Speaker
Description
Superconducting quantum bits (qubits) are regarded as the key technological building blocks for future quantum computers and sensors. One of the primary obstacles to extending qubit performance and in particular coherence times is the presence of photon-absorbing defects, commonly modeled as two-level systems (TLS). Microscopic sources of TLS—such as oxygen vacancies, hydroxyl groups, and amorphized structures—have been identified in dielectric surfaces, interfaces, and Josephson junctions. Thanks to its atomic-scale control of composition and thickness, atomic layer deposition (ALD) offers a powerful approach to address this challenge and mitigate some of these defect mechanisms. ALD is also fully compatible with standard microelectronic fabrication processes and can be readily integrated into the production of two-dimensional superconducting films.
Niobium (Nb) superconducting cavities, widely used in particle accelerators, provide a simpler type of resonator compared to qubits, with the advantage of involving only a single interface—Nb and vacuum. This makes them ideal platforms for investigating how the structure, chemical composition, and thickness of various oxide capping layers affect resonator performance and TLS behavior.
In this work, I will present performance measurements from Nb superconducting resonators coated via ALD with amorphous as well as crystalline films with thicknesses between 2 and 10 nm. Following thermal treatments, these coatings were found to enhance quality factors and coherence times relative to bare niobium with its native oxide. TLS-model fits of RF measurements, combined with surface characterization techniques such as XPS and TEM, enable the extraction of TLS-related properties—including dielectric losses and defect concentrations—in the various capping layers.
These findings offer valuable insight for future technological developments of superconducting resonators operating in the quantum regime, including qubit architectures