Ultra-low-noise Superconducting Spectrometer Technology for Astrophysics

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.

As described in detail in our Impact Plan, our work benefits many communities, including astronomy, fundamental particle physics, atmospheric science, and quantum computing and communications. Our work also responds to a growing commercial interest in far-infrared laboratory-based spectroscopy for industrial process control, pollution monitoring, and security surveillance. Our underpinning research is wide ranging, both at the level of detailed technological techniques, such as microcircuit fabrication, through to the delivery of ultra-low-noise subsystems. As evidenced by Withington's success in raising infrastructure funding (£700k) for a new complex superconducting deposition system through an EPSRC Quantum Technologies Call, a highly active programme with UCL on developing spin-based quantum memory, and Tan's award of a Euro 2.0M European Research Council (ERC) Starter Grant for work on Superconducting Parametric Amplifiers, there are close synergies with the growing fields of quantum computing and communications, with much of the device physics and many of the technical problems being in common. All of the applications identified to date have excellent growth potential and, through industrial exploitation, represent opportunities for delivering intellectual status and financial return to the UK. For example, Cambridge has recently signed an agreement with NPL to develop its TES technology for low-energy electron spectroscopy in surface science, particularly XPS. The members of our Consortium access the considerable Outreach resources of their own institutes. Staff and students are encouraged to promote their work to a wide range of audiences including schools, colleges, visiting dignitaries and members of the public. The Physics Department at Cambridge has a substantial Outreach programme staffed by full-time professionals https://www.phy.cam.ac.uk/ covering school children, school leavers, and the general public. Withington and his team engage with this programme in a variety of ways, including giving tours to visiting parties. The Astrophysics Group at Oxford coordinates an extensive outreach programme organized by postgraduate students and postdocs in several areas of astronomy. This includes monthly telescope evenings, public and school talks and the Galaxy Zoo programme. RAL has extensive Outreach facilities directed towards increasing the public understanding of science. Public meetings are organised either on campus or at external locations, and numerous school and college visits are hosted yearly. For example, RAL opened its facilities for viewing by the public over one weekend in 2015. This event attracted over 16,000 visitors, who experienced a wide range of science and technology, presented by members of staff. RAL has a science and technology Exhibition Centre, which describes many of the activities undertaken by the Laboratory, and STFC as a whole. RAL-Space organises public events and visits to Departments, including the RAL-Space visitor centre. The RAL Millimetre-wave Technology Group, led by Ellison, regularly supports undergraduate and graduate industrial students in fulfilment of first or higher degree courses (e.g. from the Universities of Bath, Bristol, Cardiff and York) and hosts visiting scientists and students from overseas (e.g. from China, Japan, Korea, France and Spain). STFC and RAL have an extensive and coordinated website within which the RAL-Space Department and MMT Group are embedded (www.ralspace.stfc.ac.uk/Pages/Millimetre-Wave.aspx). Social media is used by RAL's public engagement professionals to promote events, achievements and opportunities. Regular press briefings are presented on the STFC website at www.stfc.ac.uk, and staff are encouraged to attend media awareness courses aimed at public communication. Overall, despite being a small team, we believe that we have a large impact across many areas of science, technology and education.