Observers

arfa brane said:
From Wikipedia:



So the Bloch sphere is a re-labelled Riemann sphere? And since it's also the complex projective line, maybe there's a way to view entanglement in that context?
Except, you have two spheres, or projective lines. Their product is a tensor space, sort of a vector with twice as many dimensions.

Also note that because this Hilbert space 'drops' into the same one where coins have real probabilities--measurements are real-valued--you can do some of the gating stuff with real vectors, the tensor products are then quite trivial: 00 is the tensor product of two 0-states (I've omitted the Dirac notation), and so on. Tensoring two real bits (not qubits) gives a real 2-bit register.

Like the example you see of an XOR gate being equivalent to a CNOT gate, modulo some thing or other.
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Now we're getting somewhere. Complex numbers are quite useful for engineering; without them it would be impossible to do something simple like design a Tcebychev filter, some of the coolest use of complex math there is. I'm saying only, there are inappropriate places to use it, and making the speed of light proportional to time would be one of those situations. We really do need an entanglement clock before an entanglement based hypercomputer is going to work.

An XOR gate almost resembles an entanglement test (anti coincidence) all by itself, like it could be an entangled/not entangled gate used for synchronization of the qubits. Could we make an XOR gate system synchronized to observation? It has to be photonic, unless Delft can do it with Majorana fermions and superconductors. Entangled photons are easier to adjust timing with fiber optics.

Observing an entangled state is going to simultaneously flip the state of one (or all) of the other entangled states. An entanglement gate would have to do this, even if this isn't necessarily what it is you wish to happen.
 
danshawen said:
We really do need an entanglement clock before an entanglement based hypercomputer is going to work.
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That isn't something I've heard of.
Can you explain why we need one, and what one is?

It's just that time isn't really a feature of quantum gates except for the time it takes for inputs to become outputs, the other place time appears is when you measure states.
What is important is that the inputs have to not be erased, as in classical logic gates. Everything has to be computationally reversible which means being able to compute the inputs for a given set of outputs. Otherwise there isn't a system clock at all, likewise an XOR gate doesn't have or need a clocking mechanism.

Reversibility is a requirement, but actual reverse computation isn't.
 
Write4U said:
Two questions about the second experiment;
a) Can the effect of non-interference be attributed to polarization?
b) Is the mirror function in the experiment of any consequence, other than simply redirecting the path of the photon?
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Do you mean this experiment, the CNOT gate?

Screenshot from 2017-05-16 13-59-30.png
 
arfa brane said:
Do you mean this experiment, the CNOT gate?

View attachment 1454
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Yes,.
Is it possible that the mirrors alter the properties of the photons, so that they no longer recognize each other's wave orientation? We do this with polarized sunglasses, which eliminates extraneous glare reflected from say water or uncoming traffic.

p.s. Does a mirror collapse the wave function at the glass surface or at the reflected image, which may appears to have 3D properties.

IOW. photon ----> mirror surface | (collapse?) ----> apparent image (collapse?)
 
Write4U said:
Yes,.
Is it possible that the mirrors alter the properties of the photons, so that they no longer recognize each other's wave orientation? We do this with polarized sunglasses, which eliminates extraneous glare reflected from say water or uncoming traffic.

p.s. Does a mirror collapse the wave function at the glass surface or at the reflected image, which may appears to have 3D properties.

IOW. photon ----> mirror surface | (collapse?) ----> apparent image (collapse?)
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That's a simple one. The correct answer is, entanglement of a photon is conserved after it is reflected. Or at least one reference I consulted said that it was. This is a good example, entanglement is different for photons than it is for electrons. Folks seem to be trying both approaches to store and manipulate qubits.
 
Write4U said:
Yes,.
Is it possible that the mirrors alter the properties of the photons, so that they no longer recognize each other's wave orientation?
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Both beams reflect the same 'amount' off each mirror. Any phase change will be the same for both photons. I think polarization does occur at some angle, maybe the Brewster angle.
But the detectors, classical particle counters, aren't detecting polarization angles.

Another thing you can add is an arbitrary phase shifter in one beam, a quarter or half wave plate, then you will get interference effects.
You get interference any time there is a phase difference along two equal paths.
 
arfa brane said:
Both beams reflect the same 'amount' off each mirror. Any phase change will be the same for both photons. I think polarization does occur at some angle, maybe the Brewster angle.
But the detectors, classical particle counters, aren't detecting polarization angles.

Another thing you can add is an arbitrary phase shifter in one beam, a quarter or half wave plate, then you will get interference effects.
You get interference any time there is a phase difference along two equal paths.
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Likewise, as in the entangled photon version of the double slit experiment, classical interference / diffraction does not destroy or decohere entanglement either. Only trying to observe either slit by means of a detector, before or after the photon actually passes through one of the slits, changes what is observed. It is the same as choosing a phase angle to observe the source of the photon (a pair of entangled electrons in a cloud surrounding the atom). It is a hyper relativistic observation. Any fraction of a degree of arc separation in the electron cloud is sufficient separation to decohere the photons produced in this manner. The entangled electrons MUST be able to flip spins FTL. If they did not, a real photon, entangled or otherwise, could not be produced. In the case of hydrogen, the other charge is positive. Is it entangled? No idea.
 
danshawen said:
It is a hyper relativistic observation.
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Oh dear. There's another thing I've never seen before.
In what way can an observation be "hyper-relativistic"?
The entangled electrons MUST be able to flip spins FTL. If they did not, a real photon, entangled or otherwise, could not be produced.
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No, spin-flips occur in ordinary amounts of time, as far as I'm aware.
 
