Let me state this right up front - quantum computing is a boondoggle. I won't go so far as to say it's a scam, because we're talking about true believers here.
Quantum computing is nothing more than analog computing. Yes, you read that correctly.
You can replicate the performance of a quantum computer with hydraulics. This has already been done.
The best current quantum computers act as nothing more than random number generators. You can do this with a microphone for ambient noise, or an antenna to detect cosmic rays.
You can perfectly replicate an entangled particle pair with a random bit generator and a NOT gate. This is all that quantum computing has to offer us.