Since the 1990s, evidence has been growing that quantum computers should be able to solve a range of particularly complex computational problems, with applications in everything from supply chain ...

If it holds up, it will solve in one fell swoop a number of related problems in pure mathematics, quantum mechanics and a branch of computer science known as complexity theory.

Hypothetical devices that can quickly and accurately answer questions have become a powerful tool in computational complexity theory.

But is there a simpler way? Questions like this one, about the most efficient way to solve problems, are at the heart of the branch of computer science known as computational complexity theory.

Regan, 65, has made this question his life’s work, in a field of computer science known as complexity theory.