Quantum Technologies for Axion Dark Matter Search

Project Information

DarkQuantum

Grant agreement ID: 101118911

DOI

10.3030/101118911

EC signature date 30 September 2024

Start date 1 October 2024

End date 30 September 2030

Funded under

• European Research Council (ERC)

Total cost

€ 12 975 660,00

EU contribution

€ 12 975 660,00

Coordinated by

UNIVERSIDAD DE ZARAGOZA
Spain

Periodic Reporting for period 1 - DarkQuantum (Quantum Technologies for Axion Dark Matter Search)

Reporting period: 2024-10-01 to 2026-03-31

Summary of the context and overall objectives of the project

The nature of dark matter remains one of the most important open questions in modern physics. Among the leading candidates, the axion is particularly attractive because it could simultaneously explain dark matter and solve a long-standing problem in particle physics known as the strong CP problem. Despite decades of experimental effort, however, most of the theoretically favored axion parameter space remains unexplored, largely because existing detection technologies are approaching their fundamental sensitivity limits.

The most successful experimental strategy, the axion haloscope, searches for the conversion of dark matter axions into microwave photons inside a resonant cavity placed in a strong magnetic field. While this technique has achieved remarkable results, it faces two major challenges. At higher axion masses, the required cavities become smaller and produce weaker signals, while conventional microwave amplifiers are ultimately limited by quantum noise. These limitations prevent current experiments from reaching the sensitivity required to explore the most weakly interacting QCD axion models.

Recent advances in quantum technologies provide a unique opportunity to overcome these obstacles. Quantum sensors, including superconducting circuits, quantum-limited amplifiers and single-photon detectors, can dramatically reduce detector noise and enable sensitivities well beyond the standard quantum limit. These developments open the possibility of a new generation of axion experiments based on quantum-enhanced detection.

DarkQuantum aims to exploit these emerging technologies to achieve a major leap in the sensitivity of axion searches. Its central objective is to develop and demonstrate quantum-enhanced axion haloscopes capable of delivering competitive physics results during the project. The project follows two complementary approaches: a high-frequency experiment (DQHF), using quantum single-photon counters to search for higher-mass axions in the 8-18 GHz range, and a low-frequency experiment (DQLF), targeting ∼200–500 MHz with quantum-limited amplifiers in a large-scale haloscope integrated with the BabyIAXO magnet.

To achieve these goals, DarkQuantum addresses several key technological challenges, including the development of quantum sensors capable of operating in strong magnetic fields and at millikelvin temperatures, ultra-low-noise readout systems, and high-performance microwave cavities based on advanced superconducting materials. The project combines expertise in quantum technologies, cryogenics, particle physics and low-background experimental techniques, creating a unique interdisciplinary framework.

Scientifically, DarkQuantum has the potential either to discover axions or to completely rule out the standard axion dark matter paradigm in the stated frequecy regions. But the expected impact extends beyond the immediate search for axion dark matter. Technologically, it will demonstrate the power of quantum-enhanced detection for rare-event searches, establishing new methods that could benefit many areas of fundamental physics and precision measurement.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the reporting period, DarkQuantum has made major advances towards the realization of quantum-enhanced detectors for axion dark matter. Progress has been achieved across all major technological areas of the project, including quantum sensing, superconducting qubits, cryogenic systems, microwave cavities and system integration. Work has proceeded in parallel on the two experimental platforms, DQHF and DQLF, with close coordination between all consortium partners. Several milestones have already been reached, while new scientific opportunities have emerged beyond those foreseen in the original proposal. Most significantly, the DQLF prototype may be able to perform competitive dark matter measurements in the CERN M1 magnet as early as 2027.

A central objective of the project has been the development of quantum sensors capable of detecting the extremely weak microwave signals expected. For the DQHF experiment, the consortium has successfully demonstrated a quantum single-photon counter based on a superconducting qubit coupled to microwave resonators. A first proof-of-principle system, operated at Aalto, achieved very low dark count rates while already reaching sensitivity to unexplored dark photon parameter space. A second-generation detector, based on a cylindrical cavity better suited to the final experiment, has been built at CAPA and is currently under commissioning. Future work will optimize its performance and characterize its operation under increasingly realistic experimental conditions.

Since conventional superconducting qubits cannot operate in strong magnetic fields, DarkQuantum is also developing new qubit technologies compatible with the experimental environment of a RADES axion haloscope. First granular-aluminium (GraAl) transmons have been successfully fabricated at ENS and are currently being characterized. Additional developments, including GraAl fluxonium circuits and alternative superconducting materials, have also been initiated, extending the technological possibilities beyond the original project plan. Furthermore, a new "phase-resolved" detection concept has been proposed theoretically and is now being implemented experimentally at ENS.

For the DQLF experiment, important progress has also been achieved on a quantum-limited microwave amplifier based on SQUID technology. The amplifier has been successfully characterized under cryogenic conditions at KIT, confirming its suitability for the targeted low-frequency regime. It is being integrated with a dedicated high-speed digital readout system that will form the core of the detector electronics, being tested at DESY.

Substantial effort has also been devoted to the cryogenic and magnetic infrastructure required for both experimental platforms. For DQLF, two one-metre prototype resonant cavities have been designed at UPCT and are being constructed at KIT and CERN, together with the corresponding cryogenic system that will cool both the cavity and the quantum amplifier. In parallel, superconducting cavity coatings are being developed to further enhance detector performance. A proposal has been submitted to CERN to install this prototype in the M1 magnet, a unique 3 T superconducting facility. If approved, this would allow DarkQuantum to perform competitive physics measurements several years earlier than originally planned.

On the high-frequency side, an advanced RADES haloscope equipped with a quantum-limited travelling-wave parametric amplifier has been completed at MPP and is expected to begin physics operation shortly. This instrument will provide an important testbed for technologies that will later be integrated in the final quantum-enhanced DQHF setup, to be installed at CAPA. Preparations are also underway for a possible underground deployment, where the exceptionally low radiation environment may further reduce backgrounds.

Microwave cavity development has also progressed significantly. New high-T superconducting cavity designs have demonstrated quality factors between five and eight times higher than conventional copper cavities under strong magnetic fields, matching the best performances reported in the field. In addition, new frequency-tuning concepts based on ferromagnetic materials have been designed, simulated and experimentally tested. Preliminary results indicate that these systems can provide the large tuning ranges required to efficiently scan for axion dark matter while preserving excellent detector performance.

Overall, the first reporting period has successfully delivered the principal technological milestones envisaged for this stage of the project. At the same time, the advances achieved have opened new scientific opportunities, particularly the possibility of performing competitive dark matter searches well before the originally planned schedule, substantially increasing the expected impact of the DarkQuantum project.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The main achievements can be summarized as: (i) the development and early validation of both QLAD and QSPC sensors for the DQLF and DQHF systems, respectively; (ii) the identification of a major opportunity for early physics with the DQLF prototype at CERN, and concrete progress toward a realistic implementation of a DQLF setup at CERN as early as next year; and (iii) significant progress in enabling technologies, including HTS REBCO coatings for increased Q-factor and ferromagnetic tuning for frequency scanning. At the current stage, the project is on track to transition from technology development to fully integrated experimental demonstrators. By the end of the action, DarkQuantum is expected to deliver operational quantum-enhanced haloscope systems capable of performing competitive axion dark matter searches over a wide mass range, with sensitivity reaching or surpassing that required to probe the most challenging QCD axion models.