Spatial addressing of qubits in a dispersive waveguide

Waveguide quantum electrodynamics—the study of atomic systems interacting with propagating electromagnetic fields—is a powerful platform for understanding the complex interplay between light and matter. Qubit control is an indispensable tool in this field, and most experiments thus far have used narrowband control pulses to interact with qubits at specific frequencies. Dynamics can change significantly with fast, broadband pulses, since waveguide properties such as dispersion affect the pulse evolution and its impact on the qubit. Here we use dispersion to achieve spatial addressing of superconducting qubits separated by a subwavelength distance within a microwave waveguide. This approach relies on a self-focusing effect to create a position-dependent interaction between a chirped pulse and an individual qubit. This method emphasizes the importance of dispersion in the design and analysis of quantum experiments, and offers avenues for the rapid control of quantum states.