Quantum-enhanced interferometry for new physics

Modern physics explains a stunning variety of phenomena from the smallest of scales to the largest and has already revolutionized the world! Lasers, semi-conductors, and transistors are at the core of our laptops, cellphones, and medical equipment.
And every year, new novel quantum technologies are being developed within the National Quantum Technology Programme in the UK and throughout the world that impact our everyday life and the fundamental physics research that leads to new discoveries. Quantum states of light have recently improved the sensitivity of gravitational-wave detectors, whose detections to date have enthralled the public, and superconducting transition-edge-sensors are now used in astronomy experiments that make high-resolution images of the universe. Despite the successes of modern physics, several profound and challenging problems remain. Our consortium will use recent advances in quantum technologies to address two of the most pressing questions: (i) what is the nature of dark matter and (ii) how can quantum mechanics be united with Einstein's theory of relativity?

The first research direction is motivated by numerous observations which suggest that a significant fraction of the matter in galaxies is not directly observed by optical telescopes. This mysterious matter interacts gravitationally but does not seem to emit any light. Understanding the nature of dark matter will shed light on the history of the universe and the formation of galaxies and will trigger new areas of research in fundamental and possibly applied physics. Despite its remarkable importance, the nature of dark matter is still a mystery. A number of state-of-the-art experiments world-wide are looking for dark matter candidates with no luck to date. The candidate we propose to search for are axions and axion-like-particles (ALPs). These particles are motivated by outstanding questions in particle physics and may account for a significant part, if not all, of dark matter. First, we propose an experiment which will rely on quantum states of light and will detect a dark matter signal or improve the existing limits on the axion-photon coupling by a few orders of magnitude for a large range of axion masses. Second, we will build a quantum sensor which will improve the sensitivity of the international 100-m long ALPS detector of axion-like-particles by a factor of 3 - 10.

Our second line of research is devoted to the nature of space and time. Recent announcements of Google's Sycamore quantum computer and the detection of gravitational waves have provided additional evidence to the long list of successful experimental tests of quantum mechanics and Einstein's theory of relativity. But how can gravity be united with quantum mechanics? To seek answers that inform this question, we propose to study two quantum aspects of space-time. First, we will experimentally investigate the holographic principle, which states that the information content of a volume can be encoded on its boundary. We will exploit quantum states of light and build two ultra-sensitive laser interferometers that will investigate possible correlations between different regions of space with unprecedented sensitivity. Second, we will search for signatures of semiclassical gravity models that approximately solve the quantum gravity problems. We will build two optical interferometers and search for the first time for signatures of semiclassical gravity in the motion of the cryogenic silicon mirrors.

Answering these challenging questions of fundamental physics with the aid of modern quantum technologies has the potential to open new horizons for physics research and to reach a new level of understanding of the world we live in. The proposed research directions share the common technological platform of quantum-enhanced interferometry and benefit from the diverse skills of the researchers involved in the programme.

The PI and CIs expect to deliver a range of positive impacts from day one of the programme. Foremost are scientific results of the research programme with immediate relevance to scientists in related fields worldwide. The results of the dark matter searches and of the search for quantization of space-time, very high-frequency gravitational waves, and semiclassical gravity, as well as the underpinning experimental techniques and theoretical investigations will be published in high profile scientific journals, such as Nature, Science and Physical Review Letters.
The PI and CIs, as well as the PDRAs and PhD students will also share their results at national and international conferences and workshops, with a strong presence of leading academic researchers and commercial companies. The outputs of the consortium will be more widely promoted through the use of social media, a website, and engagement with the public outreach team at Cardiff, Birmingham and Glasgow Universities to produce press releases. Data collected from the table-top experiment will be freely available after the collaboration ran it through their pipelines.
Starting from the beginning of the project, the PI and CIs will organise and participate in outreach events to promote dark matter searches among a wider audience. During the duration of the grant, we will build a small-scale prototype of an axion interferometer. We will bring this setup to the outreach events and demonstrate the key principles of the axion searches.

The researchers of the consortium will have regular meetings with researchers and industry partners from the UK National Quantum Technology Programme (the QT hub in Sensing and Timing and and QuantIC, the QT hub in Imaging), to discuss new ideas and the progress of the proposed experiments. Since the proposed research programme will use and further develop quantum techniques to improve the sensitivity of the optical interferometers, it has the potential to find applications in the quantum technology developed and commericalised through the hubs.

The consortium will lead an international collaboration network of researchers from the UK, Europe, the US that search for dark matter using interferometry. In the medium term, the network has the potential to build several table-top interferometers, cross-correlate their data, and develop new ideas for future detectors. The UK has already gained a solid reputation in dark matter searches. The consortiums international collaboration with further strengthen it.

Apart from academic impact, the proposed research will contribute to the development of seven PDRA and three PhD students. The PI and CIs will provide training to their teams in a range of physical and engineering fields, such as dark matter searches, precision measurements, electronics, feedback control theory and data analysis. Once the project is complete, the PDRAs and the PhD students will be able to apply these skills in both academic research and industry.