Which properties of the quantum are random?

[San K]

Which properties of the photon/quantum are random?

Spin - Yes
Position (within the "range/orbital") - Yes
Momentum - Yes

Phase - No
Polarization - No
Coherence (derivative of phase) - No

Is the above correct? Please add the properties I missed

 

[Demystifier]

Polarization of a photon is essentially the same as as spin of a photon. In that sense, polarization is also "random", i.e. subject to probabilistic laws.

Phase of a single photon is not even measurable.

 

[San K]

Polarization of a photon is essentially the same as as spin of a photon. In that sense, polarization is also "random", i.e. subject to probabilistic laws.

Phase of a single photon is not even measurable.

interesting...then why do we have left and right polarizers?

i mean the left polarizer would allow only left-photons to pass through...but if polarization is random then the left polarizers would keep changing?

 

[Demystifier]

interesting...then why do we have left and right polarizers?

i mean the left polarizer would allow only left-photons to pass through...but if polarization is random then the left polarizers would keep changing?

But you can also have a photon in the vertical (or horizontal) polarization, which is a superposition of left and right polarization. If you transmit such a photon through a left polarizer, there is a 50% chance that it will pass. So, it's probabilistic too.

 

[Zarqon]

Just a point: You can't really say that a specific property is always random or not, it depends on the context, and how you have prepare a particular state. For example, a photon in a Fock state has a known photon number, but an unknown (random) phase, whereas a photon prepared in a coherent state may have a well known phase, but instead containing an unknown (random) number of photons.

 

[San K]

Just a point: You can't really say that a specific property is always random or not, it depends on the context, and how you have prepare a particular state. For example, a photon in a Fock state has a known photon number, but an unknown (random) phase, whereas a photon prepared in a coherent state may have a well known phase, but instead containing an unknown (random) number of photons.

interesting. so the same property can be random/non-random depending upon the state?

i.e. can we lock/unlock the randomness, in properties, of a photon?

 

[Goldstone1]

interesting. so the same property can be random/non-random depending upon the state?

i.e. can we lock/unlock the randomness, in properties, of a photon?

Sure, all you need to know is all the eigenstates of a particles. But knowing two complimentary observables however, makes it an issue that ''randomness'' is a word which replaces a ''lack of knowledge'' on the system. Randomness is an illusion of our semantic attachment for the need to know everything.

 

[San K]

Sure, all you need to know is all the eigenstates of a particles. But knowing two complimentary observables however, makes it an issue that ''randomness'' is a word which replaces a ''lack of knowledge'' on the system. Randomness is an illusion of our semantic attachment for the need to know everything.

I had similar ideas, subject to verification.

But knowing two complimentary observables

how? can you give an example/experiment where two complimentary observables were known?

 

[Goldstone1]

I had similar ideas, subject to verification.



how? can you give an example/experiment where two complimentary observables were known?

Well, you can only know one with great certainty, but the other becomes increasingly unknowable, which is what was meant by the post.

 

[Goldstone1]

That doesn't mean it is random though.

We seem to also use the radiation of ripe systems as a perfect example of random systems. I don't see why... 1) If there is a mechanism, then it isn't random 2) you can freeze the system using the zeno effect, then your system of radiating particles are completely knowable over large periods of time.

 

[San K]

Just a point: You can't really say that a specific property is always random or not, it depends on the context, and how you have prepare a particular state. For example, a photon in a Fock state has a known photon number, but an unknown (random) phase, whereas a photon prepared in a coherent state may have a well known phase, but instead containing an unknown (random) number of photons.

I did not understand the "photon number" part.

a photon prepared in a coherent state may have a well known phase, but instead containing an unknown (random) number of photons.

If we have two photons in a coherent state, don't we have a well know phase as well as a known number of photons (i.e. two)?

 

[Goldstone1]

To say it was random, you would need to explain a large part of decoherence physics.

[tex]|\psi> = \sum_i |i><i|\psi>[/tex]

would be our state of the system also knowing that the [tex]|i>[/tex]'s form the Einselection basis. If one says the initial state of the system was [tex]\epsilon[/tex], then one can make a before and after equation based on what has happened in it's evolution. In effect, a system can either loose information or gain information. If we are talking about radiative systems, giving off radiation, then the after equation

[tex]|A>= \sum_i |\epsilon_i><i| \psi>[/tex]

If one can ultimately know how strongly [tex]|i>|\epsilon>[/tex] evolves into [tex]\epsilon_i[/tex] is completely knowable, because there is nothing which dictates in the equations that it cannot be knowable.

 

[Zarqon]

I did not understand the "photon number" part.

photon number = number of photons

If we have two photons in a coherent state, don't we have a well know phase as well as a known number of photons (i.e. two)?

A coherent state is per definition a superposition of photon number states. As soon as you have one well defined photon number, then it must also have an unknown phase, because you cannot even define a phase for only one photon number, since a phase is a relative concept.

Simple example:

A state with exactly two photons can be written |2>, and there is only one possibility. However, a state with randomly either 1 or 2 photons could be written in a infinite number of ways, for example, |1> + |2> or |1> - |2>. The latter ones are coherent states and the phase is the difference in sign between the individual photon number states.

 

[San K]

photon number = number of photons
A coherent state is per definition a superposition of photon number states. As soon as you have one well defined photon number, then it must also have an unknown phase, because you cannot even define a phase for only one photon number, since a phase is a relative concept.

Simple example:

A state with exactly two photons can be written |2>, and there is only one possibility. However, a state with randomly either 1 or 2 photons could be written in a infinite number of ways, for example, |1> + |2> or |1> - |2>. The latter ones are coherent states and the phase is the difference in sign between the individual photon number states.

well put, this and the previous post. thanks for info

 

[Goldstone1]

well put, this and the previous post. thanks for info

But their post does not prove a true random system. No part of it actually says random, it says ''lack of knowledge''. This is a priori of the argument solicitated, but understand lack of knowledge is just a part of ignorance. No system is incomplete and beyond the reach of human evolution.