Integrated plasmonics is advancing rapidly, enabling a wide range of functionalities to be incorporated onto a single chip. Applications span information processing, computation, quantum sensing, and dark-matter detection. This progress has driven the development of integrated non-reciprocal devices, which are essential for preventing unwanted feedback that can degrade system performance. While non-reciprocal devices have been realized in edge magnetoplasmon materials via classical interference effects, their operation is often limited by the input power range. Here, we demonstrate that topological circulators utilizing asymmetric coupling offer improved input power range, isolation, and insertion loss. In this configuration, we demonstrate the coupling between a chiral edge magnetoplasmonic resonator and a pair of LC resonators is well described by an effective non-Hermitian two-site Hatano-Nelson model with asymmetric directional couplings, resulting in nonreciprocal behavior. The coherent photon-plasmon interaction enables a circulator with up to 50 dB of isolation across a broad range of excitation power. These results suggest that magnetic topological insulators provide a promising platform for realizing asymmetric non-Hermitian couplings at radio frequencies and for exploring regimes of strong directional suppression and possible exceptional-point physics. More broadly, they highlight the potential of topological-material-based microwave devices for future integration with superconducting quantum information platforms.

Superconducting microwave resonators are used in many low-power applications, such as the study of two-level system loss in superconducting quantum devices. Fano asymmetry, characterized by a nonzero asymmetry angle in the diameter correction method, results from the coupling schemes used to measure these devices, including the commonly used hanger method. is an additional fitting parameter which contains no physically interesting information and can obscure device parameters of interest. The T-junction symmetry nominally present in these resonator devices provides an avenue for the elimination of Fano asymmetry using calibrated measurement. We show that the eigenvalue associated with the common mode excitation of the resonator is an effective reflection mode (ERM) which has no Fano asymmetry. Our analysis reveals the cause of Fano asymmetry as interference between common and differential modes. Practically, we obtain the ERM from a linear combination of calibrated reflection and transmission measurements. We utilize a three-dimensional aluminum cavity to experimentally demonstrate the validity and flexibility of this model. To extend the usefulness of this symmetry analysis, we apply perturbation theory to recover the ERM in a multiplexed coplanar waveguide resonator device and experimentally demonstrate quantitative agreement in the extracted Q-1 i between hanger mode and ERM measurements. We observe a fivefold reduction in uncertainty from the ERM compared to the standard hanger mode at the lowest measured power, -160 dBm delivered to the device. This method could facilitate an increase in throughput of low-power superconducting resonator measurements by up to a factor of 25, as well as allow the extraction of critical parameters from otherwise unfittable device data.

Superconducting niobium (Nb) thin films have recently attracted significant attention due to their utility for quantum information technologies. In the processing of Nb thin films, fluoride-based chemical etchants are commonly used to remove surface oxides that are known to affect superconducting quantum devices adversely. However, these same etchants can also introduce hydrogen to form Nb hydrides, potentially negatively impacting microwave loss performance. Here, comprehensive materials characterization of Nb hydrides formed in Nb thin films as a function of fluoride chemical treatments is presented. In particular, secondary-ion mass spectrometry, X-ray scattering, and transmission electron microscopy reveal the spatial distribution and phase transformation of Nb hydrides. The rate of hydride formation is determined by the fluoride solution acidity and the etch rate of Nb2O5, which acts as a diffusion barrier for hydrogen into Nb. The resulting Nb hydrides are detrimental to Nb superconducting properties and lead to increased power-independent microwave loss in coplanar waveguide resonators. However, Nb hydrides do not correlate with two-level system loss or device aging mechanisms. Overall, this work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices. This study provides comprehensive materials characterization of niobium (Nb) hydrides formed in Nb thin films as a function of fluoride chemical treatments that are commonly employed in the fabrication of superconducting qubits. This work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices. image

In recent years, the implementation of thin-film Ta has led to improved coherence times in superconducting circuits. Efforts to further optimize this materials set have become a focus of the subfield of materials for superconducting quantum computing. It has been previously hypothesized that grain size could be correlated with device performance. In this work, we perform a comparative grain size experiment with α-Ta on c axis sapphire. Our evaluation methods include both room-temperature chemical and structural characterization and cryogenic microwave measurements, and we report no statistical difference in device performance between smaller- and larger-grain-size devices with grain sizes of 924 and 1700 nm2, respectively. These findings suggest that grain size is not correlated with loss in the parameter regime of interest for Ta grown on c axis sapphire, narrowing the parameter space for optimization of this materials set.

