Revealing the high-redshift Universe with superconducting on-chip spectrometers

How did the Universe begin? When did the first galaxies form? What is "dark energy"? These are some of the major outstanding questions in modern astronomy and cosmology. The answers to these questions are encoded in the distribution of matter and how it has evolved throughout the history of the Universe. This fellowship will develop a novel sensor technology that will enable a new class of astrophysical experiments that will probe of the evolution of structure throughout cosmic time. When we point our telescopes toward the night sky, we observe light that originates from millions of stars and galaxies. Because light takes time to travel to us, we are effectively looking back in time, and by taking images of the night sky we are able to build up a picture of the history of distribution of matter as the Universe evolved. To extract all the information about a galaxy, a measure of the total brightness and the colour of the light is needed. Spectrographs are able to separate light into colours, and are a key tool that can be used to construct large catalogues of galaxies. These galaxy surveys, in combination with the cosmic microwave background (CMB), have shaped our current understanding of the origin, content, and evolution of the Universe. Despite this wealth of data, direct evidence of how our Universe began and a true understanding of dark energy remain elusive. Typical galaxy surveys are built using powerful telescopes that operate at optical/infrared wavelengths. This choice of wavelength is well suited to nearby galaxies, probing only late times whilst leaving the early Universe relatively undiscovered. The expansion of the Universe modifies the light emitted from very distant galaxies and stretches the wavelength into the sub-millimetre (sub-mm) wavelength range. Detection of this faint sub-mm light poses a number of challenges and requires a fundamentally different detection technology to traditional semiconductor arrays. While mature solutions exist for sub-mm single-colour cameras, technology for sub-mm spectroscopy is an area requiring dedicated development. Current state-of-the art instruments are bulky and expensive, often requiring moving parts that are challenging to scale. The main technical objective of this fellowship will be to develop a novel technology that provides a miniaturised, low-cost solution that takes advantage of well-established techniques. The key to this technology is a combination of finely tuned superconducting integrated circuits deposited on a single silicon wafer. With superconducting circuits defined lithographically, an entire spectrometer can be realised on a square centimetre of silicon; this functionality would previously have required an instrument close to a metre in size. The significant reduction in size and cost will enable the construction of 2D arrays with thousands of spectrometers, and building on the heritage and experience gained from initial proof-of-concept devices, this fellowship will develop, demonstrate, and optimise scalable on-chip superconducting spectrometers capable of operating over the entire sub-mm wavelength range. A dedicated demonstration at the Mexican 50-m Large Millimetre Telescope within this fellowship offers a unique opportunity to boost the maturity of this novel technology, and success would open up a new class of galaxy surveys that target the earliest galaxies in our Universe, complementing existing optical/infrared galaxy surveys. In fact, the combination of these techniques would serve as important systematic cross-checks, and cross-correlations between the surveys promise to be a powerful approach to further improve constraints on cosmological parameters.