An answer to another question mentions that
There are arguments that suggests that such machines ["quantum Turing machines"] cannot even be built...
I'm not sure I fully understand the problem, so perhaps I'm not asking the right question, but here's what I could gather.
The slides are presented in a lecture (from 2013) by Professor Gil Kalai (Hebrew University of Jerusalem and Yale University). I watched most of the lecture, and it seems his claim is that there is a barrier to creating fault-tolerant quantum computers (FTCQ), and this barrier probably lies around creating logical qubits from physical components. (timestamp 26:20):
It sounds like the reason for such a barrier is due to the problem of noise and error-correction. And even though current research takes into account noise, it doesn't do so in the right manner (this is the part I don't understand).
I know many people (e.g., Scott Aaronson) are skeptical of this claim of impossibility, but I'm just trying to better understand the argument:
What is the reason for suggesting that practical quantum computers cannot be built (as presented by Professor Gil Kalai, and has anything changed since 2013)?