AI 中文总结
本研究对比基于SQUID的约瑟夫森参量放大器（JPA）的保相与相敏工作模式，采用JPA-TWPA级联放大方案测得相敏模式下噪声温度远低于标准量子极限，为量子器件的高保真直接探测提供了新途径。
AI 中文摘要
相敏参量器件可实现正交选择性放大，有望达到亚量子极限噪声性能。本研究中，我们探究了基于SQUID（超导量子干涉器件）的Josephson Parametric Amplifier（JPA，约瑟夫森参量放大器）的运行特性，对比了其在保相和相敏工作模式下的性能。该器件采用VTT SWAPS技术制备，以三波混频构型驱动，并在毫开尔文温度下通过反射式测量装置进行表征。为直接探测低JPA增益下的噪声性能，我们采用了级联放大方案，其中Traveling-Wave Parametric Amplifier（TWPA，行波参量放大器）为JPA的输出提供低噪声前置放大。在保相运行模式下，JPA表现出近量子极限性能，在6 GHz频率下系统噪声温度为$351\boldsymbol{\u00b1}53$ mK。相比之下，相敏运行模式下的最小系统噪声温度为$94\boldsymbol{\u00b1}12$ mK，远低于288 mK的标准量子极限。我们的结果表明，JPA-TWPA放大器级联为无需背景噪声扣除即可直接、高保真探测量子器件开辟了道路。
英文摘要
Phase-sensitive parametric devices enable quadrature-selective amplification with the potential for sub-quantum-limited noise performance. In this work, we investigate the operation of a SQUID-based Josephson Parametric Amplifier (JPA), comparing its performance in the phase-preserving and phase-sensitive regimes. The device, fabricated using VTT SWAPS technology, is driven in a three-wave mixing configuration and characterized in a reflection-based measurement setup at millikelvin temperatures. To directly probe the noise performance at low JPA gains, we employ a cascaded amplification scheme in which a Traveling-Wave Parametric Amplifier (TWPA) provides low-noise pre-amplification of the JPA output. In a phase-preserving operation, the JPA exhibits near-quantum-limited performance with a system noise temperature of $351\pm53$ mK at 6 GHz. In contrast, phase-sensitive operation yields a minimum system noise temperature of $94\pm12$ mK, well below the standard quantum limit of 288 mK. Our results demonstrate that a JPA-TWPA amplifier cascade opens the door to direct, high-fidelity probing of quantum devices without the need for background noise subtraction.
Comments13 pages, 3 figures
DOI：10.1007/s10909-026-03458-9
