Quantum analysis of second-order effects in superconducting travelling-wave parametric amplifiers
Quantum analysis of second-order effects in superconducting travelling-wave parametric amplifiers
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DOI：
10.1088/1361-6463/ac0b74
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发表时间：
2021-04
期刊：
影响因子：
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通讯作者：
Songyuan Zhao;S. Withington
中科院分区：
文献类型：
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作者：
Songyuan Zhao;S. Withington
我们对行波参量放大器(TWPA)进行了量子力学分析，以研究与其工作相关的五个实验现象，即阻抗失配效应、上空闲模的存在、量子噪声和热噪声的存在、压缩态的产生以及在放大过程中预压缩态的保持。我们的分析使用动量算符来描述量子化模式沿TWPA的空间演化。我们计算了由于行波放大器与其外部系统之间的阻抗失配而对泵浦幅度和放大器增益施加的限制。我们将我们的分析应用于上空闲模式，并证明它们将导致抑制增益。我们证明了理想的TWPA确实是量子受限的，即它引入了零点涨落的半量子，这是保相线性放大器可能产生的最小噪声贡献。通过考虑沿放大器传输线的分布源的影响，分析了与TWPA相关的热噪声。我们的分析预测，由于信号模和闲置模之间的混波，高增益极限下的热噪声将翻一番。我们研究了在直流偏置电流存在的情况下TWPA的工作，并证明了原则上可以产生高度压缩的态。然而，使用非简并的TWPA放大预压缩态通常会降低压缩优势。
We have performed a quantum mechanical analysis of travelling-wave parametric amplifiers (TWPAs) in order to investigate five experimental phenomena related to their operations, namely the effect of impedance mismatch, the presence of upper idler modes, the presence of quantum and thermal noise, the generation of squeezed states, and the preservation of pre-squeezed states during amplification. Our analysis uses momentum operators to describe the spatial evolution of quantised modes along a TWPA. We calculate the restriction placed on pump amplitude as well as amplifier gain as a result of impedance mismatch between a TWPA and its external system. We apply our analysis to upper idler modes and demonstrate that they will result in suppressed gain. We show that an ideal TWPA is indeed quantum-limited—i.e. it introduces a half-quantum of zero-point fluctuation which is the minimum possible noise contribution for a phase-preserving linear amplifier. We analyse the thermal noise associated with a TWPA by considering the effect of distributed sources along an amplifier transmission line. Our analysis predicts a doubling of thermal noise in the high gain limit as a result of wave-mixing between signal and idler modes. We study the operation of a TWPA in the presence of a DC bias current, and have shown that highly squeezed states can in principle be generated. However, amplifying a pre-squeezed state using a non-degenerate TWPA generally reduces the squeezing advantage.