This video shows that in all likelihood quantum computers will never work, anyway not when it comes to simulating chemical reactions where electron pairs play a role.
Let me explain: The SG experiment is of course the Stern-Gerlach experiment from 1922 for readers who do not know that. That was the experimental discovery of electron spin although Stern and Gerlach wanted to prove something very different. Now as far as I know a repeated SG experiment, or a sequential experiment, has never been done. Likely it has been tried a few times but as far as I know nobody succeeded into getting the desired results and as such proving the probalistic nature of measuring electron spin. Since 2015 I have been looking for this but until now I found nothing.
In this video at about 08:09 min into the video Katie claims that after the original SG experiment from 1922 countless experiments have been done where a sequence of such experiments was done. See the image below, the Z and X just denote the derection of the applied magnetic field. These kind of experiments just have no result.
In video’s like this you always hear the names of Stern and Gerlach but never ever the folks who would have done such a repeated experiment.

And again for readers unfamiliar with what I think of electron magnetism, I think that electron magnetism is just as electron electricity: It is a monopole and permanent charge. So there are two kinds of electrons that have the same electric charge and opposite magnetic charges. On top of that I think the magnetic charge is permanent so it can’t be flipped and measuring the spin is not a probabilistic event. It’s permanent…
I made a few screenshots from the usual nonsense in the sense it is not rooted in experimental evidence:

For myself speaking I do not understand why so many people think that these experiments are actually done. Since I was a bit annoyed by the video, with a simple internet search in only a minute or three I found a nice pdf from MIT the Open Courseware stuff. Let me quote from page 5:

Let us now consider thought experiments in which we put a few SG apparatus in series.

Oh, now it’s watered down to “Considering thought experiments”? Well if you want to read the thing, here it is:
SPIN ONE-HALF, BRAS, KETS, AND OPERATORS

And of course the video:

Another interesting point is that you can do the Stern-Gerlach experiment for yourself! On an IBM quantum computer! Lets leave it with that.