Coherent states 6.1 | Quantum coherence, 6.1

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

In laser, all photons are in-phase with each other.

In other electromagnetic waves, the photons are out of phase. However, they still have constant phase difference (aka coherence), unless the photons are emitted by thermal radiation (thermal light). 

— Me@2011.10.06

However, such a picture is incorrect.

— Me@2011.10.12

In classical optics light is thought of as electromagnetic waves radiating from a source. Often, coherent laser light is thought of as light that is emitted by many such sources that are in phase. Actually, the picture of one photon being in-phase with another is not valid in quantum theory.

— Wikipedia on Coherent states

2011.10.12 Wednesday (c) All rights reserved by ACHK

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

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

2011.10.09 Sunday ACHK

Coherent states 3

In classical optics light is thought of as electromagnetic waves radiating from a source. Often, coherent laser light is thought of as light that is emitted by many such sources that are in phase. Actually, the picture of one photon being in-phase with another is not valid in quantum theory.

Laser radiation is produced in a resonant cavity where the resonant frequency of the cavity is the same as the frequency associated with the atomic transitions providing energy flow into the field. As energy in the resonant mode builds up, the probability for stimulated emission, in that mode only, increases. That is a positive feedback loop in which the amplitude in the resonant mode increases exponentially until some non-linear effects limit it.

As a counter-example, a light bulb radiates light into a continuum of modes, and there is nothing that selects any one mode over the other. The emission process is highly random in space and time (see thermal light). In a laser, however, light is emitted into a resonant mode, and that mode is highly coherent. Thus, laser light is idealized as a coherent state.

— Wikipedia on Coherent states

2011.10.07 Friday ACHK

Quantum coherence, 4

O’Connell and his colleagues coupled together a mechanical resonator, similar to a tiny springboard, and a qubit, a device that can be in a superposition of two quantum states at the same time. They were able to make the resonator vibrate a small amount and a large amount simultaneously — an effect which would be impossible in classical physics. The mechanical resonator was just large enough to see with the naked eye — about as long as the width of a human hair.

— Wikipedia on Quantum machine

2011.10.04 Tuesday ACHK

Large-scale (macroscopic) quantum coherence leads to novel phenomena. For instance, the laser, superconductivity, and superfluidity are examples of highly coherent quantum systems, whose effects are evident at the macroscopic scale. These examples of quantum coherence are Bose–Einstein condensates. Here, all the particles that make up the condensate are in-phase; they are thus necessarily all described by a single quantum wavefunction.

On the other hand, the Schrodinger’s cat thought experiment, highlights the fact that quantum coherence is not typically seen at the macroscopic scale but has been observed in the motion of a mechanical resonator (see Quantum machine).

— Wikipedia on Quantum coherence

2011.10.02 Sunday ACHK

Quantum coherence

The quantum description of perfectly coherent paths is called a pure state, in which the two paths are combined in a superposition. The correlation between the two particles exceeds what would be predicted for classical correlation alone (see Bell’s inequalities).

— Wikipedia on Quantum coherence

2011.09.30 Friday ACHK

The broad notion is that “mass there influences inertia here”.

— Wikipedia on Mach principle

Mach principle states that the inertial mass of an object is due to (the gravitational influences of) other objects.

In other words, the inertial mass of an object is due to the gravitational mass of itself and the gravitational masses of other objects.

— Me@2011.09.24

2011.09.27 Tuesday (c) All rights reserved by ACHK

“A purpose of life” is to locally decrease the entropy

which is pretty unusual among the natural phenomena.

— Ten new things modern physics has learned about time

— Lubos Motl

2011.09.25 Sunday ACHK

AdS/CFT correspondence 4

AdS/CFT is a unification of field theory and string theory – a kind of spectacular meta-unification, too.

— Unification as a source of certainty

— Lubos Motl

2011.09.24 Saturday ACHK

In fact, all the dualities in string theory are obviously examples of unification. The electric charge is unified with the momentum of a particle; this insight was already known to Kaluza or at least Klein. That’s true because the electric charge is the generator of an isometry in a new 5th circular dimension – which is the momentum in this direction.

— Unification as a source of certainty

— Lubos Motl

2011.09.22 Thursday ACHK