arXiv subjects

Mingqi Ge

Publications and source records attributed to Mingqi Ge.

4 recordsLinked to original sources

arXiv2026

Design optimization, commissioning, and uncertainty analysis of the quadrupole resonator system at Jefferson Lab for SRF material characterization

A quadrupole resonator (QPR) provides a sample-based platform for characterizing materials for superconducting radio-frequency (SRF) applications under controlled field, frequency, and temperature conditions. This paper presents the design optimization, commissioning, and validation of the Jefferson Lab QPR system, including a quantitative assessment of measurement uncertainty. The resonator geometry was re-optimized from the CERN version-II design to improve quadrupole-mode separation and enable four usable modes at 400, 806, 1221, and 1640 MHz. The measurement system combines self-excited-loop RF operation, cable-loss-corrected power calibration, decay-based external-Q calibration, and RF-DC thermal-substitution calorimetry to determine the peak surface magnetic field Bpk and sample surface resistance Rs. Commissioning measurements on bulk Nb and Nb3Sn-Ta-Cu samples validated the system response over a broad range of frequency, temperature, and RF field. The extracted superconducting energy-gap parameters are consistent with the reported values for Nb and Nb3Sn, as well as with those obtained from single-cell cavity measurements. The commissioned system operates from 1.8 K to near the superconducting transition temperature of the sample, with accessible Bpk values from approximately 5 mT to a sample- and temperature-dependent heater-power-budget limit; a maximum field of 60 mT was demonstrated for bulk Nb at 400 MHz and 4 K. The combined relative standard uncertainties are 8.3% for Bpk and below 18% for Rs when r = PDC2/PDC1 is less than 0.9. The worst-case Bpk resolution at the 95% confidence level is approximately 1.35 mT, while the Rs resolution is below 1 nOhm at 10 mT and 2 K. These results establish the JLab QPR as a calibrated, multi-frequency platform with quantified measurement uncertainty for SRF material characterization.

physics.acc-ph↗

arXiv2026

RF-Budgeted Frame Compilation for Frequency-Multiplexed Superconducting-Qubit Control Using Qubit-Control Identity Records and a Circuit-Informed RFSoC Model

Frequency-multiplexed superconducting-qubit control requires more than carrier assignment: the RF budget of a shared source can perturb multi-qubit rotations through finite bandwidth, crest factor, clipping, quantization, jitter, spurs, compression, crosstalk, and leakage. We present an RF-budgeted frame-compilation and validation workflow that combines qubit-control identity (QID) records, a MATLAB/Simulink-based circuit-informed RFSoC source-chain model, QuTiP qutrit dynamics, and Qiskit-derived algorithm workloads. QID records encode qubit-specific computational and leakage transition frequencies, pulse parameters, and drive-scale calibration, while the RF-chain profile and effective crosstalk-coupling matrix are provided as separate compiler inputs. Candidate multitone RF frames are scheduled under RF-budget constraints, propagated through the RFSoC model, decoded into computational and leakage transition frames, and evaluated in QuTiP for rotation error, leakage-aware fidelity, computational-subspace survival, and transient leakage. The studies progress from single-qutrit pulse closure to pairwise coexistence, multitone RF-frame capacity, and Bernstein-Vazirani (BV) and QAOA microwave layers extracted from Qiskit circuits. The simulations show that longer pulses improve per-frame aggregation but do not necessarily minimize time-normalized layer cost; clustered frequency maps, larger rotations, and multitone leakage stacking tighten closure. Under the nominal RF budget, a Qiskit-derived 12-qubit BV -Y90 layer closes in three validated four-tone frames at 240 ns, while QAOA mixer partitions vary with rotation angle and pulse duration. All reported results are model-based, decoherence-free simulation diagnostics rather than measured hardware fidelities or wiring-reduction claims.

quant-ph↗

arXiv2023

Electrochemical Polishing of Chemical Vapor Deposited Niobium Thin Films

Combining chemical vapor deposition (CVD) with electrochemical polish (EP) operations is a promising route to producing performance-capable superconducting films for use in the fabrication of cost-effective components for superconducting radiofrequency (SRF) particle accelerators and superconducting quantum computers. The post-deposition EP process enables a critically necessary reduction in surface roughness of niobium thin films to promote optimal superconducting surface conditions. In this work, surface morphology, roughness, and crystal orientation of the CVD-grown and EP-polished niobium films were investigated. The grain growth and polishing mechanisms were analyzed. The CVD films were found to comprise steps, kinks, and pyramidal features, resulting in undesirable large peak-to-valley distances. The electrochemical polish was demonstrated to significantly diminish the height of pyramids and effectively minimize the overall surface roughness. In contrast to buffered chemical polishing (BCP), EP results showed a probable dependence on crystal orientation, suggesting this process was influenced by locally enhanced current density and thickness variations of oxide dielectrics. These understandings identify the EP principles tied to CVD-grown Nb films that allow further refinement of surface profiles for film-based SRF applications

cond-mat.mtrl-sci↗

arXiv2014

Nitrogen-Doped 9-Cell Cavity Performance in a Test Cryomodule for LCLS-II

The superconducting RF linac for LCLS-II calls for 1.3 GHz 9-cell cavities with an average intrinsic quality factor Q0 of 2.7x10^10 at 2 K and 16 MV/m accelerating gradient. Two niobium 9-cell cavities, prepared with nitrogen-doping at Fermilab, were assembled into the Cornell Horizontal Test Cryomodule (HTC) to test cavity performance in a cryomodule that is very similar to a full LCLS-II cryomodule. The cavities met LCLS-II specifications with an average quench field of 17 MV/m and an average Q0 of 3x10^10. The sensitivity of the cavities' residual resistance to ambient magnetic field was determined to be 0.5 nOhm/mG during fast cool down. In two cool downs, a heater attached to one of the cavity beam tubes was used to induce large horizontal temperature gradients. Here we report on the results of these first tests of nitrogen-doped cavities in cryomodule, which provide critical information for the LCLS-II project.

physics.acc-ph↗