The first tasks of macQsimal were dedicated to a review of state-of-the-art developments in the field of quantum sensors, as well as a deep survey on patents related to the five applications targeted in the project, including a check for the freedom to operate (FTO). The specifications for the different sensor prototypes and their essential building blocks were then defined and validated. The first technical tasks were dedicated to the atomic vapor cell designs and the corresponding quantum sensor prototype designs, considering the existing patents and the respective FTO.
The atomic vapor cell fabrication could start early in the project thanks to the validation of a new 6-inch wafer bonder at CSEM and to the development of a fully automated activation and characterization system. The first atomic vapor cells produced in macQsimal were for the miniature atomic clock, for which the design and the technological readiness level (TRL) was the most advanced at the beginning of the project. Vapor cells for the other applications were fabricated all along the project duration. Some redesign and additional fabrication runs were realized to correct for evidenced limitations or to allow for better performances and additional features.
The project objectives were reached thanks to an excellent teamwork, overcoming even the barriers imposed by the COVID-19 pandemic. A project extension of 10 months was nevertheless requested to allow finalizing the tremendous work foreseen in macQsimal, the result of which is summarized below in the form of a list of achievements:
The following prototypes and demonstrators were developed:
- Compact, high temperature, high-density optically-pumped magnetometer (OPM) prototype (based on MEMS atomic vapor cells) working in the spin exchange relaxation-free (SERF) regime. TRL 3 -> 4.
- Compact room-temperature low-density OPM prototype (based on specifically coated millimetre-sized glass atomic vapor cells). TRL 4 -> 6.
- Miniature atomic clock (MAC) pre-industrial prototype, including the physics package (PP), the electronic circuit board (EP) and the magnetic shielding. A low power electronic circuit articulated around an application specific integrated circuit (ASIC) was benchmarked with the EP. TRL 4 -> 6.
- Tabletop clock demonstrator based on a microfabricated Rb vapour cell and a miniature microwave resonator for pulsed interrogation based on Ramsey scheme. TRL 3 -> 4.
- Compact NMR-gyroscope (NMRG) demonstrator composed of the representative building blocks: MEMS atomic vapor cell, pump/probe laser sources, optics, magnetic shielding and coils. TRL 3 -> 4.
- Laboratory setup for imaging of microwave (GHz) fields using MEMS vapor cells, with frequency-tunability in the few GHz to tens of GHz range and sub-millimetre spatial resolution. The setup was also operated as a microwave analyser. TRL 2 -> 4.
- Laboratory experimental setup operated as a GHz field sensor for direct detection of microwave magnetic fields at GHz frequency.
- Laboratory setup for imaging of THz beams with frequencies in the THz gap range using standard optical cuvettes and MEMS cells, by detecting the E-field component with Rydberg atoms. The setup dimension could be reduced by 65%, proving that a low SWaP demonstrator is viable.
- Laboratory experiments in through flow cells with integrated electronics for Rydberg-based gas sensing of Rubidium and nitric oxide (NO), and their calibration at ppm/sqrt(Hz) levels.
The following quantum-enhancement strategies were conducted:
- Development of cavity-QED, spin squeezing, and optical squeezing methods for vapor-phase atomic sensors.
- Exploiting entanglement and spin squeezing in magnetometry: an improvement of ~10 % compared to the projection noise level.
- Theoretical study for quantum-enhancement strategies for NMR gyroscopes.
- Theoretical study for quantum-enhancement strategies for GHz field sensing with vapor cells.
In conclusion, the macQsimal consortium has reached most of its challenging objectives, both in terms of TRL increase and reduced time-to-market, and quantum-enhancement strategies for future high-performing novel quantum sensors.
