Superconducting metamaterials for waveguide quantum electrodynamics

TL;DR

This paper demonstrates how superconducting metamaterials can be used to control quantum emitter interactions and spontaneous emission in waveguide quantum electrodynamics, revealing enhanced and inhibited emission effects near band edges.

Contribution

It introduces a superconducting metamaterial with deep sub-wavelength lattice constant to study and manipulate waveguide QED phenomena, including Lamb shift and spontaneous emission control.

Findings

Observation of a 10 MHz Lamb shift near a band edge.

24-fold enhancement of qubit lifetime at the band edge.

Selective control of spontaneous emission for different transmon transitions.

Abstract

The embedding of tunable quantum emitters in a photonic bandgap structure enables the control of dissipative and dispersive interactions between emitters and their photonic bath. Operation in the transmission band, outside the gap, allows for studying waveguide quantum electrodynamics in the slow-light regime. Alternatively, tuning the emitter into the bandgap results in finite range emitter-emitter interactions via bound photonic states. Here we couple a transmon qubit to a superconducting metamaterial with a deep sub-wavelength lattice constant ($\lambda/60$). The metamaterial is formed by periodically loading a transmission line with compact, low loss, low disorder lumped element microwave resonators. We probe the coherent and dissipative dynamics of the system by measuring the Lamb shift and the change in the lifetime of the transmon qubit. Tuning the qubit frequency in the vicinity of a band-edge with a group index of $n_g = 450$, we observe an anomalous Lamb shift of 10 MHz accompanied by a 24-fold enhancement in the qubit lifetime. In addition, we demonstrate selective enhancement and inhibition of spontaneous emission of different transmon transitions, which provide simultaneous access to long-lived metastable qubit states and states strongly coupled to propagating waveguide modes.