Encapsulating Ta films with Pt for novel Josephson junctions and quantum information applications

The coherence time of superconducting qubits limits the scale and complexity of quantum circuits. Tantalum-based transmon qubits have demonstrated that coherence times can exceed 0.3 ms^[1]. However, the amorphous oxide surface of the Ta hosts TLS losses and introduces dielectric losses that could limit qubit lifetimes. In addition, this insulating oxide layer poses a challenge in creating ohmic contact to the Ta layer limiting the potential kinds of junctions made. We demonstrate a technique to encapsulate the Ta films with a Pt layer to eliminate the Ta oxide growth. By growing a thin uniform layer of Pt in situ on top of the Ta, we will show heavily diminished oxide peaks seen through XPS. This enables us to create unique novel Josephson junctions using the Ta films and other insulating barriers like van der Waals heterostructures such as hexagonal Boron Nitride. We will demonstrate some results using these films in superconducting quantum circuits, such as resonators and JJ-based circuits.