Adoption of fast, parametric coupling elements has improved the performance of superconducting qubits, enabling recent demonstrations of quantum advantage in randomized sampling problems. The development of low loss, high contrast couplers is critical for scaling up these systems. We present a blueprint for a gate-tunable coupler realized with a two-dimensional electron gas in an InAs/InGaAs heterostructure. Rigorous numerical simulations of the semiconductor and high frequency electromagnetic behavior of the coupler and microwave circuitry yield an on/off ratio of more than one order of magnitude. We give an estimate of the dielectric-limited loss from the inclusion of the coupler in a two qubit system, with coupler coherences ranging from a few to tens of microseconds.

Superconducting qubits have matured from platforms demonstrating and manipulating macroscopic coherent quantum states to realizing exotic quantum states, running surface error correction codes, and single photon detection to name a few recent milestones. This article will review the fundamentals of circuit QED related to the design and simulation of superconducting qubits.

Superconducting qubits and circuit quantum electrodynamics have enabled design of solid state sources of quantum information. The performance of these devices has scaled exponentially over the last fifteen years, in terms of their energy relaxation and dephasing times, drawing interest from adjacent communities including the Axion Dark Matter Experiment (ADMX). Recently, superconducting qubits have been targeted for use as single photon detectors in the ADMX high frequency experiment, ADMX-HF [16]. The goal of this article is to give members of the ADMX community an introduction to some of the models used to analyze and design superconducting qubits. This review is not an exhaustive coverage of the field, but it aims to guide the reader to relevant literature and analysis techniques that closely follow experiment.

Investigations into the microwave surface impedance of superconducting resonators have led to the development of single photon counters that rely on kinetic inductance for their operation, while concurrent progress in additive manufacturing, “3D printing,” opens up a previously inaccessible design space for waveguide resonators. In this manuscript, we present results from the synthesis of these two technologies in a titanium, aluminum, vanadium (Ti-6Al-4V) superconducting radio frequency resonator which exploits a design unattainable through conventional fabrication means. We find that Ti-6Al-4V has two distinct superconducting transition temperatures observable in heat capacity measurements. The higher transition temperature is in agreement with DC resistance measurements, while the lower transition temperature, not previously known in the literature, is consistent with the observed temperature dependence of the superconducting microwave surface impedance. From the surface reactance, we extract a London penetration depth of 8 ± 3 μm—roughly an order of magnitude larger than other titanium alloys and several orders of magnitude larger than other conventional elemental superconductors.

Heterogeneous systems consisting of multi-core CPUs, Graphics Processing Units (GPUs) and many-core accelerators have gained widespread use by application developers and data-center platform developers. Modern day heterogeneous systems have evolved to include advanced hardware and software features to support a spectrum of application patterns. Heterogeneous programming frameworks such as CUDA, OpenCL, and OpenACC have all introduced new interfaces to enable developers to utilize new features on these platforms. In emerging applications, performance optimization is not only limited to effectively exploiting data-level parallelism, but includes leveraging new degrees of concurrency and parallelism to accelerate the entire application. To aid hardware architects and application developers in effectively tuning performance on GPUs, we have developed the NUPAR benchmark suite. The NUPAR applications belong to a number of different scientific and commercial computing domains. These benchmarks exhibit a range of GPU computing characteristics that consider memory-bandwidth limitations, device occupancy and resource utilization, synchronization latency and device-specific compute optimizations. The NUPAR applications are specifically designed to stress new hardware and software features that include: nested parallelism, concurrent kernel execution, shared host-device memory and new instructions for precise computation and data movement. In this paper, we focus our discussion on applications developed in CUDA and OpenCL, and focus on high-end server class GPUs. We describe these benchmarks and evaluate their interaction with different architectural features on a GPU. Our evaluation examines the behavior of the advanced hardware features on recently-released GPU architectures.