Reproducibility of Al/AlOx/Al Josephson junctions is a challenge for scaling up superconducting quantum processors. The frequency uncertainty of the transmon qubits arising from the fabrication process is attributed to deviations in the Josephson junction microstructure and electrical properties. Here, we present a solution for this problem using the post-fabrication Josephson junction thermal annealing process. The developed thermal post-exposure method allows not only to increase the junction resistance by 175%, but also to decrease by 60% with a step of 10% in Rn, which opens up new possibilities for tuning the frequency of qubits. The resistance is shown to be strongly temperature dependent, and is weakly dependent on the holding time. The linear dimensions of the electrodes and the sidewalls contribution to the total JJ area also have a significant impact on the final resistance after annealing. Finally, a theoretical model of the structure modification in a tunnel barrier with changes in oxygen concentration gradient is proposed. The proposed thermal annealing approach can be used to form stable and reproducible tunnel barriers and scalable frequency trimming for widely used fixed-frequency transmon qubits.

Anapole electrodynamics is now a rapidly developing area of nonradiating and invisible systems like meta- materials, nanoparticles, and even toroidal optical transitions in hydrogenlike atoms from microwaves to optics. The main advantages are demonstrated strong localized near fields and an extremely high Q factor due to the absence of radiating losses. In this paper, we expand the field of anapole electrodynamics to the quantum area and demonstrate the anharmonicity of a superconducting meta-atom with an embedded Josephson junction. The maximum dimension of meta-atoms is 6 mm, and it works in the microwave range. The microwave single- and two-tone spectroscopic measurements in a dilution cryostat at 20 mK demonstrate three transition energy levels: single-photon and two-photon transitions. Moreover, we obtain an anharmonicity of 540 kHz, which is very close to 500 kHz obtained in simulations. We show that the anapole meta-atoms are promising candidates for giant qubits for quantum computing applications.

Dielectric losses are one of the key factors limiting the coherence of superconducting qubits. The impact of materials and fabrication steps on dielectric losses can be evaluated using coplanar waveguide (CPW) microwave resonators. Here, we report on superconducting CPW microwave resonators with internal quality factors systematically exceeding 5 × 10 6 at high powers and 2 × 10 6 (with the best value of 4.4 × 10 6 ) at low power. Such performance is demonstrated for 100-nm-thick aluminum resonators with 7–10.5 um center trace on high-resistivity silicon substrates commonly used in Josephson-junction based quantum circuit. We investigate internal quality factors of the resonators with both dry and wet aluminum etching, as well as deep and isotropic reactive ion etching of silicon substrate. Josephson junction compatible CPW resonators fabrication process with both airbridges and silicon substrate etching is proposed. Finally, we demonstrate the effect of airbridges’ positions and extra process steps on the overall dielectric losses. The best quality factors are obtained for the wet etched aluminum resonators and isotropically removed substrate with the proposed ultrasonic metal edge microcutting.

The most commonly used physical realization of superconducting qubits for quantum circuits is a transmon. There are a number of superconducting quantum circuits applications, where Josephson junction critical current reproducibility over a chip is crucial. Here, we report on a robust chip scale $Al/AlO_x/Al$ junctions fabrication method due to comprehensive study of shadow evaporation and oxidation steps. We experimentally demonstrate the evidence of optimal Josephson junction electrodes thickness, deposition rate and deposition angle, which ensure minimal electrode surface and line edge roughness. The influence of oxidation method, pressure and time on critical current reproducibility is determined. With the proposed method we demonstrate $Al/AlO_x/Al$ junction fabrication with the critical current variation ($\sigma/I_c$) less than 3.9% (from $150\times200$ to $150\times600$ $nm^2$ area) and 7.7% (for $100\times100$ $nm^2$ area) over $20\times20$ $mm^2$ chip. Finally, we fabricate separately three $5\times10$ $mm^2$ chips with 18 transmon qubits (near 4.3 GHz frequency) showing less than 1.9% frequency variation between qubit on different chips. The proposed approach and optimization criteria can be utilized for a robust wafer-scale superconducting qubit circuits fabrication.

Представлены результаты исследований процесса осаждения пленок толщиной менее 100 нм методом электронно-лучевого испарения на специальном вакуумном технологическом оборудовании. Приведены результаты расчета величины энергомассопереноса для получения пленок ITO, Ag и Al с заданной структурой, однородностью состава и шероховатостью

Study results of thin film with thickness less than 50 nm deposition by means of electron beam evaporation on special vacuum coaters were represented. Calculation results of energy and mass carry magnitude for ITO, Ag and Al thin films deposition with preset of structure and composition homogeneity and roughness were shown.

In this work, we irradiate a superconducting artificial molecule composed of two coupled tunable transmons with microwave light while monitoring its state via joint dispersive readout. Performing high-power spectroscopy, we observe and identify a variety of single- and multiphoton transitions. We also find that at certain fluxes, the measured spectrum of the system deviates significantly from the solution of the stationary Schrodinger equation with no driving. We reproduce these unusual spectral features by solving numerically the full master equation for a steady state and attribute them to an Autler-Townes-like effect in which a single tone is simultaneously dressing the system and probing the transitions between new eigenstates. We show that it is possible to find analytically the exact frequencies at which the satellite spectral lines appear by solving self-consistent equations in the rotating frame. Our approach agrees well with both the experiment and the numerical simulation.

The spectral and temporal characteristics of a fluxonium qubit coupled to a coplanar resonator on a chip have been experimentally studied. The system has been implemented as a planar integral electric circuit, where the fluxonium qubit itself consists of a tunnel Josephson junction with a small area shunted by a high inductance of a series of Josephson junctions with larger areas. To analyze the experimental data, an extended model of the fluxonium qubit capacitively coupled to the resonator has been proposed, and the structure of the energy levels has been obtained by full diagonalization of the Hamiltonian of the system. Numerical predictions of the model allow interpreting the results of two-tone spectroscopy obtained at various external magnetic fluxes in a wide frequency range.