Quantum computing: what is it and how far along are we?

Abstract: Imagine if the act of looking at an object caused it to move – or imagine you had a pair of dice that always rolled doubles, but of different numbers each roll. These counterintuitive phenomena are commonplace in the realm of quantum mechanics, which describes systems that are generally very small, very cold, and/or very isolated from the rest of the world. Over the past 40 years, scientists have developed ideas for harnessing the strange features of quantum mechanics to build “quantum computers”, machines where information storage and computation is carried out by objects that behave quantum mechanically. A large-scale quantum computer would in principle be able to perform certain kinds of computations that would be impossible on even the largest classical (i.e. non-quantum) supercomputers. I will describe some of the basics of quantum mechanics and quantum computing, including why it is so technically challenging to build a “useful” large-scale quantum computer. I will also give some perspective on where things stand in the quest for quantum computers that will provide an advantage over existing computing technology.