The integration of cold neutral atoms with nanophotonic circuits offers significant potential as a light–matter interface for a wide range of applications ranging from fundamental studies in quantum optics, quantum many– body physics, quantum networks to even ultracold chemistry. Here, we describe the design and realization of a novel platform where an efficiently–coupled microring photonic circuit on a chip is integrated with a cold atom system. This platform is fully compatible with laser cooling and trapping atoms, which allows for direct loading of cold atoms in close vicinity of a microring circuit. We discuss our experimental scheme and efforts to prepare for an array of individually trapped atoms within the near field region of a whispering-gallery mode (WGM) in a microring resonator for realizing strong atom–light interactions. Beyond our original motivations in creating an atom-photon quantum interface, we also discuss a novel application – for direct photoassociation (PA) synthesis and quantum state detection of cold diatomic molecules without closed optical transitions. We estimate that the transfer efficiency to a molecular ground state and the subsequent state detection efficiency can approach unity with strong photon–molecule coupling that could be realized in our microring resonator circuit.
The integration of cold neutral atoms with nanophotonic circuits offers significant potential as a light-matter interface for a wide range of applications ranging from fundamental studies in quantum optics, quantum many- body physics, quantum networks. Here, we demonstrate atom-photon interactions using an efficiently-coupled nanophotonic microring circuit on a chip. Cold atoms are prepared above the chip, and directed to the near field region of a whispering-gallery mode of a microring resonator by an optical dipole potential. Delivered atoms interact with the mode of a resonant light field coupled to the resonator. This demonstration of efficiently guided atoms and their interaction with a microring photonic circuit paves the way towards realizing an on-chip chiral atom-light interface.
Developing a hybrid platform that combines nanophotonic circuits and atomic physic may provide new chip-scale devices for quantum application or versatile tools for exploring photon-mediated long-range quantum systems. However, this challenging project demands the excellent integration of cold atom trapping and manipulation technology with cutting-edge nanophotonics circuit design and fabrication. In this thesis project, we aim to develop a novel suspended membrane platform that serves as a quantum interface between laser-cooled, trapped atoms in an ultrahigh vacuum and the photons guided in the nanophotonic circuits based on high-quality silicon nitride microring resonators fabricated on a transparent membrane substrate. The proposed platform meets the stringent performance requirements imposed by nanofabrication and optical physics in an ultra-high vacuum. These include a high yield rate for mm-scale suspended dielectric photonic devices, minimization of the surface roughness to achieve ultrahigh-optical quality, complete control of optical loss/in-coupling rate to achieve critical photon coupling to a microring resonator, and high-efficiency waveguide optical input/output coupler in an ultrahigh vacuum environment. This platform is compatible with laser-cooled and trapped cold atoms. The experimental demonstration of trapping and imaging single atoms on a photonic resonator circuit using optical tweezers has been demonstrated. Our circuit design can potentially reach a record-high cooperativity parameter C$>$500 for single atom-photon coupling, which is of high importance in realizing a coherent quantum nonlinear optical platform and holds great promise as an on-chip atom-cavity QED platform.
Interfacing cold atoms with integrated nanophotonic devices could offer new paradigms for engineering atom-light interactions and provide a potentially scalable route for quantum sensing, metrology, and quantum information processing. However, it remains a challenging task to efficiently trap a large ensemble of cold atoms on an integrated nanophotonic circuit. Here, we demonstrate direct loading of an ensemble of up to 70 atoms into an optical microtrap on a nanophotonic microring circuit. Efficient trap loading is achieved by employing degenerate Raman-sideband cooling in the microtrap, where a built-in spin-motion coupling arises directly from the vector light shift of the evanescent-field potential on a microring. Atoms are cooled into the trap via optical pumping with a single free space beam. We have achieved a trap lifetime approaching 700 ms under continuous cooling. We show that the trapped atoms display large cooperative coupling and superradiant decay into a whispering-gallery mode of the microring resonator, holding promise for explorations of new collective effects. Our technique can be extended to trapping a large ensemble of cold atoms on nanophotonic circuits for various quantum applications. Published by the American Physical Society 2024
We describe the design and fabrication of a scalable atom-light photonic interface based on a silicon nitride microring resonator on a transparent silicon dioxide-nitride multi-layer membrane. This new photonic platform is fully compatible with freespace cold atom laser cooling, stable trapping, and sorting at around
100 nm from the microring surface, permitting the formation of an organized, strongly interacting atom-photonic hybrid lattice. We demonstrate small radius ($R\sim
16μ$m) microring and racetrack resonators with a high quality factor
Q=3.2×105, projecting a single atom cooperativity parameter of
C=25 and a vacuum Rabi frequency of
2g=2π×340 MHz for trapped cesium atoms interacting with a microring resonator mode. We show that the quality factor is currently limited by the surface roughness of the multi-layer membrane, grown using low pressure chemical vapor deposition (LPCVD) processes. We discuss possible further improvements to a quality factor above
Q>5×106, potentially achieving single atom cooperativity parameter of
C>500 for strong single atom-photon coupling.
Trapped atoms near nanophotonics form an exciting platform for bottom-up synthesis of strongly interacting quantum matter. The ability to induce tunable long-range atom-atom interactions with photons presents an opportunity to explore many-body physics and quantum optics. Here we implement a configurable optical tweezer array over a planar photonic circuit tailored for cold atom integration and control for trapping and high-fidelity imaging of one or more atoms in an array directly on a photonic structure. Using an optical conveyor belt formed by a moving optical lattice within a tweezer potential, we show that single atoms can be transported from a reservoir into close proximity of a photonic interface, potentially allowing for the synthesis of a defect-free atom-nanophotonic hybrid lattice. Our experimental platform can be integrated with generic planar photonic waveguides and resonators, promising a pathway towards on-chip many-body quantum optics and applications in quantum technology.