Samsung Advanced Institute of Technology

Multimode cavity quantum electrodynamics (QED)|where a two level system interacts simultaneously with many cavity modes|provides a versatile framework for quantum information processing and quantum optics. Due to the combination of long coherence times and large interaction strengths, one of the leading experimental platforms for cavity QED involves coupling a superconducting circuit to a 3D microwave cavity, a eld known as circuit QED (cQED). In this work, we realize a 3D multimode circuit QED system with single photon lifetimes of 2 ms and cooperativities of 0:5 ？？ 1:5  109 across 9 modes of a novel seamless cavity. We demonstrate a variety of protocols
for universal single-mode quantum control applicable across all cavity modes, using only a single drive line. We achieve this by developing a straightforward ute method for creating monolithic superconducting microwave cavities that reduces loss while simultaneously allowing control of the mode spectrum and mode-qubit interaction. We highlight the exibility and ease of implementation
of this technique by using it to fabricate a variety of 3D cavity geometries, providing a template for engineering multimode quantum systems with exceptionally low dissipation. This device is an important step towards realizing hardware ecient random access quantum memories and processors, and for exploring quantum many-body physics with photons.