Towards practical quantum computers: transmon qubit with a lifetime approaching 0.5 milliseconds

Here we report a breakthrough in the fabrication of a long lifetime transmon qubit. We use tantalum films as the base superconductor. By using a dry etching process, we obtained transmon qubits with a best T1 lifetime of 503 μs. As a comparison, we also fabricated transmon qubits with other popular materials, including niobium and aluminum, under the same design and fabrication processes. After characterizing their coherence properties, we found that qubits prepared with tantalum films have the best performance. Since the dry etching process is stable and highly anisotropic, it is much more suitable for fabricating complex scalable quantum circuits, when compared to wet etching. As a result, the current breakthrough indicates that the dry etching process of tantalum film is a promising approach to fabricate medium- or large-scale superconducting quantum circuits with a much longer lifetime, meeting the requirements for building practical quantum computers.

The SU-8 spin-coating on silicon nanowires formed by cryogenic dry etching

Arrays of vertically aligned silicon nanowires were fabricated by cryogenic dry etching. The post-processing technology was developed to full coating of arrays of NWs by SU-8 and release the top side of SiNWs. The Schottky diodes were fabricated on arrays of SiNWs with and without SU-8 by gold evaporation. The cryogenic dry etching leads to defect formation with Ea=0.28 eV and concentration lower 5⋅1012 cm−3 in near-surface area in silicon, and no defect are detected in bulk silicon. However, oxygen plasma treatment used to release top side of SiNWs leads to increase of its concentration by two order and formation of defect with Ea=0.39 eV, σ = 1⋅10−16 cm2 and a concentration of 5⋅1014 cm−3 in a bulk of SiNWs deeper than 1 μm.

Specific features of the formation of optical waveguides, contact pads and electrical interconnections on lithium tantalate substrates

The article considers the formation of titanium channel optical waveguides in LiTaO3 substrates. These structures were obtained by dry etching of grooves in SF6 plasma and magnetron sputtering of titanium film. After that, waveguides were formed by plasma etching using photoresist as mask. Technological features and modes of microstructure production are described. Al contact pads were produced by magnetron sputtering thin metal films on LiTaO3. Aluminum wires were ultrasonically bonded to Al contact pads using Delvotec 5630. The developed technology of formation of contact pads and bonding modes made it possible to obtain a bonded joint with a bond strength of 23-25 Gs.