A misconception that can exist, in Quantum Mechanics.

First of all, I need to admit that I did not study Quantum Mechanics. I did study Physics, however, and have had numerous discussions with people, who either:

  • Studied Quantum Mechanics independently, Or
  • Studied Quantum Mechanics formally.

And those discussions have made me aware of a misconception that can exist, about how the wave-function of particles lead to measurement, but which will certainly not exist, for people who have studied the subject formally.

I have already made a posting, about The Myth Of Wave-Particle Duality, in which I highlighted what I see as an absurdity, in how the wave-function of particles is commonly defined. And, having written that, I should also point out, that the common sense which QM applies, not to treat Complex Eigenvalues as representing real properties of a particle, fails to spill over, to Complex Probabilities.

Even though the wave function of certain particles can be taken to exist factually, attempts to measure it as belonging to one particle will cause it to collapse. However, the way some people may visualize it, would be, that the wave-function continues to exist, simply because the Universe seems to be filled with waves, that continue to exist. And this is an especially possible misinterpretation of QM when the particle in question is a photon, just because low-energy photons, that lead to long and obvious wavelengths – i.e., radio waves and light from lasers – are so commonplace.

What happens with these obvious waves is that, most of the time, a large number of photons contribute to those waves, in such a way that each photon is being absorbed, in order for the actual wave to have been measured. And, when the photon is absorbed, as I have written elsewhere, it has also been ‘witnessed’, so that it is no longer in a superposed state. And, because one photon has been absorbed, it has also ceased to exist.

Even the way photons ‘work’ changes drastically, when individual photons have been measured. Modern physics is capable of measuring individual photons. When this happens, the detection of one photon either took place or did not. This can also loosely be described as ‘a click’, in contrast with ‘a wavelike phenomenon’, even if a more sophisticated method has been used, than methods that produce audible clicks. And it continues to be true for the low-energy photons, of which there will typically be a greater number, as it was with high-energy photons, that Historical Technologies such as a Geiger Counter were able to detect. This digital existence of single photons, when measured as such, is universal.

I suppose that a valid question which the reader may next ask could be, ‘How would this apply to Quantum Computing, which factually performs computations, based on wave-functions?’ And, there are basically two types of answers which I can think of. The actual Quantum Computer is a tiny device, that can work with individual photons, But:

  • When Scientists measure the output of a Quantum Computer, they may be using a larger number of actual Quantum Computers, all performing exactly the same computation, but in such a way that the combined light intensity is high enough to be measured directly at any instant in time, Or
  • They may be amplifying the photon which one Quantum Computing core actually outputs, so that one output photon leads to a more macroscopic phenomenon, through which Scientists can read the result of a Quantum Computation, Or
  • The optics of a single Quantum Computing core can cause numerous photons to perform the same computation.

Either way, even though the state within the Quantum Computer was defined in terms of QBits, what gets measured as output, is no longer so. Therefore, the Quantum Algorithm needs to be programmed in such a way, that the ability either to measure a photon or not to, will still lead to a successful experiment.

What I do know additionally is, that if the photon output by a Quantum Computer has been amplified, let’s say by a laser-like device, any superposition of the wave-function of the original photon has been collapsed, because, when lasers are used as light amplifiers, they also witness the Quantum State of the initial photon. (:1) At that point, the Quantum Computation has definitely ended.


 

 

One of the more remarkable observations I seem to have made about QM is, that ordinary refraction or reflection of light, such as by metallic surfaces or glass, does not seem to witness the photons. Anecdotally, the reader may present himself to his washroom mirror in the morning, secure in the knowledge that the mirror did not witness what the reader sees.  ;-) This form of light can continue in some superposed state. The reason I’ve concluded this, is the large number of experiments which Scientists carry out, and then write about, and which still seem to succeed, in spite of the fact that the Scientist’s apparatus has refracted or reflected the light used.

Now, whether the Scientist actually noticed, that he was refracting or reflecting the light, is a separate question. I suppose that if the experiment failed, the next thing the Scientist will naturally do, is search for why…

(Updated 7/12/2020, 14h55… )

Continue reading A misconception that can exist, in Quantum Mechanics.

Designing a Cir-Pol Sensitive to Left-Handed Light.

A concept which the reader may already be familiar with, is a Circular Polarizer, which first linearly polarizes light, and then renders the result circularly-polarized. But somebody might be interested, in creating a filter which is only sensitive to light circularly-polarized in one direction. Well, it turns out that this is as straightforward to achieve, as the first example, if we can assume that we have a birefringent layer, light with one known wavelength, and that we can adjust the thickness of the birefringent layer as needed.

cir-pol-inv_1-svg

 

cir-pol-inv_4

 

If we assume that light can first be linearly polarized, and then passed through the birefringent layer, whose extraordinary and ordinary axes are both at a 45⁰ angle to that of the original plane-polarization, then due to the higher refractive index of the extraordinary axis, its wave-function – i.e., dipole-moment – will become delayed with respect to that of the ordinary axis, until the former is phase-delayed by 90⁰, which is also 1/4 the wavelength of the light, with respect to the latter. In the example shown above, left-handed, circularly-polarized light has been achieved.

But the question could next be asked, what would happen if, we passed this helical beam of light, whose dipole-moments propagate as a left-handed helix, through another birefringent layer, that exactly matches the previous one. And the result which we’d obtain, is that the phase-position of the wave-function along the extraordinary axis, which has already been phase-delayed 90⁰, will be phase-delayed again, by another 90⁰, so that now its phase-position will be at 180⁰ to that, along the ordinary axis. And so where the diagram above showed full amplitude, it will consistently show zero amplitude, and full amplitude will take place perpendicularly, to where it had been before.

Thus, by controlling in which direction the extraordinary layer is followed by the transmitting direction of the linear polarizer that comes next, we can control whether the combination will be sensitive to left-handed or right-handed light.

I suppose that the mental exercise can be taken one step further, and we can ask what would happen, if directly after circularly-polarized light was achieved, said beam was bounced off a metallic mirror, with the directions of propagation before and after, ‘normal’ to the surface of that mirror.

Continue reading Designing a Cir-Pol Sensitive to Left-Handed Light.

Mirrors

I’ve read, that essentially there exist three types of reflections in Physics:

  1. Metallic
  2. Non-Metallic
  3. Total Internal Reflection (See Below)

Metallic reflections (almost) tend to preserve the polarization of the light (except for what’s written below), while non-metallic reflections tend to polarize the light. The latter are also the basis for “polarizing mirrors”.

Beam-splitters are essentially polarizing mirrors:

  • When randomly-polarized light hits them, the deflected beam will be plane-polarized in one direction, while the transmitted beam will contain, what the deflected beam does not contain.
  • When circularly-polarized light hits them, nothing really prevents them from splitting the beam.
  • When plane-polarized light hits them, depending on the angle of polarization, the amplitude of one emerging beam can become much lower, than that of the other. This is probably also why, linear polarizers can interfere with the physical auto-focus of a DSLR-camera.

(Edit 02/25/2018 :

Even though the articles I gave above ‘seem complete’, only today I’ve learned that they need to be modified. Specifically, the deflected beam is only polarized perfectly, when the incident beam strikes a non-metallic mirror at Brewster’s Angle. And I have no reason to think, that this account is wrong. )

From what I read, reflection, according to the particle depiction, takes place, because photons couple with plasmons, to form surface-polaritons.

From what I read, refraction takes place, according to the particle depiction, because photons couple with excitons, to form photon-excition polaritons.

(Updated 02/27/2018 : )

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