A Quantum Experiment I can't predict the outcome

Great Debates
1

Hello people, prepare for the long post

Just a bit of context:
I’m a software developer and during last year a lot news about quantum computing showed up and I spent a lot researching it on my own out of curiosity, So I’m aware I can make wrong assumptions and/or not understand, what some of you may consider basic in the subject. My grammar may fail too, as I’m not a English native speaker. For case of any, I’m sorry beforehand;

Let’s talk about the more common experiment they first show us, the double slit experiment. Considering that small enough particles change their behaviour as we observe it or not; they are in superposition until we interact, in some way affecting even the past.

(Kinda off-topic: First thing I cannot reach at any conclusion is if computers count as observers, classical ones probably do as they can only assume one state or the other, but in the other hand there’s no ‘person’ watching until it shows up on the screen a result, right?
I can’t answer that myself.)

Now let’s say I have a quantum computer (I assume this one can keep the result and keep it without interference until I try to see it).

Now let’s say we do have a quantum computer and it work as I image it, and that I’m able to make a game in it…

I have a sensor that perform the double slit test (using photons, maybe), the output of it will all be a secret, no one will ever see it if we do ask it to do so. The hidden output are two:

  1. if either acted as a particle or wave
  2. which slit was used by the photon

Using the assumption that everything will be in superposition if nobody tries to watch the results now follow this algorithm:

1: Execute the slit test, keep the result from the user;
2: If the output was a wave let’s show a Square
3: Else I show a triangle
4: Wait some time and show a two-option choices, Yes or No
5: If Yes was choosen, I show where the particle passed by, using the second output
6: Else, we destroy any evidence we had about which way the particle went, nobody will ever know;

Now, how will this work? Would the user see different results depending on his later action? I know I’m breaking the rule of causality here, but I cannot reach to an outcome having the knowledge I have right now.

Does anyone clear this to me?

2

The double slit experiment always produces an interference pattern. Hence minds being blown when firing only a single photon at a time and you still get the interference pattern as expected from waves (not individual particles).

It seems you want to set up a Schodinger’s Cat sort of experiment, where you fire single photons and the unobserved component would be whether you were using a single slit or a double slit.

From there, it’s anybody’s guess. I’m no physicist or computer scientist.

3

I am not an expert on quantum physics, but:

You can’t say that the photon went through one slit or the other, because by definition IF it did, you wouldn’t have an interference pattern- you’d have a wave pattern emanating from one slit or the other.

The confusion is that if you think of light as little particles called photons, then intuitively you expect them to be localized- that at any point in time they would have a definite position in space. But although photons are quanta, quanta aren’t particles in the classical sense. The difference between classical particles, classical waves and quanta is that like waves quanta have a only a probablistic location; but unlike classical waves and like classical particles, quanta come in chunks, having energy in fixed multiples of a fundamental value, in this case based on Planck’s Constant.

The best I can tell you is that photons act like particles when they’re emitted and absorbed, and like waves inbetween.

4

Thanks for both answers!

What I get from what you’re explaining to me is that the moment the photon passes through one slit my equipment that verifies the photon would call it a particle because it had to be absorbed by the same equipment in the slit and causing it never hit what’s behind it and not causing the interference pattern, did I get it right?

I completely ignored the fact that to know the position of the photon I must absorb it

5

I was just reading about this very aspect in a book on QM that attempts to dispel or re-interpret an alternative to the Copenhagen Interpretation.

They have an excellent illustration on par with what you’re on about here if I recall correctly, but it’ll take me a little to look up the chapter.

I’ll return soon.

6

What you’re trying to describe is the delayed choice quantum eraser

Don’t get too caught up on wave-particle duality though. The actual physical objects in quantum mechanics are particles.

7

Asympotically fat,
that experiment presents the same idea I was trying to explain!

I’ll read more about it, thank you!

8

FWIW the book I was reading is called Quantum Enigma by Bruce Rosenblum and Fred Kuttner.