Millimetre-Wave Superconducting Quantum Amplifiers for Radio Astronomy

高灵敏度的弱信号放大几乎完全是使用高电子迁移率晶体管（HEMT）放大器实现的。它们是天文学、量子计算、地球观测和低温物理学最高灵敏度仪器的组成部分。然而，HEMT放大器具有基本的缺点。灵敏度仍然超出可以实现的范围，以接近量子极限水平。它们耗电量大，需要大量散热，并且噪声温度和带宽在较高频率下迅速恶化。因此，对于开发具有量子限制噪声性能、在宽带宽上的高增益、超低功率耗散并且能够在毫米（mm）和亚毫米波长范围中操作的新放大器技术存在强烈的兴趣。新兴的超导参量放大器（SPA）技术有可能实现所有这些要求。放大是通过经由强“泵浦”波改变器件电抗来实现的，该强“泵浦”波将允许功率从强泵浦传输到弱信号。由于该过程完全依赖于超导非线性反应响应，耗散非常小，因此可以达到量子极限。它们的尺寸也很小，坚固耐用，用途广泛，制造产量高。这一领域的大多数已发表的工作都描述了只能在微波频率下工作的SPA。该博士项目旨在开发一种宽带SPA，该SPA将在毫米波范围内工作，作为为无线电，毫米和亚毫米天文接收器开发的量子混频器的前置放大器。这种器件的发展将在毫米和亚毫米天文学和B模式宇宙微波背景（CMB）实验中产生巨大的影响，因为在混频器或第一级检测器之前具有高增益的量子噪声限制SPA将使接收机灵敏度提高一个数量级以上。在这个项目中，学生将学习理论背景和模拟技术来模拟SPA，沿着学习使用商业电磁学软件来设计放大器。学生将有机会使用最先进的洁净室设施参与设备的制造，无论是在牛津还是与我们的其他合作者。学生还将学习如何使用亚开尔文低温系统和其他实验技术，用于测量放大器的性能。特别是，学生将研究SPA在毫米波频率下的操作，以及它们对物理温度和用于形成SPA的超导材料的性能依赖性。最后，学生将整合放大器到现有的毫米波天文接收机，并评估对接收机性能的影响。这个项目属于天文仪器研究领域的福尔斯。

Amplification of weak signals with high sensitivity is almost exclusively achieved using high electron mobility transistor (HEMT) amplifiers. They are an integral part of the most highly-sensitive instruments for astronomy, quantum computing, Earth observation and low-temperature physics. HEMT amplifiers however have fundamental drawbacks. The sensitivity is still beyond what can be achieved, to approach the quantum limited level. They are power hungry, requiring substantial heat dissipation, and both the noise temperature and bandwidth deteriorate rapidly at higher frequencies. There is therefore an intense interest for developing a new amplifier technology with quantum-limited noise performance, high gain over wide bandwidths, ultra-low power dissipation and capable to operate in the millimetre (mm) and sub-mm wavelength regime. The emerging technology of superconducting parametric amplifiers (SPAs) has the potential to achieve all these requirements. Amplification is achieved by varying the device reactance via a strong 'pump' wave that would allow power transfer from the strong pump to the weak signal. Because the process relies purely on superconducting nonlinear reactive response, dissipation is exceedingly small, therefore allowing the quantum limit to be achieved. They are also small in size, robust and very versatile with high fabrication yield. Most published work in this area described SPAs that could operate only at microwave frequencies. This PhD project aims to develop a wideband SPA that would operate at millimetre wave regime as pre-amplifier for the quantum mixers developed for radio, mm and sub-mm astronomical receivers. The development of such a device will have a huge impact in mm & sub-mm astronomy & B-mode Cosmic Microwave Background (CMB) experiments, as a quantum-noise limited SPA with high gain before the mixer or the first stage detector will improve the receiver sensitivity by more than an order of magnitude. In this project, the student will be studying the theoretical background and simulation technique to model the SPA, along with learning to use commercial electromagnetism software to design the amplifiers. The student will have the chance to get involve in the fabrication of the devices using state-of-the-art clean room facilities, either here in Oxford, or with our other collaborators. The student will also learn how to use sub-Kelvin cryogenics system and other experimental techniques, for measuring the performance of the amplifiers. In particular, the student will investigate the operation of the SPA at mm-wave frequencies, and their performance dependence on the physical temperature and the superconducting materials used to form the SPAs. Finally, the student will integrate the amplifier into an existing mm-wave astronomical receiver and assess the impact on the receiver performance.This project falls within the astronomical instrumentation research area.