# Which properties of the quantum are random?

• San K
In summary: Einselection basis. If one says the initial state of the system was \epsilon, 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.
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

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.

Demystifier said:
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?

San K said:
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.

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.

Zarqon said:
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?

San K said:
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.

Goldstone1 said:
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.

Goldstone1 said:
But knowing two complimentary observables

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

San K said:
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.

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.

Zarqon said:
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.

Zarqon said:
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)?

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

$$|\psi> = \sum_i |i><i|\psi>$$

would be our state of the system also knowing that the $$|i>$$'s form the Einselection basis. If one says the initial state of the system was $$\epsilon$$, 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

$$|A>= \sum_i |\epsilon_i><i| \psi>$$

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

San K said:
I did not understand the "photon number" part.

photon number = number of photons

San K said:
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.

Zarqon said:
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

San K said:
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.

## 1. What is quantum randomness?

Quantum randomness refers to the inherent unpredictability of certain physical systems at the quantum level. It is a fundamental property of quantum mechanics and is often described as the behavior of particles being governed by probability rather than determinism.

## 2. Are all properties of the quantum random?

No, not all properties of the quantum are random. Some properties, such as position and energy, can be measured and predicted with a certain level of accuracy. However, other properties, like spin or momentum, are inherently random and cannot be precisely determined.

## 3. How is quantum randomness different from classical randomness?

Quantum randomness is different from classical randomness in that it is not due to a lack of knowledge or information about a system. Instead, it is a fundamental aspect of the quantum world and is not subject to the same laws and principles that govern classical systems.

## 4. Can we control or manipulate quantum randomness?

At the current stage of scientific understanding, we are unable to control or manipulate quantum randomness. It is an inherent property of the quantum world and cannot be altered or predicted with certainty.

## 5. What are the practical applications of quantum randomness?

Quantum randomness has several practical applications in fields such as cryptography, quantum computing, and quantum communication. It is also being studied for its potential use in creating truly random number generators.

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