Wave functions

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  • #1
daniel_i_l
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Why is the WF of the photon a physical wave - the EM wave, but the WF of all other matter are imaginary?
 

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  • #2
ZapperZ
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Where did you get the idea that the wavefunction for the photon is a "physical wave"? The EM wave that you get from the classical Maxwell equations is not the wavefunction of the photon.

Zz.
 
  • #3
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The EM wave that you get from the classical Maxwell equations is not the wavefunction of the photon.

But what is their realationship??? I asked that at PF already a couple of times and unfortunately never got a clear answer. Could someone be so kind and help?
 
  • #4
i'm no expert but the way i see it is that a wavefuction is just a mathematical abstraction used to predict the probibility of a photon's location, So wavefunctions aren't exactly physical objects you can "see" in a everyday sense
 
  • #5
daniel_i_l
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Does the EM wave have to do with the wave function of the photon? Are they connected?
 
  • #6
Tez
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daniel_i_l said:
Does the EM wave have to do with the wave function of the photon? Are they connected?

For certain quantum states of light, if you compute the mean value of the electric and magnetic field operators you find that they oscillate exactly according to the waves of the classical Maxwell theory. This is the most precise connection.

Another connection is to do with the "mode structure" - you can solve for the modes in a cavity, for example, by solving Mawell's equations with the boundary conditions. The quantum mechanical modes will be the same - its just that now its quantum states (not classical fields) that "pick up" the mode labels. And of course quantum states of light in these modes may behave quite differently to classical ones...
 
  • #7
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What is the photon?
The first, it is classical EM waves.
The second.
The sort pulse of this wave we can describe as a single wave named soliton. The soliton we can consider as local object i.e. as a particle.
The third.
The particle we are describe with Quantum-Mechanical Wave Function.
Conclusion
The photon we can consider as a classical Electromagnetic waves or as quantum object with wave function. You can see this two different description in the literature.
 
  • #8
daniel_i_l
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So how does the photon - a massless, chargeless particle - account for the effects of the EM wave. For example, how can the photon generate an electric field? Or is the electric field (and the magnetic field that it generates) just the classical description of the photon?
 
  • #9
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daniel_i_l said:
Or is the electric field (and the magnetic field that it generates) just the classical description of the photon?
Yes, that’s right. In addition, almost all effects, which we observe for the photons, are classical! The most number of the experiments used photons with classical properties. Only one exclusion there is. It is the case of entangled photons named bi-photons. The optic with bi-photons (entanglement photons) is quantum. It is Quantum Optic. All others kind of optical experiments are classical. It is classical optic with classical light.
 
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  • #10
jtbell
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daniel_i_l said:
Or is the electric field (and the magnetic field that it generates) just the classical description of the photon?

More precisely, electric and magnetic fields give a classical description of the net effect of bazillions of photons. If you're dealing with only a single photon, or a small number of photons, I don't think a description in terms of electric and magnetic fields is meaningful.
 
  • #11
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From “Fundamentals of Physics, Fifth edition, Volume 2” Halliday / Resnick / Walker
It’s not only an electromagnetic wave but it is also a probability wave. That is, to every point in a light wave we can attach a numerical probability (the square of the amplitude of the electric field vector) that a photon can be detected in any small volume centered on that point.
 
  • #12
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jtbell said:
More precisely, electric and magnetic fields give a classical description of the net effect of bazillions of photons. If you're dealing with only a single photon, or a small number of photons, I don't think a description in terms of electric and magnetic fields is meaningful.

We can directly measure the phase of an EM wave, such as in radio transceivers. What does that correspond to in thinking of photons?
 
  • #13
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Ring said:
From “Fundamentals of Physics, Fifth edition, Volume 2” Halliday / Resnick / Walker
It’s not only an electromagnetic wave but it is also a probability wave. That is, to every point in a light wave we can attach a numerical probability (the square of the amplitude of the electric field vector) that a photon can be detected in any small volume centered on that point.
That's interesting.
 
  • #14
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jtbell said:
More precisely, electric and magnetic fields give a classical description of the net effect of bazillions of photons. If you're dealing with only a single photon, or a small number of photons, I don't think a description in terms of electric and magnetic fields is meaningful.
Yes, it is more exactly and better than I wrote in my post before.
 
  • #15
Tez
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jtbell said:
If you're dealing with only a single photon, or a small number of photons, I don't think a description in terms of electric and magnetic fields is meaningful.

Even if you're dealing with a lot of photons the EM field description may not be useful - the simplest example is a Fock (number) state of n photons (normally written |n>) for some large value of n. For such a state there is no mean oscillating field (in fact the phase, which is conjugate to photon number, isn't defined).
 

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