The Transmon Qubit: An Artificial Atom in a Microwave Oven

Synopsis

Two-level quantum systems have long been important in atomic physics, especially in studying light-matter interaction and cavity quantum electrodynamics. Recently, quantum information processing has pushed for the creation of these systems in controllable and scalable physical platforms. Superconducting circuits offer one method by enabling quantum behavior to be designed from electrical components. In this presentation, we demonstrate how to build a qubit using a superconducting LC circuit and explain why adding nonlinearity is necessary to achieve a usable qubit. We then present the transmon qubit as a nonlinear superconducting circuit and connect it to a microwave resonator. Finally, we show that the resulting system is formally similar to an atom interacting with a cavity field, linking superconducting circuits to cavity quantum electrodynamics.