If spin flips ocurred in the same time it took a photon to traverse an atom, then neither the entangled double slit experiment, nor my positronium thought experiment' would work the way they do. Birgit actually did the experiment in 2002. It worked exactly as described, although Birgit had no explanation as to why.

Hyper relativistic means relativity with FTL entanglement spin flips.
 
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To recap the positronium thought experiment:

Let an atom of positronium decay inside of a cloud chamber so you can inspect the spiral condensate trails on an appropriate scale.

Freeze frame the decay process the instant just before the electron and the positron waveforms begin unraveling each other.

From the exact center, have a look around the freeze frame. How much light travel time would it take to change the right hand spiral into a left handed spiral? Answer: exactly zero light travel time.

What is the state of electrical charge at the center of the colliding matter-antimatter? Answer: zero electrical charge.

Is the electron quantum entangled with the positron? Answer: yes.

Now unfreeze time and let the photons (gamma rays, in this case) fly in opposite axial directions to the spiral.

Are the released gamma radiation photons entangled? Answer: yes.

If quantum spin angular momentum is conserved, and ignoring any limitations set by Special Relativity for the purposes of this question, what was the angular velocity of the electron-positron pair just before the positronium self-annhilated? Masses / energies, spins, and sizes of the particles are known. Don't forget to consider relativistic mass increase. According to Feynman, the positron magnetic moment is 1000 times that of a proton. Open question.

http://www.feynmanlectures.caltech.edu/III_18.html
 
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danshawen said:
If spin flips ocurred in the same time it took a photon to traverse an atom, then neither the entangled double slit experiment, nor my positronium thought experiment' would work the way they do. Birgit actually did the experiment in 2002.
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Well, the thing is, it requires energy to flip the spin of any fermion. Energy isn't FTL. Measurement, requiring energy, isn't FTL.

The Bloch sphere says flipping a spin is equivalent to rotating a measurement basis. This can't be FTL either.
 
arfa brane said:
Well, the thing is, it requires energy to flip the spin of any fermion.
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According to Pauli's exclusion principle, every atomic energy level can contain two electrons; one spin up, the other spin down. They can have the SAME energy levels. This means they can flip together, simultanously, without the bulk transfer of any energy at all.

arfa brane said:
The Bloch sphere says flipping a spin is equivalent to rotating a measurement basis. This can't be FTL either.
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I believe the first part. I don't understand why quantum physicists seem to think, the mode of propagation of energy inside a particle is restrained to the same fundamental limitations for unbound energy, particularly since they don't even understand what boundary conditions it is that binds energy into a localized ball of energy in the first place. Is there a mathematical model for this, or is there not? "Ideal points" do not even define a differential volume for binding energy. So much for geometry. QFT makes particles into points BECAUSE it doesn't know how to deal with whatever force(s) bind particles like electrons together, or to put it another way, for whatever reason, they don't care.

What would it really hurt if a Bloch sphere represented an FTL phase angle change? Phase angles for entanglement don't need to be tied to the same limitations as the propagation of an unbound photon in a straight line. Entanglement doesn't "propagate" in the sense a velocity does at all.
 
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On a lighter note, but possibly related? An optical illusion of entanglement.

Why does my mind constantly draw me to the "mirror effect"?
I have a strong intuitive feeling that a mirror type function (such as entanglement) is a big part of the picture. Even on a physical level we have natural laws which indicate "for every function, there is an equal opposite function" IOW, a mirroring effect.

Speculative, but intriguing, IMO.
 
danshawen said:
According to Pauli's exclusion principle, every atomic energy level can contain two electrons; one spin up, the other spin down. They can have the SAME energy levels. This means they can flip together, simultanously, without the bulk transfer of any energy at all.
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Except that there is no way to measure this "spontaneous" spin flipping.

Perhaps what you describe does happen, but it if it can't be detected it can't be part of any QM experiment.
 
QuarkHead said:
OK. So your assertion is that an observed system behaves in exactly the same way as an unobserved system?

Or to put it another way; if I determine the eigenstate of a system to have particular value at a particular time, I may assume this system always to have had that particular value in the past and always will.
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But how would you ever be able to prove it since you would have to make an observation in order test it, which invalidates the whole question.

Why must you be able to assume the system always has that particular value? How could you prove it?
 
arfa brane said:
Except that there is no way to measure this "spontaneous" spin flipping.

Perhaps what you describe does happen, but it if it can't be detected it can't be part of any QM experiment.
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The reasons we wish to do quantum computing in the first place is in part because those entanglement flips have zero propagation delay, and a more nuanced means of exploiting superposition (for simulating quantum mechanical processes) is of course the other.

A zero prop delay NAND gate would be cool all by itself (to render conventional computing instantly). But the best engineering always comes with trade-offs and compromises. It likely will be no different with quantum computing. Clever ways to exploit entanglement without destroying the information or the computational power it teases us with will eventually come, just like being immersed in an inertialess space was not an impediment to our eventually developing a workable solid geometry. But the rules are dictated to us by nature, not the other way around. The first ones may be little more than an abacus that uses quantum spin liquids for beads.
 
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danshawen said:
The first ones may be little more than an abacus that uses quantum spin liquids for beads.
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That reminded me of this remarkably simple experiment which produces the most amazing and profound configurations.

Such complicated repeating patterns, from such a simple configuration.
 
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I was just thinking, if I could flip the spin of an electron faster than light I could build a clock that has a frequency beyond measurement!

But I don't believe it's possible. Such a clock wouldn't be very useful, either.
 
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