WP1
All partners contributed to the AQuRA clock system design, documented in deliverable D1.2.
WP2
VEXLUM provided the 461 nm high-power cooling laser based on its industrial VXL platform with intra-cavity frequency doubling. This single-oscillator design eliminates complex master-slave setups and provides high mechanical stability for TRL-ready deployment.
NKTP built two fiber-based laser systems:
• 689 nm cooling laser for micro-kelvin atom cooling.
• 698 nm ultra-stable clock laser for interrogation of the ¹S₀ → ³P₀ transition (~1 mHz linewidth).
Both rely on sum-frequency mixing of DFB fiber lasers and modular fiber-coupled components for long-term alignment-free stability. Housed in modified 3 HU 19″ racks with water cooling, they offer industrial robustness.
QuiX designed two integrated-photonics external-cavity lasers at 679 nm and 707 nm using silicon-nitride waveguides heterogeneously integrated with semiconductor amplifiers. Dual micro-ring resonators ensure single-frequency operation via the Vernier effect, with four heaters enabling wavelength and coupling control. The lasers couldn’t reach the required power levels and long-term stability and were therefore replaced by commercial OptoQuest ECDLs.
Exail built a 813 nm high-power magic-wavelength lattice laser based on fibre lasers and nonlinear conversion. Despite not reaching target power, it met optical specifications and was delivered as an integrated demonstrator.
WP3
UMK built a permanent magnet Zeeman slower and the electromagnetic coils that create the MOT quadrupole magnetic field and the offset fields. They also contributed the electronics that drives the electromagnets.
CNRS developed the Physics Package, containing the ultra-high-vacuum strontium source and integrated optics, sensors, and coils (MOT, bias, Zeeman slower). Tests at CNRS showed trapping and detection in the blue MOT and lattice; after shipment to Munich, vacuum remained at 5×10⁻¹⁰ mbar. Coils and drivers from UMK were installed and verified, with chiller and interlock systems operational and communication with control software confirmed.
UvA developed robotic manufacturing of optical circuit boards and produced the AQuRA optical circuit boards. These boards replace unstable optomechanical assemblies with glued, alignment-free optical circuits. Designs created in KiCad using newly created open-source optics libraries are transferred to a robotic pick-and-place system for fabrication. Six boards were produced for AQuRA.
WP4
CNRS developed the frequency converter module that translates the frequency comb repetition rate into useful rf signals. CNRS also contributed the high-level clock control software.
UvA developed the clock sequence control electronics and low-level software for the AQuRA clock, with custom sequencer, DDS, analog/digital I/O, and shutter driver boards. Firmware, drivers, and experiment-control software are open source (
https://github.com/opticsfoundry(öffnet in neuem Fenster)).
Menlo led integration and validation of the optical and frequency-reference infrastructure. Its subsystems—the Optical Reference System (1542 nm cavity, 10⁻¹⁵ instability at 1 s), 250 MHz SmartComb, Supercontinuum Module, Laser-Locking Electronics, and Spectral Purity Transfer (SPT) module—were integrated in two of four 19″ racks. The frequency comb bridges optical and microwave domains, while the SPT transfers sub-Hz linewidth stability from 1542 nm to 698 nm.
WP5
Menlo led integration of the AQuRA clock, with all relevant partners visiting to install their components.
Menlo, CNRS, UMK and UvA are currently bootstrapping the AQuRA clock, with a blue MOT achieved.
WP6
At PTB, nonlinear frequency drift of the Optical Reference System was analyzed with Menlo; mitigation strategies were identified to maintain clock accuracy. CNRS and PTB jointly prepared evaluation procedures using PTB’s software framework and defined data formats. Risks related to PTB laboratory renovation were mitigated through backup facilities.
WP7
UvA extended the White Rabbit time and frequency dissemination system to failsafe operation and prepared telecom network integration of the AQuRA clock.
WP8
UvA coordinated efforts in Dissemination and Public Engagement. UMK and UvA organised a Summer School, and MEN and UvA organized an international symposium. AQuRA was presented at the industry exhibition of ECAMP2025. Developments of a Quantum Teaching Kit is ongoing.
WP9
UvA managed the consortium.
