Building a 3D quantum processing unit using a high-coherence SRF cavity*

TESLA-shaped superconducting RF (SRF) cavities have been demonstrated to offer photon relaxation times of the order of seconds in the quantum regime [1]. As a result, TESLA cavities coupled to transmon ancilla qubits are promising candidates for 3D quantum processing unit (QPU) and quantum memory. In this talk, we introduce a novel QPU design based on TESLA cavity aimed at maintaining a large quality factor. We achieve this by careful engineering of the package geometry that minimizes the participation of the fundamental mode in different loss channels. This new design allows for the separate control of the high-Q modes and the over-coupled low-Q modes without compromising the functionality of each mode. We further utilize a multimode stripline resonator [2] to characterize the loss channels of the system for predicting and optimizing the design. We report on the long coherence of the storage mode and show how it facilitates high-fidelity operations.