Progress in the High Coherence 3D SRF Qubit Architecture*

Superconducting radio frequency (SRF) cavities with seconds of coherence coupled with the superconducting transmon qubits to enable quantum operations present a powerful very high coherence platform for quantum computing and sensing - "3D SRF qubits". Long coherence times of SRF cavities allow access to multiple energy levels within the same mode, enabling e.g. the qudit architecture for quantum state encoding and manipulation - with a big decrease in the required hardware/wiring overhead and the potential all-to-all qubit connectivity versus the nearest neighbor in 2D approaches. 3D SRF qubits form a foundation for the devices effort of the Superconducting Quantum Materials and Systems (SQMS) center - one of the five DOE National QIS Research Centers [*]. 

Here we present the succesful integration of Fermilab high Q cavities with Rigetti superconducting qubits, including the coherence times of the resulting 3D SRF qubits and various quantum state manipulations demonstrating the key advantages of the long coherence. We also present further improvements in the coherence of 3D SRF qubits via targeted surface studies and treatments, and discuss the emerging near-term prospects for the 3D SRF qubit-based QPUs capabilities.

[*] https://science.osti.gov/Initiatives/QIS/QIS-Centers