We report high qubit coherence as well as low cross-talk and single-qubit gate errors in a superconducting circuit architecture that promises to be tileable to two-dimensional (2D) lattices of qubits. The architecture integrates an inductively shunted cavity enclosure into a design featuring nongalvanic out-of-plane control wiring and qubits and resonators fabricated on opposing sides of a substrate. The proof-of-principle device features four uncoupled transmon qubits and exhibits average energy relaxation times T ₁ = 149(38) μs, pure echoed dephasing times T _{ϕ, e} = 189(34) μs, and single-qubit gate fidelities F = 99.982(4)% as measured by simultaneous randomized benchmarking. The 3D integrated nature of the control wiring means that qubits will remain addressable as the architecture is tiled to form larger qubit lattices. Band structure simulations are used to predict that the tiled enclosure will still provide a clean electromagnetic environment to enclosed qubits at arbitrary scale.

Using quantum systems with more than two levels, or qudits, can scale the computational space of quantum processors more efficiently than using qubits, which may offer an easier physical implementation for larger Hilbert spaces. However, individual qudits may exhibit larger noise, and algorithms designed for qubits require to be recompiled to qudit algorithms for execution. In this work, we implemented a two-qubit emulator using a 4-level superconducting transmon qudit for variational quantum algorithm applications and analyzed its noise model. The major source of error for the variational algorithm was readout misclassification error and amplitude damping. To improve the accuracy of the results, we applied error-mitigation techniques to reduce the effects of the misclassification and qudit decay event. The final predicted energy value is within the range of chemical accuracy.

This paper presents metal 3D printed wideband bandpass filters based on a deformed elliptical cavity resonator. The resonator can produce a wide stopband response by realising arbitrary real-frequency transmission zero at prescribed frequencies. The design procedure of canonical filtering functions is detailed. Six design examples of bandpass filters are presented to validate the design methodology. Three of the designed filters were metal 3D printed using Selective Laser Melting in AlSi10Mg and commercially pure copper for experimental verification. Copper filter prototypes were printed in one piece and electro-polished to improve the surface finish. Aluminium filters were printed in three different orientations to the wiper to investigate the influence on RF performance. All measured results have a good agreement with simulations. Furthermore, an in-depth review and discussion of Additive Manufacturing techniques for producing complex microwave components and strategies to mitigate the drawbacks of AM are given.

This study presents an original asymmetric stepped‐impedance resonator filter combined with meander coupled‐line structures and enabling the realisation of finite transmission zeros (TZs) and the implementation of multi‐band bandpass filters. The meander coupled sections (MCSs) tune the TZs and resonant frequencies: with higher‐order spurious frequencies cancelled by the TZs, a single wideband with wide stopband from 1.18 to 1.84 GHz is possible. Furthermore, by positioning the finite TZs between the high‐order spurious frequencies and adjusting the coupling strength between resonators, a quint‐wideband filter can be realised, with centre frequencies of 1.19, 4.29, 5.43, 6.97, 9.9 GHz and fractional bandwidths of 31.9, 15.4, 15.8, 4.3, 39.2%, respectively. More importantly, two filters with single/quad‐wideband performance can be realised by tuning the parameters of the MCS, and therefore they can be designed separately by using only one original structure. The triple‐wideband filter is realised with the help of the asymmetric parallel uncoupled microstrip section. These filter structures enjoy the advantage of single/multi‐band versatility, structure reusability and simplicity. The good in‐band and out‐of‐band performance, low loss and simple structure of the proposed single/tri/quint‐wideband filters make them very promising for applications in future multi‐standard wireless communication.

Differentially driven devices represent a highly promising research field for radio frequency (RF), microwave (MW), and millimeter-wave (mmWave) designers and engineers. Designs employing differential signals are essential elements in low-noise fourth-generation (4G) and fifth-generation (5G) communications. Apart from the conventional planar MW components, differential–fed balanced microstrip filters, as promising alternatives, have several advantages, including high common-mode rejection, low unwanted radiation levels, high noise immunity, and wideband harmonic suppression. In this paper, a comprehensive and in-depth review of the existing research on differential-fed microstrip filter designs are presented and discussed with a focus on recent advances in this research and the challenges facing the researchers. A comparison between different design techniques is presented and discussed in detail to provide the researchers with the advantages and disadvantages of each technique that could be of interest to a specific application. Challenges and future developments of balanced microstrip bandpass filters (BPFs) are also presented in this paper. Balanced filters surveyed include recent single-, dual-, tri-, and wide-band BPFs, which employ different design techniques and accomplish different performances for current and future wireless applications.

In this paper, a new class of triple-mode microwave filters is presented. These devices use the degenerate pair of the H E _11δ mode and the single T M _01δ mode in dielectric-loaded cavities with an unloaded Q-factor of 3000-5000 and reasonable spurious-free window. The proposed structure is obtainable in less than one-quarter of the physical volume of equivalent TEM filters. A finite-element method solver for electromagnetic structures (HFSS) is used to study the main properties of this resonator. Fundamental design rules for triple-mode bandpass filters with controllable finite transmission zeros are presented. Design examples of bandpass filters with finite transmission zeros on the high or low or both sides of the passband are demonstrated. Measured results demonstrate excellent performance.