2^50 is the upper bound on the size of the solution space that can be searched by a 50-bit quantum computer. If that same solution space were divided up amongst

2^50 is the upper bound on the size of the solution space that can be searched by a 50-bit quantum computer. If that same solution space were divided up amongst the hundreds of thousands of cores in the world's largest supercomputers, the solution could be found in much less than 1 second, or indeed much less than 1 cycle of any computer, quantum or otherwise. Anyway, whatever "cycle" means in a quantum computer, it would take much more than 1 cycle to search the whole solution space. Assuming your problem is in BQP you still have to iterate until error is within acceptable limits.