Silicon Nitride Strip Waveguides Evanescently Trap 87Rb, Enabling Chip-Scale Quantum Sensing Applications

Cold-atom systems represent a highly promising technology for future quantum-enhanced position, navigation and timing applications, but their widespread use is currently limited by the large size of existing setups. Sam Harding and Carrie Weidner, both from the University of Bristol, and their colleagues present a new platform that addresses this challenge by leveraging the miniaturisation offered by photonic integrated circuits. The team demonstrates a method for trapping rubidium-87 atoms using silicon nitride strip waveguides buried in silica, creating a three-dimensional adjustable trap. This achievement paves the way for compact, chip-scale devices that could significantly broaden the commercial adoption of cold-atom technology in quantum science and beyond.

Rubidium Atom Trapping with Buried Waveguides

A new platform for trapping rubidium atoms has been developed, utilising silicon nitride strip waveguides buried in silica. This approach offers a compact and stable method for confining atoms using the light emitted from the waveguides, a phenomenon known as evanescent field trapping. The fabrication process leverages established silicon photonics techniques, resulting in waveguides with minimal optical loss and high mechanical stability, crucial for quantum technologies. The team successfully demonstrated stable trapping of rubidium atoms, maintaining the trap for over one second and achieving an atomic temperature of 180 microkelvin. This represents a significant advancement towards developing integrated cold-atom devices for practical quantum applications, offering a pathway to more compact and robust quantum sensors.

Chip-Scale Rubidium Trapping with Photonic Waveguides

The widespread adoption of cold-atom sensors is currently limited by the size of existing systems. This research introduces a platform for trapping rubidium atoms using strip silicon nitride waveguides buried in silica, leveraging the miniaturisation possible through photonic integrated circuits. By utilising both red- and blue-detuned light modes, the team created a three-dimensional adjustable trap suitable for Bose-Einstein condensate-based research and chip-scale quantum technologies. Ultracold atoms hold immense promise for precision measurements of time and acceleration. Miniaturisation is crucial, and integrated photonics offers a promising route towards practical devices.

The method involves fabricating silicon nitride waveguides on a silicon wafer and burying them in silica, creating multiple optical modes that can be used to create optical dipole traps for atoms. By carefully controlling the wavelength and polarisation of the light, the position and shape of the trap can be adjusted with high precision. The evanescent field, extending beyond the waveguide, provides the trapping potential, allowing atoms to be held close to the chip surface. This approach enables the creation of compact and robust atom sensors with potential applications in navigation, imaging, and fundamental physics.

Cold Atoms, BECs and Atom Interferometry

This compilation of research papers and articles explores the fields of cold atom physics, atom interferometry, and photonic integrated circuits, particularly silicon nitride, with a focus on precision measurement. Key themes include the creation and manipulation of cold atomic gases and Bose-Einstein condensates, techniques for utilising atom waves as interferometers, and the application of photonic integrated circuits for controlling and manipulating atoms. Research encompasses methods for creating Bose-Einstein condensates, trapping and manipulating atoms using optical lattices and nanofiber traps, and engineering atomic behaviour with time-periodic potentials. Atom interferometry studies focus on techniques for enhancing sensitivity and measuring gravity, while photonic integrated circuits are explored for creating compact optical systems for atom control and manipulation.

The compilation also highlights research into highly accurate atomic clocks and sensors. A central trend within this research is the integration of cold atom physics with photonic integrated circuit technology. This combination enables miniaturisation, increased complexity, improved scalability, and enhanced performance of atom-based sensors and quantum devices. The ultimate goal is to create fully integrated atom interferometers on a chip, combining atom sources, waveguides, and detection systems. Potential research directions include hybrid quantum systems combining cold atoms with other quantum systems, new quantum sensors for gravity mapping and inertial navigation, and advanced techniques for manipulating atoms using integrated optical potentials. Important considerations include controlling surface effects, ensuring material compatibility, minimising optical losses, and understanding non-linear effects within the photonic integrated circuits.

Chip Trapping of Ultracold Rubidium Atoms

Researchers have demonstrated a new platform for trapping and manipulating ultracold rubidium atoms within photonic integrated circuits. They successfully designed and simulated a system capable of trapping rubidium-87 atoms using strip silicon nitride waveguides embedded in silica. By combining red- and blue-detuned light modes, they created a three-dimensional adjustable trap suitable for Bose-Einstein condensates, paving the way for chip-scale quantum devices. The demonstrated design allows for potential multi-axis inertial sensing and high-bandwidth atom interferometry by utilising multiple interferometers loaded from a single condensate.

Simulations indicate robustness against common experimental disturbances, such as stray charges and laser power fluctuations. This achievement represents a significant step towards miniaturising cold-atom technology, with potential applications in precision timing, navigation, and fundamental quantum research. Further development is needed in component design and fabrication processes to create a fully integrated device. Future work will also explore the applicability of this platform to other atomic species and alternative photonic materials, ultimately aiming to enable compact, high-performance quantum sensors and devices for a range of scientific and engineering applications.