Photometric and Spectroscopic Superconducting Imaging Technology for Astrophysics

The submillimetre-wave (3mm-300um) and far-infrared (300um-20um) regions of the electromagnetic spectrum are of considerable importance for astronomy because they contain a wealth of information about the cool, optically dark Universe. For example, the Cosmic Microwave Background radiation, which is a relic of the Big Bang, can be found at the longest wavelengths, and thermal radiation from distant, highly redshifted galaxies can be found at the shortest wavelengths. These regions also contain thousands of spectral lines from numerous molecular and atomic species, which are important for studying the chemistry and physics of regions where stars and planets are being formed. It is exceptionally difficult to carry out astronomy at submillimetre wavelengths because observations must be made from high dry sites in remote places or from space. The detection of signals requires large and expensive telescopes, and complex instruments must be cooled to temperatures of between 4K and 100 mK. It is simply not possible to buy suitable cameras and spectrometers, and instead astronomers must develop their own 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. Superconductors have the property that their electrical resistance falls to zero below a critical temperature, and magnetic flux is expelled. Indeed, the superconducting state is a distinct state of matter, which has many curious properties. By fabricating microcircuits from Nb, Ta, Al, Mo, NbN and NbTiN and by using modern Si and SiN micromachining techniques, it is possible to make detectors having extraordinary characteristics. For example, some of our infrared detectors are capable of sensing a 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 conversion gain and sensitivities limited by the Heisenberg uncertainty principle. The programme described in this application concentrates on three specific devices: (i) Transition Edge Sensors (TESs), 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 SiN island; (ii) Kinetic Inductance Detectors (KIDs), which essentially measure a small change that occurs in the amount by which magnetic field penetrates into the surface of a superconductor when photons are absorbed; (iii) Superconductor Insulator Superconductor (SIS) mixers, which use extremely thin layers of superconducting and insulating material to create diodes, in which quantum mechanical tunnelling occurs, creating highly sensitive radio receivers. Each of these device types can be used singly or packed into arrays of multiple pixels to form cameras. Superconducting mixers require coherent, phased locked reference sources called local oscillators, which are extremely difficult to realise at supra-THz frequencies. The development of suitable coherent source technology is therefore an essential part of our programme. Another innovative part of our proposed work is to develop microscopically patterned phononic filters that control the flow of heat onto devices, and reduce thermal fluctuation noise, by forming filters that attenuate elastic waves in support structures. The core themes of our proposed research into quantum sensor physics are intrinsically intellectually fruitful, and are of central importance to enabling major areas of astronomy. At the end of the work, we will have demonstrated a new generation of imaging technology based on advanced superconducting devices that will be available to construct the highly sensitive submillimetre-wave and far-infrared instruments needed for the next generation of ground-based and space-borne astronomy.

Our Consortium works on the development of advanced imaging technology for the next generation of submillimetre-wave and far-infrared ground-based and space-borne astronomical telescopes. Most modern
instruments are complex, and require a diverse range of international expertise in order to achieve the extraordinary levels of performance that are now needed. We see our role as exploring and understanding the physics of quantum sensors, innovating and developing photometric and spectroscopic imaging technology to TRL 4/5, and providing the community with ultra-low-noise components in the form of proven subsystems for major projects. In this way we can help lever opportunity for the UK in high-profile areas of fundamental science. Over the years, we have contributed significantly to the success of many projects (JCMT, ALMA, Herschel HIFI, etc.), and our Consortium is well connected to numerous overseas organisations (GSFC, SRON, ESA, ESO, PTB, VTT, IRAM, JPL, CalTech, CfA). Not only is our work of pivotal importance for astronomy, it is highly intellectually rich in its own right, and our groups have made numerous contributions to theoretical and far-infrared optics, device physics, materials science and device processing. Our work spans the astronomy/solid-state physics divide, exchanging knowledge in both directions. Since 2009 members of the Consortium have published 118 journal and conference papers, many of them in high quality journals such as Phys. Rev. A and B, Phys. Rev. Lett., Sup. Sci. Tech., Teraherz Sci. Tech., JOSA. In addition to fundamental science, our work has great commercial significance in areas such as sensors for Earth observation, weather monitoring, communications, surveillance, biological sensing, medical and plasma diagnostics. For example, the RAL MMT group works closely with industry: e.g. Astrium UK, JCR Systems, SEA Ltd, Oxsensis, Nav Tech, and national and international organisations such as HEIs, the Met Office, EU, SAO, and DLR. RAL has now formed a spin out company, Teratech Components Ltd, to exploit its Schottky-diode foundry. Likewise, the Oxford Group has developed a new feed-horn technology, which is being used widely and commercialized through MM Microwaves, with the appropriate the IP protection in place. The Cambridge Group has a licensing agreement with Oxford Instruments PLC, and formal Agreements with a number of large international organisations, such as PTB and SWRI. Although the emphasis in this proposal is on astrophysics, our work is strongly coupled to the STFC's Grand Challenge themes of the Environment and Security. The Univ. Cambridge has for instance just established a 1.5 year pilot study called SPECTRO-ICE (Prof Withington as PI) to bring together the Cavendish Laboratory, British Antarctic Survey and the Department of Mathematics to assess quantitatively how technology developed for submillimetre-wave astronomy can be used to address key problems in atmospheric science. Prof. Yassin has been particularly active working with academic institutions in the developing world to help establish research via technology transfer and training young scientist: specific examples include Univ. Al-Akhawayn in Morocco, Univ. UTAR in Malaysia, Univ. Mahidol in Bangkok, Univ. Beihang in China, and the Univ. Qatar in Doha. All of the Consortium partners engage fully with the Outreach offices of their respective institutes, and give talks to professional bodies, clubs, and schools. Our groups have looked after school and undergraduate vacation project students, and we will continue to inspire young people in this way. In Oxford Astrophysics, the citizen science projects GalaxyZoo, MoonZoo and Planet Hunters allow members of the public to participate in scientific research, and they already have more than 480,000 registered users. Our PhD students always move on to high-achieving scientific careers in areas such as the Home Office, Patent Office, industry and professional research.