Re: On the uncertainty principle for photons. An experimental counter

On 11 , 08:50, "Rich L." <ralivings...@xxxxxxxxxxxxx> wrote:
On Nov 9, 6:56 am, kvblake <kvblake2...@xxxxxxxxx> wrote:
..



Sorry I've never read anywhere about imaginery wavelength. I would
highly appreciate if you can cite a textbook or a website where this
is analysed.
In a past article in this thread Eliot Spech wrote about imaginary
part of the momentum.
I also dont know nothing about this no have ever seen in a textbook on
QM.

Look up "evanescent waves" in wikipedia, or in most optics text books
(I don't have one with me at the moment to cite). You encounter the
same mathematics in the theory of waveguides, when the width of the
waveguide is smaller than the wavelength of the wave. In all these
cases, the wave number "k" becomes imaginary in the direction down the
waveguide, (or away from the surface in the case of evanescent
waves). The result of "k" being imaginary is that the exponential is
decaying, whereas the real "k" results in an oscillitory wave.







3. What about that sectioin where there is no tube. The particle
(photon) is not limited in X,Y - the wave diffracts there and many of
the photons which had passed part 1 of the tube should spread; but not
this one which goes into part 2 of the tube. It is not confined by the
walls and nevertheless I can't imagine it has been travelling some
other path but straight line into part 2. I can't imagine one of the
spread photons can turn and come into part 2 and travel then in
straight line.

Once the photon is in free space you can no longer say with certainty
where it is, or was. Just because it came out of a small hole in one
place and entered a small hole in another does not mean the photon had
to traverse a direct straight line between those two points. There
are many experiments in diffraction that demonstrate this.

OK. Let the photons fly all those crooked paths of Feynmann. I hope
the speed is still constant.
Then if one puts a time 'filter' and gets one click on the detector
he would know the path better than h/p = lambda?

It is not practical to set a time "filter" (more commonly called a
time "gate") so tight that you could perfectly determine the path of
the photon. In certain cases you can limit the range of the photon,
but never enough to violate the uncertainty principle. A very
interesting and accessible paper on some real experiments on this
subject are athttp://arxiv.org/abs/quant-ph/9501016v1.



For something that is much more difficult to
make sense of, and fundamental to Quantum Mechanics, study the EPR
paradox, Bells Inequality, and the Aspect experiments based on them.
Then look up Quantum Eraser Experiment. These all have decent
articles on Wikipedia.

The most weird for me is the behaviour of a single photon in Mach-
Zehnder interferometer.

Regards:Kevin- Hide quoted text -

- Show quoted text -

Rich L.- -

- -

Thank you very much for directions.
One question: Did Heisenberg knew that?
I dont think I understand the movement of photons or other particles
no I think anywhere is a clear explanation.

Just let see a whole new example- very simple - a slot and a screen.

Before the slot one could not tell where the particle could go (the
momentum is undefined in parallel to the slot directions). Heisenberg
principle.

But if I register a particle on the screen - I know it originated from
the slot. So all the possible 'paths' would lie in a cone with a top
in the registration point and base the slot. Very near to the region
of absorption (registration) the uncertainty would tend to zero thus
breaking Heisenberg principle. Or else the particle must makes jumps
with infinite velocity.

So I think the Heisenberg principle applies only before registartion
of a particle.
The particles must have (if are points) paths and we know where a
particle was going through space when we register it.
The photon do not have parts which travel different paths (as it seems
to be in Mach-Zehnder).

Regards:Kevin

.

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