Miniaturized Atomic Gyroscopes
Goals and background
Future mobility solutions, like automated driving, require high-performance inertial sensors such as accelerometers and gyroscopes. Quantum gyroscopes have the potential to reach the unprecedented accuracy and stability required for this application. Atomic gyroscopes are highly sensitive quantum devices that use the nuclear spins in an atomic gas for rotation measurement. Miniature Atomic Gyroscopes (MAG) employ noble-gas nuclear spins as high-coherence rotation sensors. Advanced prototypes exist but the application remains confined to laboratory environments. The primary challenges for MAGs are the long relaxation times that give nuclear-spin devices exquisite long-term stabilities but also lead to narrow resonances that limit the gyroscope operational bandwidth.
First generations of atomic gyroscopes used handmade glass cells – limited in both miniaturization and cost reduction. In macQsimal, we deployed vapor cells fabricated using cost-efficient MEMS processes. New quantum gyroscopes utilise more drift stability than ever before, paving the way for fully internal navigation and improved safety in highly autonomous driving.
Key results and impact
- Fabrication, characterization and optimization of atomic MEMS and glass vapor cells containing alkali and noble-gas atoms
- Measurement of Larmor precession of noble-gas nuclear spins with coherence times of serval seconds
- Sealing of MEMS vapor cells in a low-temperature cofired ceramic (LTCC) package that allows for good thermal and mechanical isolation
- Set-up of a table-top experiment for vapor cell characterization and proof-of-principle tests via the application of an emulated rotation rate
- A novel approach in the assessment and benchmarking of the gyroscope bandwidth
- Design, and characterization of components of a compact gyroscope demonstrator suitable for rotation rate measurements
- Development of a system model of an atomic gyroscope
- Design and implementation of control, driving and readout electronics using a field-programmable gate array platform
- Theoretical study of nuclear spin squeezing in Helium-3 for reduction of quantum noise
Nuclear Magnetic Resonance Gyroscopes for Precise Positioning
Robert Bosch GmbH (BOSCH), 2020, 1st ZULF NMR Conference, online.
Simulations and Control Theory for Nuclear Magnetic Resonance Gyroscopes
Robert Bosch GmbH (BOSCH), 2020, micro-WOPM 2020, online.
The macQsimal partners produced seven deliverables on miniature atomic gyroscopes. Please refer to the list of publicly available deliverables for more details.
- Prediction of NMR Gyroscope Performance using Numerical Modelling BOSCH, 2021, WOPM, online
- Simulations and Control Theory for Nuclear Magnetic Resonance Gyroscope BOSCH, 2020, µ-WOPM, online
- Nuclear Magnetic Resonance Gyroscopes for Precise Positioning BOSCH, 2020, 1st ZULF NMR, online
Establishing a sensing principle
Atomic rotation sensor detects the angular rate of an object by measuring a shift in the precession frequency of nuclear spins of atomic gas. Typically, the atomic gas is a combination of alkali vapor, e.g. rubidium, and a noble gas, e.g. xenon, confined in a small vapor cell. The nuclear spins of the noble gas are used for rotation detection, whereas the alkali vapor is an auxiliary gas used for initialization and readout via pump and probe laser beams. The applied magnetic fields determine the gyroscope’s measurement axis and drive the atomic spin precession.
The right vapor cell
For the fabrication for the MAGs, we used a gas mixture of rubidium and xenon that was confined in a small vapor cell. We fabricated and investigated various cell designs, ranging from glass-blown vapor cells of different geometries with a volume of about 1 cm³, fabricated by the University of Neuchâtel, to MEMS vapor cells that consist of a glass-silicon-glass stack with a volume of 1-10 mm³ fabricated at CSEM.
The vapor cells were placed at the center of a magnetic shielding with an integrated triaxial coil system for magnetic field generation. A pump and a probe laser beam optically polarized and read out the spin precession, respectively. The electronic data processing and feedback control determined the rotation rate from the optical signal and controlled the applied fields.
Within the macQsimal project, the team at Bosch research built a large optical setup for proof-of-principle experiments and designed a compact demonstrator suitable for rotation rate measurements.
Towards market applicability
Precise position data of vehicles are essential for modern mobility solutions. In the case when GPS signals and other systems observing the environment are temporarily unavailable, high-performance inertial sensors will be the only remaining navigation system using dead reckoning i.e. localization based on a previously determined position and precise directional sensor signals from accelerometers and gyroscopes. Utilization of quantum effects in atomic vapor cells allows for high precision measurements of rotation rates and shows great promise for further miniaturization.