Increasing the number of qubits doesn't help unless the gate fidelities and coherence times also improve. Otherwise, the system quickly becomes a very expensive

Increasing the number of qubits doesn't help unless the gate fidelities and coherence times also improve. Otherwise, the system quickly becomes a very expensive random number generator. In transmon qubit systems, I haven't seen much progress in these metrics over the last couple of years. IBM keep adding more qubits to their chips, but they don't seem to be able to actually use them. After almost thirty years of development, ion traps have now reached a few ten qubits with reasonable fidelities. However, this requires shuttling the ions between trapping zones which is enormously slow (many milliseconds per gate). And scaling this to hundreds of thousands of qubits is a completely open question (none of the current techniques will work).