My question is definitely regarding quantum-speedup but the quantum-speedup tag is confined to algorithms... and my question is definitely not on algorithms. So, this is just my best shot at tagging.
This article in Physics World discusses quantum speedup and makes some pretty provocative statements (examples below).
It also tells me that people in a forum like this one might feel as follows: “Some feel that this debate about the “how” of quantum computation is a red herring. “Researchers attending most conferences in quantum computing never mention these issues, or only in discussions over beer”.
Here are some of those "provocative statements".
“None of the explanations for how quantum computers achieve speed-up is universally accepted.”
“If it’s not from the vastness of Hilbert space, not from entanglement and not interference, then what? “As far as I am aware, right now it’s pretty silent in the theatre where this question is played out – that’s because the main candidates are all dead...”
Here are two specific questions. As a worker in this field, does the following statement from the 2014 Physics World article match your own perception here in 2018? If not, what are the favored candidates today? And again, this is not a question about speedups obtained via algorithmic refinement. Why exclude algorithmic refinement? See "Footnote".
"Deutsch’s notion of quantum parallelism has stuck – the standard explanation in popular descriptions of quantum-computing speed-up is still that massively parallel computation takes place..."
Footnote: Why exclude algorithmic refinements? Again from that article: “Designing good quantum algorithms is a very difficult task,” Van den Nest agrees. “I believe this task could be made lighter if we were to arrive at a systematic understanding of the possible ways to move from classical to quantum computing” – in other words, if we had a better grasp of which aspect of quantum physics the advantages ultimately stem from."
I just noticed that link is going be unfamiliar (to me too). So I vetted it just a little. The home page says: "Dr. Franco Nori is a RIKEN Chief Scientist, heading the “Theoretical Quantum Physics Laboratory” at the “Cluster for Pioneering Research” at Riken, Saitama, Japan. He is also at the University of Michigan, Ann Arbor, USA"