As a result, to show performance advantages for quantum computers, we have to build an (actual) quantum computer that does something a classical computer can’t. Unfortunately, reliable quantum computers were, until recently, limited to just a few quantum bits (qubits). Because of this bit scarcity, any problem solvable on a quantum computer could be solved much faster on a classical computer, simply because the problems were so small.
One solution, of course, is to make quantum computers with a larger number of qubits so that they can handle larger problems. Once that is achieved, quantum computers should be faster than classical computers — provided those tricky mathematical proofs hold for non-ideal quantum computers.Putting together a general-purpose quantum computer with lots of qubits is easier said than done. Putting together a computer that can solve a single problem, however, is easier than building a general-purpose computer. Such a particular quantum computer allows engineers to show that a quantum computer is faster than a classical computer onthis single problem, while allowing them to avoid the task of producing a generally useful computer . The ray of hope this success would provide might reassure people who control budgets, providing researchers with the funding necessary to turn a special-purpose (that is, not very useful) quantum computer into a general-purpose (that is, very useful!) quantum computer.