[immibis]

No, it's all well-defined science. There's known mathematics for how the operations you do affect the probability distribution of the answer. The initial state can be prepared. It can't be measured after it's been prepared, because that would ruin it. But so what - that happens all the time in science. Your comment is like saying chemistry is a pseudoscience because if we put a pH indicator strip in before doing a certain reaction to prove it's an acid, the contamination by the indicator chemical stops the reaction from working.

We can simulate a quantum computer using a normal computer (in exponential time). Simulations of tiny quantum computers agree with the experiments using tiny quantum computers. We can also simulate less-tiny (but still pretty small because it takes exponential time) quantum computers. But we haven't built an actual one of those yet. It seems they're really hard to build But also no fundamental reason is known why it should be impossible to build one. Shouldn't it just be the same as a tiny one, but bigger? The tiny ones were hard enough to build, so maybe it's just really hard and we need better techniques.

Perhaps it will turn out to be a failed branch of science that leads to no practical applications, but it's certainly real science, studying real things and making testable predictions (which are true so far). I suppose your next objection will be that since we only have tiny quantum computers, non-tiny problems are pseudoscience, but that's like saying particle physics was pseudoscience before we built the Large Hadron Collider.

Recently 3Blue1Brown made a video attempting to explain Grover's algorithm, which is one of the main applications of quantum computing, that also covers basic ideas of quantum computing and some common misconceptions - have you seen it yet? https://www.youtube.com/watch?v=RQWpF2Gb-gU and followup: https://www.youtube.com/watch?v=Dlsa9EBKDGI

[_heimdall]

You're describing a field based on simulations and predictions. That is interesting, but it isn't scientific as you aren't actually testing anything when you only run simulations.

A simulation is an interesting indicator for future scientific research, but it is never scientific research in and of itself.

[immibis]

When your predictions are testable and agree with reality you did science.