Counterfactual computation

A physically possible wave-like influence doesn't start and stop instantly either, so that makes good sense.

Jeroen Belleman

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Jeroen Belleman
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TDs seemed to be reliable. But if you can verify that a scope has a bad TD, I have a modest collection of them and could donate a few.

They are easy to test. All you need is a function generator and a working scope, and maybe a resistor.

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John Larkin   Highland Technology, Inc   trk 

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John Larkin

Thank you very much for the kind offer, but unfortunately (?) I have too much other stuff to do at the moment (better paying but less fun), so diagnosing the 475s will have to wait. Anyway thank you.

Chris

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Chris Jones

This?

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I skimmed it... (I'm not much of a non-linear optics type.) But I think those are correlated down converted 'photons'. And not entangled. All entangled photons are correlated, most correlated photons are not entangled. (I think that is right.)

Making entangled photons is hard.. And the only 'cool' experiment I know of to do with them is the Bell inequality measurement... Which is not that showy... no nice pictures. So they don't get reported much.

George H.

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George Herold

Mmh. I think I agree, except that I think in terms of waves and signals, not photons.

An entangled pair carries some complementary information, so that if you measure one, you can foretell the result of the identical measurement on the other, but neither alone will give a definite result.

I should see if I can come up with an RF signal processing equivalent of such an experiment. Hold on...

Jeroen Belleman

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Jeroen Belleman

Grin, no worries I'm pretty sure that EM radiation behaves the same regardless of frequency. It's a matter of what detectors you have.

In the 'visible' photons are entangled in their polarization. I'm trying to think of an RF source where the polarization is unknown.. or can have any value.

George H.

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George Herold

I have a collection of beautiful Tek 547s and a zillion plugins that I planned to restore some day. If I'm eternally too busy to do that, I guess that's OK too.

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John Larkin

ISTR that Planck had a good try at that around 1900. ;)

A single scintillation is detectable, but it's only statistically _predictable_. The cat thing IIRC is an argument that you could have a macroscopic object in a mixed quantum state--QM doesn't apply merely on the atomic scale.

Cheers

Phil Hobbs

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Phil Hobbs

Thinking of a photon as an elementary excitation rather than a wavy billiard ball renders that a whole lot less mysterious, I think. You get to use Maxwell's equations, and compute the probability density of detection events vs. position.

It's the interaction of light with matter that's really mysterious.

Cheers

Phil Hobbs

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Phil Hobbs

Not sure. You can make a reasonably regularly-spaced sequence of quantum transitions via coulomb blockade. If you picked the right transition, and arranged the geometry so that only one EM mode was coupled to it, you might be able to do that.

Cheers

Phil Hobbs

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Phil Hobbs

Even if the cat's lot is determined by some quantum event, it's silly to pretend that its state is a superposition of all possible states. That may be a mathematically convenient way of treating the problem, but in practice you'll always have one outcome per event. This so-called superposition is really just the admission of our ignorance regarding the cat's fate. To pretend anything else would be mysticism.

The probability distribution will become evident only after having sacrificed a lot of cats.

Jeroen Belleman

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Jeroen Belleman

I would use the phase in lieu of the polarization.

Jeroen Belleman

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Jeroen Belleman

That may end up with a device that shoots electron peas on demand, but I'll admit I'm wrong only if someone manages to shoot photons with it. Such a device would finally bring a definite answer to whether it's either the field that is quantized, or rather just its interaction with matter.

Jeroen Belleman

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Jeroen Belleman

Nobody AFAIK was expecting Schroedinger's cat to be a practical experiment any more than Einstein's relativistic elevator.

Once it's known. That's sort of the point of the exercise.

That's an *a priori* assumption. I'm sort of a mystic myself, but not about physics. ;)

Well, virtual cats. Keeping the mixed state intact would probably involve cooling the cat down to some nanokelvins, which might bias the results a bit. ;)

Cheers

Phil Hobbs

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Phil Hobbs

I'm with you there.

Cheers

Phil Hobbs

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Phil Hobbs

quality

t

Hmm, Let's say you're allowed some device with only probabilities. So you push a button and one out of X times you get a photon. If X was ten would that be a photon gun? (I'm thinking of single atom/defect sources, some blast of laser light and a confocal microscope to focus on one. X is the fraction of 2*pi steradians I can catch...

1/10th is probably too greedy.) Photons are created at 'atoms' and destroyed/ detected at others. I don't see how having a single photon gun is any different than a single photon detector. (except the gun is harder technically. :^)

George H.

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George Herold

Is there a classical explanation for the behavior of a half-silvered mirror, a beam splitter? It can't split a photon.

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John Larkin         Highland Technology, Inc 

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John Larkin

It can, it does, and you can recombine them to get interference fringes. That's kinda the point of wave-particle duality.

Clifford Heath.

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Clifford Heath

If you use two single-photon detectors after the splitter, you'll see that each photon goes one way or the other. That's not very classical.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin
[Snip!]

Don't you have that backwards? It's the QM interpretation that requires it to split a photon to take multiple paths.

In the classical view it splits a wave, which is nothing mysterious. The problem is that you can detect the wave only by its effect on matter, which is quantized and probabilistic.

Come to think of it, I've become so accustomed to the existence of EM fields and waves that I hardly pause at the mystery of their existence and propagation in a perfect vacuum.

Jeroen Belleman

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Jeroen Belleman

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