Few corners of the tech industry are as tantalizing or complex as quantum computing. For years, evangelists have promised machines capable of breaking the most impenetrable coded messages, unlocking the secret properties of the physical world and putting supercomputers to shame. But Rigetti Computing, one of the most prominent and well-funded startups in the field, would just like to lower everyone’s expectations. Its challenge: Can it solve even one problem with a quantum computer that a conventional machine cannot?