arXiv subjects

Nick Du

Publications and source records attributed to Nick Du.

3 recordsLinked to original sources

arXiv2026

Characterization of a hybrid superconducting RF cavity for use in axion searches

We report on the development of a hybrid superconducting radio-frequency (SRF) cavity for axion haloscopes. The Axion Dark Matter eXperiment (ADMX) Sidecar has been a program of ADMX for testing technologies with the potential for improving high frequency cavity haloscopes in the 4-6 GHz range. A replica of the Sidecar cavity, an aluminum clamshell microwave resonator loaded with a niobium tuning rod coated with Nb3Sn, was characterized in a dilution fridge through its critical temperature transitions down to 25 mK and through magnetic fields up to 6 T. The quality factor of five resonant modes of the cavity system were monitored throughout the process, including the TM010 mode used in axion searches. Distinct superconducting transitions were observed near the expected critical temperatures of Nb3Sn, pure niobium, and aluminum. The TM010 mode exhibited a factors of improvement in quality factor of 1.86 and 2.87 through the two niobium transitions, which implied the rod had a zero-field surface resistance of roughly 79% that of copper at cryogenic temperatures. Magnet tests showed a distinct superconducting transition for aluminum, and gradual degradation of quality factor expected for Nb3Sn in a mixed superconducting state. This hybrid resonator design has been integrated in the ADMX insert for performing an axion-like particle search.

physics.ins-det↗

arXiv2026

Probing Quantum Anomalous Hall Transport Under Microwave Irradiation Using a Topological Circulator

Edge magnetoplasmons (EMPs) provide a platform for probing chiral charge dynamics and nonreciprocal microwave transport in topological quantum materials. However, detecting small perturbations to EMP propagation remains challenging because their signatures in conventional microwave scattering measurements can be weak. Here, we investigate microwave-photon-induced perturbations of EMP transport using a quantum anomalous Hall topological circulator. Pump--probe measurements reveal a strongly frequency-selective response: while microwave irradiation substantially modifies the EMP transmission at several pump frequencies, the transmission remains nearly unchanged at selected frequencies, including 4 and 7 GHz. We further exploit the non-Hermitian mode hybridization of the coupled EMP-resonator system to probe the response near an exceptional point (EP). The pump-induced change in transmission magnitude near the EP is approximately twice that observed away from the EP, demonstrating an enhanced microwave response to perturbations. These results reveal the interplay among chiral EMP transport, microwave-photon-induced perturbations, and non-Hermitian dynamics, and demonstrate the potential of topological circulators as a promising platform for enhanced microwave spectroscopy and sensing.

quant-ph↗

arXiv2026

Circulators Based on Coupled Quantum Anomalous Hall Insulators and Resonators

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.

quant-ph↗