研究目的
To realize a device that circumvents losses in coupling superconducting circuits to external quantum amplifiers by embedding an artificial atom within a flux-pumped Josephson parametric amplifier, enhancing dispersive measurement efficiency while minimizing excess backaction.
研究成果
The study demonstrates a QPA device achieving up to 80% measurement efficiency by mitigating off-chip losses through on-chip gain, with good agreement between theoretical models and experimental results. Future improvements could involve stroboscopic measurement to eliminate parasitic dephasing and enhance efficiency further, making it suitable for quantum feedback and control applications.
研究不足
The device exhibits nonideal behavior at high measurement strengths or gains, such as spurious peaks in histograms, possibly due to population of higher transmon levels. Dynamic range is limited by nonlinearities, and improvements may require reducing χ/κ or increasing SQUID numbers. Off-chip losses and noise additions downstream affect overall efficiency.
1：Experimental Design and Method Selection:
The experiment involves designing a qubit parametric amplifier (QPA) by integrating a transmon qubit with a Josephson parametric amplifier (JPA) for on-chip parametric gain. Theoretical models based on Hamiltonian dynamics and master equations are used to describe the system.
2：Sample Selection and Data Sources:
A transmon qubit is fabricated on intrinsic Si with Al/AlOx/Al junctions, and parameters such as qubit frequency, coupling strength, and decay rates are measured across multiple cooldowns.
3：List of Experimental Equipment and Materials:
Includes a dilution refrigerator, vector network analyzer, microwave generators, amplifiers (e.g., JPA, JTWPA), circulators, filters, and cryogenic components. Specific devices are fabricated using photolithography and plasma etching.
4：Experimental Procedures and Operational Workflow:
The setup involves applying microwave tones for readout and pumping, switching on flux pumps, performing Ramsey experiments to measure dephasing rates, and integrating weak-measurement records to determine signal-to-noise ratios.
5：Data Analysis Methods:
Data are analyzed using Gaussian fitting for histograms, theoretical models for dephasing rates, and efficiency calculations based on signal-to-noise ratio and dephasing rate ratios.
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