A wave function does not collapse upon detection?

Every time I ask this, some do-gooder will not read a word I wrote and send me a video of the basic slit experiment and think they've somehow educated me. Every time. It's amazing.

What I'm looking for is a photo or video of a real experiment showing just two groupings. There a million photos/videos of the wave pattern. I'm looking for an example with exactly two clumps of photons because the light is observed as it passes each slit. In real life, not a computer simulation.

Watch this video if you're unclear what I'm asking: https://youtu.be/Q1YqgPAtzho

You take a shoe lace. You tie a loose knot in it. Prevent the extremities of the lace to move, by placing your feet on them (or rocks, or whatever). Put your finger inside the knot and slide the knot along the rope.

You have just played with a "particle". The knot is the particle.

Pinch the rope with your left hand somewhere along the rope. Pinch the rope with your right hand somewhere along the rope. Slide your fingers along the rope to bring them together. This will progressively tighten the rope between the fingers. Alternatively you can just tighten the rope by pulling on it.

If there is knot in the region you just tighten, congratulation you have just measured your first particle. If not, try again by placing your finger at different spot, and try again you may get lucky. Quantum physics is a matter of probabilities.

Now that you have caught your particle, you have to loosen the knot, so you can explain the uncertainty principle.

Once you have played with one knot. Try adding a second knot, move them. Can you get one to go through the other ? Is the number of knots on the rope always conserved ?

Now that you have played with knots, here is a fun twist. You need to have a flat lace or a belt though. Lay the flat lace flat. Do a half twist on an extremity of the lace. And like you did with the knot before, slide the half twist along the lace between your fingers, tightening and loosening it as you like. Congratulation you have discovered another type of particle. Try adding another half-twist. How do the twist interact along the rope ? Did you succeed in making them disappear. And can you create a pair of particle out of nothing by twisting the lace in the middle ?

If it feels too easy for your 5-year old, you can now show him the belt trick to continuously rotate a cube attached by its faces https://en.wikipedia.org/wiki/File:Belt_Trick.ogv and he will have a better grasp on what an electron is than 99% of high-school students.

This analogy can be extended for more complicated kind of knots, twists, elements of lie algebras... And you can also extend it from the 1d case of the rope to 2d case of a fabric (twist along one dimension, twist along the other dimension...), 3d case.

If you want to learn more about physics, don't throw the lace away, you can play with it in a ton of different ways (vibrating modes of energy...), even before needing to introduce springs; but that's a story for another day.

1, which is very practical, is that it doesn't explain why the wave function always decoheres in the same way. In experiments, you can always chose the basis of measurement, and get some definite results in that particular basis, while the properties in another basis remain indefinite. But, in classical reality, all objects have definite properties in the same basis (say, positions in the same Cartesian coordinate system). This is known as the preferred basis problem, and decoherence can't explain it.

2, which is somewhat more philosophical, decoherence doesn't explain the quantitative relationship between the wave function and the probability of observing a particular outcome. Indeed, in MWI it's very hard to even define probability in a coherent way, since all outcomes actually happen and there is an uncountable (in the mathematical sense) number of outcomes.

Can you give some examples of such bases? Position is one, for sure. In "Quantum Mechanics 101" we are told that momentum is another, but I'm sceptical that there is a real experiment that can measure momentum without also measuring position.