[At a seminar, Charlie Kaufman has asked McKee for advice on his new screenplay in which ‘nothing much happens’.]
   
Robert McKee: Nothing happens in the world? Are you out of your mind? People are murdered every day. There’s genocide, war, corruption. Every day, somewhere in the world, somebody sacrifices his life to save someone else. Every day, someone, somewhere makes a conscious decision to destroy someone else. People find love, people lose it. For Christ’s sake, a child watches her mother beaten to death on the steps of a church. Someone goes hungry. Somebody else betrays his best friend for a woman. If you can’t find that stuff in life, then you, my friend, don’t know crap about life. And why are you wasting my two precious hours with your movie? I don’t have any use for it. I don’t have any bloody use for it.
   
Charlie Kaufman: Ok, thank you.
   

— Adaptation.

— Charlie Kaufman

2011.10.13 Thursday ACHK

Curiosity 2

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I’d always supposed that all smart people were curious — that curiosity was simply the first derivative of knowledge.

— Paul Graham

你智力的高低，取決於你知識的多少。

你知識增長的快慢，取決於你好奇心的大小。

— Me@2011.10.12

2011.10.12 Wednesday (c) All rights reserved by ACHK