研究目的
To develop a high-quality-factor, frequency-tunable microwave resonator using Nb and constriction nano-SQUIDs fabricated with a neon focused ion beam, capable of operating at magnetic fields optimal for spin systems.
研究成果
The study successfully demonstrates Nb-based tunable resonators with high quality factors (up to 1.25e5) and significant frequency tuning (100 MHz), operating resiliently at magnetic fields up to 0.5 mT. The nano-SQUID embedding introduces minimal extra loss, with performance primarily limited by the Nb film quality. These devices are promising for hybrid quantum systems, such as coupling to spin ensembles at high fields.
研究不足
The devices show hysteretic behavior and premature switching due to flux trapping and self-inductance effects. Quality factors degrade with tuning and at higher magnetic fields, limited by film quality and potential vortex formation. Flux focusing complicates field calibration, and losses at low powers are not fully understood.
1：Experimental Design and Method Selection:
The study involves designing and fabricating Nb coplanar resonators with embedded constriction nano-SQUIDs using a neon focused ion beam (Ne FIB) to create weak links. The resonators are characterized for frequency tunability, quality factor, and magnetic field resilience. Theoretical models include Josephson junction behavior and SQUID inductance tuning.
2：Sample Selection and Data Sources:
Two Nb films (chips A and B) are deposited on Si substrates via DC magnetron sputtering. Each chip has a tunable resonator (e.g., ATune, BTune) and a bare resonator for comparison. Data is collected through microwave transmission measurements.
3：List of Experimental Equipment and Materials:
Equipment includes a Ne FIB system, electron-beam lithography setup, reactive-ion etcher, 3He cryostat, Rohde & Schwarz ZNB8 vector network analyzer, superconducting magnet, Keithley 2400 SourceMeter, cryogenic amplifier, and microwave feed lines. Materials include Nb films, Si substrates, resists for lithography, and SF6/Ar gases for etching.
4：Experimental Procedures and Operational Workflow:
Fabrication involves depositing Nb films, patterning resonators and SQUID loops with EBL and reactive-ion etching, narrowing constrictions with Ne FIB milling, and measuring microwave transmission at cryogenic temperatures with applied magnetic fields. Steps include field sweeps and power-dependent measurements.
5：Data Analysis Methods:
Data is analyzed using a circle fit routine to extract resonator parameters (e.g., quality factors, resonant frequencies). Fits to theoretical models (e.g., Eq. (5) for frequency tuning) are performed, and statistical analysis on junction dimensions is conducted.
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