“The watershed moment with quantum computer technology will be when a quantum computer — a universal quantum computer — exceeds about 100 to 200 qubits,” according to Oxford University theoretical physicist David Deutsch. In practice, “that probably means several hundred, or perhaps 1,000 or more, physical qubits.”

He said the most important applications of quantum computing in the future are likely to be a computer simulation of quantum systems, quantum cryptography, mathematical operations such as algorithmic search, and design of nanotechnological devices.