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.
