Dielectric Loss from Josephson Junctions in Superconducting Qubits

Superconducting qubits are a leading platform for realizing fault-tolerant quantum computation and have enabled demonstrations of both quantum error correction and quantum simulation. The lifetimes of current superconducting qubits are limited by dielectric loss that is orders of magnitude higher than would be expected from the bulk properties of the constituent materials, suggesting uncontrolled interfaces may be limiting their performance. Recently, tantalum (Ta) has been shown to be a promising material platform for superconducting qubits, and it is believed that its promise is related to both its stoichiometric oxide and chemical robustness. Additional studies of Ta superconducting resonators suggest that dielectric loss from interfaces and bulk materials are comparable for the longest-lived devices, meaning both dielectric loss sources must be addressed if further improvements in device performance are to be achieved. However, qubits based on tantalum still utilize aluminum josephson junctions, which has been suggested to be a dominant source of dielectric loss. Here, we study the dependence of transmon lifetime on the size of the junction leads in order to quantify the contribution of aluminum oxide to dielectric loss in superconducting qubits.