Quantum mechanics (QM) and general relativity (GR) are the most successful and profound theories of the 20th century. Beyond their insight into the workings of nature, they impact our lives from quantum technology in medicine or smartphones to GPS-guided navigation. It is not known though, how to combine General Relativity with quantum mechanics. In our laboratory at Cardiff University we aim to conduct one of the first empirical probes of the foundational conflict between quantum mechanics (QM) and general relativity (GR). [1] We have been commissioning an instrument since 2019 to probe the symmetries and foundational principles of quantum space-time using precision laser interferometers enhanced with state-of-the-art quantum technology. Over the next years, we will work on a new design that brings together for the first time technologies from opposite regimes - the high-power metrology of LIGO and GEO600 with superconducting nanowire single-photon detector (SNSPD) readout - to achieve a significant leap in sensitivity, surpassing the theoretically predicted levels necessary for a possible detection of quantized space-time. Our new design will use optical filter cavities to find a few "needles" - signal photons, which have different frequencies after being perturbed by quantum space-time fluctuations - in a "haystack" of carrier photons. You will work on the design, building, and "making to work" of optical filter cavities which reject the regular carrier photons, but let pass the rare signal photons which then get counted by the single-photon detectors. This is a project at the edge of technical possibility and an exciting opportunity to learn optical engineering techniques, digital controls, and noise analysis. You will work in a team-oriented environment but have your own project, which is embedded in a larger experimental setup. All the relevant techniques are highly applicable in industry, but are used here for the exciting search for new physics. Finding the graininess of space-time would give a powerful hint for a theory of quantum gravity and open up the field of experimental quantum gravity.