Ultra-low-noise Superconducting Spectrometer Technology for Astrophysics

电磁波谱的微波（3厘米-3毫米）、亚毫米波（3毫米-300微米）和远红外（300微米-20微米）区域包含了关于寒冷黑暗宇宙的丰富信息。例如，宇宙大爆炸产生的微波辐射可以以最长的波长被发现，而来自遥远星系的热辐射可以以最短的波长被发现。这部分光谱还包含来自无数分子和原子物种的数千条光谱线，这对于研究恒星和行星形成区域的物理和化学非常重要。在亚毫米波段进行天文观测异常困难，因为地球大气中的水蒸气会吸收我们感兴趣的信号，而且观测必须在高度干燥的地方或从太空进行。探测亚毫米信号需要大型、精密的望远镜，复杂的仪器必须冷却到4 K到50 mK之间的温度。由于所需仪器的复杂性，不可能买到合适的相机等，因此天文学家必须开发自己的超灵敏成像技术。该计划旨在通过用超导体材料制造微电路来开发新一代极其敏感的探测器和接收器。超导态是物质的一种独特的状态，具有许多显著的特性。通过用某些金属和合金（Al, Mo, Nb, Ta, Ti, TiN, NbN）制造微电路，并使用现代硅微加工技术，可以制造出具有非凡特性的复杂电子器件。例如，我们的一些超导红外探测器可以在1000万英里的距离上探测到家用灯泡的开关时间仅为1秒，而其他探测器则以真正的量子力学方式运行，显示出非经典行为，灵敏度仅受海森堡测不准原理的限制。计划中的工作集中在三个特定的设备上：(i)过渡边缘传感器，它通过超导体到其正常状态的急剧转变来测量红外功率被微小的独立微型机械薄膜吸收时发生的微小温度变化；（ii）动能电感探测器，测量天文信号被吸收时磁场穿透超导体表面的微小变化；超导体绝缘体超导体混合器，它使用极薄的超导和绝缘材料层来制造二极管，在二极管中发生量子力学隧穿，从而作为高灵敏度的无线电接收器运行。这些设备中的每一个都可以单独使用，也可以打包成多个像素的阵列来形成相机。例如，我们的一个项目旨在开发毫米波光谱仪，用于研究CO等分子的高红移谱线，其中光谱仪的所有关键部件都制作在单个Si芯片上，并且仅使用数字电子器件读出。另一个项目旨在创建一个波长为0.46毫米的无线电接收器阵列，同样都在一个硅芯片上。这些超导混频器需要称为本地振荡器的参考源，这在太赫兹频率下很难实现。因此，本地振荡器技术的发展是我们计划的重要组成部分。我们提出的研究的核心主题本质上是富有智力成果的，并且对天文学的主要领域至关重要。在工作结束时，我们将展示基于先进超导设备的各种新成像技术，然后该技术将可用于为地基和天基天文望远镜构建新一代超灵敏仪器。

The microwave (3 cm-3 mm), submillimetre-wave (3 mm-300 um) and far-infrared (300 um-20 um) regions of the electromagnetic spectrum contain a wealth of information about the cold dark Universe. For example, microwave radiation originating from the Big Bang can be found at the longest wavelengths, and thermal radiation coming from distant galaxies can be found at the shortest wavelengths. This part of the spectrum also contains thousands of spectral lines from numerous molecular and atomic species, which are important for studying the physics and chemistry of regions where stars and planets are being formed. It is exceptionally difficult to carry out astronomy at submillimetre wavelengths because water vapour in the Earth's atmosphere absorbs the signals that we are interested in, and observations must be made from high dry sites, or from space. The detection of submillimetre signals requires large, precision telescopes, and complex instruments must be cooled to temperatures of between 4 K and 50 mK. Because of the complexity of the instruments needed, it is not possible to buy suitable cameras, etc., and so astronomers must develop their own ultra-sensitive imaging technology. The proposed programme aims to develop a new generation of extremely sensitive detectors and receivers by fabricating microcircuits out of materials called superconductors. The superconducting state is a distinct state of matter, which has many remarkable properties. By fabricating microcircuits from certain metals and alloys (Al, Mo, Nb, Ta, Ti, TiN, NbN), and by using modern silicon micromachining techniques, it is possible to make complex electronic devices having extraordinary characteristics. For example, some of our superconducting infrared detectors could detect a domestic light bulb being turned on and off for just 1 second at a distance of 10 million miles, whilst others operate in a truly quantum mechanical way, displaying non-classical behavior, and sensitivities limited only by the Heisenberg uncertainty principle. The planned work concentrates on three specific devices: (i) Transition Edge Sensors, which operate by using the sharp transition of a superconductor to its normal state to measure the minute change in temperature that occurs when infrared power is absorbed by a tiny free-standing micro-machined membrane; (ii) Kinetic Inductance Detectors, which measure the small change in the penetration of a magnetic field into the surface of a superconductor when astronomical signals are absorbed; and (iii) Superconductor Insulator Superconductor mixers, which use extremely thin layers of superconducting and insulating material to create diodes in which quantum mechanical tunnelling occurs, and thereby operate as highly sensitive radio receivers. Each of these devices can be used singly or packed into arrays of multiple pixels to form cameras. For example, one of our projects aims to develop a millimetre-wave spectrometer, to study the highly-redshifted spectral lines of molecules such as CO, where all key parts of the spectrometer are fabricated on a single Si chip, and read out using only digital electronics. Another project aims to create an array of radio receivers for a wavelength of 0.46 mm, again all on a single silicon chip. These superconducting mixers require reference sources called local oscillators, which are extremely difficult to realise at THz frequencies. The development of local oscillator technology is therefore an essential part of our programme. The core themes of our proposed research are intrinsically intellectually fruitful, and are of central importance in enabling major areas of astronomy. At the end of the work, we will have demonstrated various new imaging technologies based on advanced superconducting devices, and the technology will then be available to construct a new generation of ultra-sensitive instruments for ground-based and space-based astronomical telescopes.