Quantum Sensing for the Hidden Sector (QSHS)

Identifying the nature of the dark matter that dominates the mass distribution of galaxies and that plays a key role in our understanding of cosmology is a central unsolved problem of modern physics. Attention over the past 30+ years has focused on weakly interacting dark matter (WIMPs); however, a smaller but active community has been searching instead for 'hidden-sector' particles, including the 'QCD axion', using some of the world's most sensitive electronics. Axions were invoked to solve the so-called strong-CP problem, whereby the theory governing strong interactions is far more symmetric than our current theory, quantum chromodynamics, say it should be. But axions also turn out to be a natural candidate for the mysterious dark matter.
Theory suggests that axions should be detectable through the tiny signals they emit, about a millionth of an attowatt, while traversing a microwave cavity in a strong magnetic field. These signals are at the limit of what can be detected using even cryogenically-cooled ultra-low-noise electronics, but in the past few years, rapid progress in developing newer and more sensitive quantum sensors, fueled by parallel research in quantum computing and measurement, has placed the detection of axions within our reach. The UK has considerable expertise in these new quantum devices, and this proposal aims to apply these pivotal new measurement technologies to the search for hidden sector particles.
Our proposed search has two main parts. First, we have reached out to the world's most sensitive axion search experiment, ADMX, proposing to form a UK-USA collaboration. ADMX has welcomed this approach, and is keenly encouraging our participation. The UK will design and install a new axion detector inside the magnet and cryostat that ADMX already operate. Using this detector, we will search for axions in our Galaxy's dark matter halo in a previously unexplored mass range between 25 and 40 micro-electron volts. This range is well matched to indications from current theories of what the axion mass might be, although the possible range of masses is far larger, and so there is a great deal of ground to cover. The UK instrument will have at its heart one of our own superconducting quantum measurement technologies - a bolometric detector, a coherent parametric amplifier, a SQUID based amplifier, or a qubit based photon counting device. The technology to be used will be selected after extensive characterisation at participating institutes. The chosen technology will then be integrated into the ADMX instrument module, which will be characterised in a dedicated 10 mK cryostat at the University of Sheffield. This same cryostat will then double as the first target in the UK high-field low-temperature test facility that forms the second part of our proposal.
Second, an internationally competitive UK effort in hidden sector physics needs a world class UK facility incorporating an extremely high field magnet: several times larger than those used for MRI imaging in health care. Such a magnet is necessary for axion searches, and axions are arguably the best motivated hidden sector dark matter candidate. The bore of the magnet needs to be very cold for the quantum electronics to work, about 10mK. We will partner with a national laboratory to build and operate a UK facility meeting these specifications. Many hidden sector search experiments could be housed in this facility, but the first one will be our own low-temperature quantum-spectrometer.
Finally, to help maintain the UK's international prominence in fundamental physics, we must create a research community. Hidden sector physics is a rapidly growing subject, and the discovery of a whole new class of particles would drive particle physics into a new era, and quantum electronics into new applications and markets. We believe that the technology and techniques developed will have applications in areas as diverse as quantum computing, communications and radar.

1. Impact on Knowledge: Results to be disseminated through open access publications in high impact journals spanning topics from quantum engineering through fundamental particle physics. We will endeavour to focus on journals such as Nature having wide distribution to academia, industry and the educated public. Major discoveries to be handled through University Press Offices after peer-review of science. Articles in profession-facing magazines such as IEEE Spectrum, Physics world. We will present at major national and international meetings such as the PATRAS workshop, IDM conference series, DESY workshops, APS meetings, and TAUP meetings. We will present the project UK National Quantum Technology Programme events organised by Hub partners nationally; these events are attended by diverse sectors beyond academia such as finance, security and defence. We will run an annual 2-day workshop where we will seek engagement from a wide community. Free exchange of staff and knowledge between the QSHS collaboration and our partners in ADMX will result in efficient bi-directional knowledge transfer between us and our US collaborators, and further opportunities for dissemination of knowledge to a wide audience beyond academia.
2. Impact on economy and society: The STFC/EPSRC delivery plan is designed to assist in the generation of an agile, creative, competitive UK economy. Our proposal is cross-disciplinary, combining knowledge across traditionally separated disciplines within physics and engineering. Our research will result in the training of many Ph.D. and postdoctoral staff with a wide ranging expertise that is in high demand. In bringing microwave quantum amplifiers, detectors, and photon counters with world-beating sensitivity and bandwidth to TRL5, we align with the STFC/EPSRC roadmap for quantum technologies, and develop new devices and techniques for growing commercial markets in quantum computation, measurement, cryptography and security. Our programme incorporates members of the UK National Quantum Technologies Programme, via consortium members from the National Physical Laboratory and the Oxford National Quantum Computing and Simulation Hub. NPL will facilitate economic and societal impact via the nearly complete Advanced Quantum Metrology Laboratory, bridging the gap to the relevant industry sectors. Our work has strong synergies with the Birmingham National Quantum Hub in Sensing and Timing (see attached letter of support). QSHS members have worked extensively in development of ultra-low-noise technology for diverse sectors such as space (Cambridge with ESA, UKSA, SRON, JPL, and Airbus) and healthcare (NPL with NHS England). Several QSHS members have been awarded patents in quantum measurement technologies. In summary, QSHS will work to project its research outputs beyond the academic community into industry and society, for the benefit of the UK economy.
3. Outreach impact
Fundamental science, and in particular the mystery of dark matter, are longstanding sources of public fascination. Quantum computing and quantum science in general are also subjects of intense public interest. See recent articles on axions in Forbes (19/11/19), and on quantum technologies in GQ Magazine (2/8/19). We will freely disseminate to the public the aims and fruits of our research, exploiting opportunities at IOP science festivals, open days, astronomy society meetings, and other public outreach events. We will engage with outreach activities of the DMUK UK dark matter community and the Quantum Hubs to reach the general public. We will in addition run our own collaboration web site.
4. Impact management
Coordination of these activities will be managed by staff to be selected from the collaboration during the opening phase of the project. The project steering committee will be asked to review and advise on impact activities as the project progresses.