What is a quantum computer, and how do we build one?

Abstract

The DiVincenzo criteria for implementing a quantum computer have been seminal in focussing both experimental and theoretical research in quantum information processing. These criteria were formulated specifically for the circuit model of quantum computing. However, several new models for quantum computing (paradigms) have been proposed that do not seem to fit the criteria well. The question is therefore what are the general criteria for implementing quantum computers. To this end, a formal operational definition of a quantum computer is introduced. It is then shown that according to this definition a device is a quantum computer if it obeys the following criteria: Any quantum computer must consist of a quantum memory, with additional structure that (1) facilitates a controlled quantum evolution of the quantum memory; (2) includes a method for information theoretic cooling of the memory; and (3) provides a readout mechanism for subsets of the quantum memory. The criteria are met when the device is scalable and operates fault-tolerantly. We discuss various existing quantum computing paradigms, and how they fit within this framework. Finally, we present a decision tree for selecting an avenue towards building a quantum computer. This is intended to help experimentalists determine the most natural paradigm given a particular physical implementation.

From molecular control to quantum technology with the dynamic Stark effect

“…One experimental challenge in building these devices is finding suitable quantum systems and to interact with them in an efficient and precise manner. Various systems have been investigated including propagating photons, 38,39 ions, 40 nuclear spins, 41 high Q-cavities and others. 42 All have appealing features and challenges.…”