That gap is not likely to be closed anytime soon. There is a tremendous gap between the rudimentary but very hard experiments that have been carried out with a few qubits and the extremely developed quantum-computing theory, which relies on manipulating thousands to millions of qubits to calculate anything useful. > All these problems, as well as a few others I’ve not mentioned here, raise serious doubts about the future of quantum computing. The proponents have grown older and less zealous, while the younger generation seeks something completely new and more likely to succeed. What’s more, by that time all the tenured faculty positions in the field are already occupied. After a certain period, too many unfulfilled promises have been made, and anyone who has been following the topic starts to get annoyed by further announcements of impending breakthroughs. That’s because a few decades is the maximum lifetime of any big bubble in technology or science. > I believe that, appearances to the contrary, the quantum-computing fervor is nearing its end. Unlike the transistor revolution, there is no clear path forward upon which we might improve these initial results. The levels of engineering effort required, and the orders of magnitude separating what has been realized by those efforts and what is required by theory, lends itself towards narratives of impossibility. We have managed to perform simultaneous gate operations on two. In the error-correcting model, we must perform simultaneous gate operations on at least thousands of qubits. We have, with superconducting circuits operating at 20 milli-kelvin, managed to corral 53 qubits into a circuit.

You need on the order of millions of qubits for quantum error correction algorithms to work.

Big quantum error after all