RESUMEN
Intrigued by the discovery of the long lifetime in the α-Ta/Al2O3-based Transmon qubit, researchers recently found α-Ta film is a promising platform for fabricating multi-qubits with long coherence time. To meet the requirements for integrating superconducting quantum circuits, the ideal method is to grow α-Ta film on a silicon substrate compatible with industrial manufacturing. Here we report the α-Ta film sputter-grown on Si (100) with a low-loss superconducting TiNx buffer layer. The α-Ta film with a large growth temperature window has a good crystalline character. The superconducting critical transition temperature (Tc) and residual resistivity ratio (RRR) in the α-Ta film grown at 500 °C are higher than that in the α-Ta film grown at room temperature (RT). These results provide crucial experimental clues toward understanding the connection between the superconductivity and the materials' properties in the α-Ta film and open a new route for producing a high-quality α-Ta film on silicon substrate for future industrial superconducting quantum computers.
RESUMEN
Tantalum and aluminum on sapphire are widely used platforms for qubits of long coherent time. As quantum chips scale up, the number of Josephson junctions on sapphire increases. Thus, both the uniformity and stability of the junctions are crucial to quantum devices, such as scalable superconducting quantum computer circuit, and quantum-limited amplifiers. By optimizing the fabrication process, especially, the conductive layer during the electron beam lithography process, Al/AlOx/Al junctions of sizes ranging from 0.0169 to 0.04 µm2 on sapphire substrates were prepared. The relative standard deviation of room temperature resistances (RN) - [Formula: see text] of these junctions is better than 1.7% on 15 mm × 15 mm chips, and better than 2.66% on 2 inch wafers, which is the highest uniformity on sapphire substrates has been reported. The junctions are robust and stable in resistances as temperature changes. The resistances increase by the ratio of 9.73% relative to RN as the temperature ramp down to 4 K, and restore their initial values in the reverse process as the temperature ramps back to room temperature. After being stored in a nitrogen cabinet for 100 days, the resistance of the junctions changed by1.16% on average. The demonstration of uniform and stable Josephson junctions in large area paves the way for the fabrication of superconducting chip of hundreds of qubits on sapphire substrates.
RESUMEN
Inspired by crystalline lenses in human eyes, liquid lenses have a simple yet elegant working principle, and result in compact optical systems. Recent numerical studies showed that membranes with variable thicknesses could affect the lens profile. However, fabrication and assembly of a liquid lens with an inhomogeneous membrane is difficult. There is also a lack of experimental studies about the changes of a lens profile during deformation. In this paper, we provided a new experimental approach for characterizing the performance of a liquid lens with an inhomogeneous membrane. A 2D axisymmetric lens model was built in finite element analysis software to theoretically study the non-linear deformation behavior of the inhomogeneous membrane. Then we provided a new approach to fabricate inhomogeneous membranes using a pre-machined aluminum mold. An optical coherence tomography (OCT) system was used to dynamically measure the changes of a lens profile without contact. Both simulation and the experiments indicated that the variation of the thickness of the membrane could affect the lens profile in a predictable manner. A negative conic constant was achieved when a plano-concave membrane was adopted in a liquid lens. Larger increments of the thickness of the membrane in the radial direction resulted in a larger contribution of a conic constant to the lens profile. The presented study offers guidance for image-quality analysis and optimization of a liquid-lens-based optical system.