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Optical and Quantum Sensing and Precision Metrology II

Collective emission dynamics of many atoms coupled to a nanophotonic resonator

Ahreum Lee, Xinchao Zhou, Dipanjan Das, Shreya Jeedigunta, Saivirinchi Prabandhakavi, Chen-Lung Hung

Published Mar 5, 2026• 0 citations
Publisher

Abstract

Neutral atoms collectively coupled to a nanophotonic chip are key building blocks for quantum computers and quantum networks. We present our platform of cesium atoms integrated with a microring resonator, where approximately 70 atoms are trapped about 350 nm above from the microring surface using optical guiding and degenerate Raman sideband cooling. This setup enables the exploration of collective dynamics mediated by guided and radiative modes, leading to the observation of selective collective emission into the microring. We further discuss our progress toward implementing an evanescent trap geometry, which allows atoms to be brought closer to the microring surface and introduces spatial ordering. Trapping and cooling atoms in close proximity to nanophotonic structures advance the study of collective quantum optics and pave the way toward scalable quantum computers.

DOI
10.1117/12.3089897

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Neutral atoms collectively coupled to a nanophotonic chip are key building blocks for quantum computers and quantum networks. We present our platform of cesium atoms integrated with a microring resonator, where approximately 70 atoms are trapped about 350 nm above from the microring surface using optical guiding and degenerate Raman sideband cooling. This setup enables the exploration of collective dynamics mediated by guided and radiative modes, leading to the observation of selective collective emission into the microring. We further discuss our progress toward implementing an evanescent trap geometry, which allows atoms to be brought closer to the microring surface and introduces spatial ordering. Trapping and cooling atoms in close proximity to nanophotonic structures advance the study of collective quantum optics and pave the way toward scalable quantum computers.
We experimentally and theoretically study collective emission of a dense atomic ensemble coupled to a single mode in a nanophotonic microring resonator. Because many cold atoms are localized in a small volume, these trapped atoms collectively couple not only to the guided resonator mode but also to the nonguided modes in free space. Through tuning the atom-photon coupling and by adjusting the number of trapped atoms, we demonstrate superradiant emission to the microring resonator. For photon emission via the nonguided modes, our study reveals signatures of subradiance and superradiance when the system is driven to the steady state and to the timed-Dicke state, respectively. Our experimental platform thus presents the first atom-light interface with selective collective emission behavior into a guided mode and the environment. Our observation and methodology could shed light on future explorations of collective emission with densely packed quantum emitters coupled to nanophotonic light-matter interfaces.
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 discuss our recent experiment demonstrating superradiantly-coupled trapped atomic ensemble in an optical microtrap above a nanophotonic microring resonator. Here, efficient trap loading is achieved via a degenerate Raman-sideband cooling (dRSC) scheme using built-in spin-motion coupling in the microtrap and a single optical pumping beam sent from freespace. We show that these dRSC-cooled atoms display large cooperative coupling and enhanced superradiant decay into a whispering-gallery mode in the microring resonator.
Integrating the scalability of individually addressable arrays of optical-tweezer-trapped single atoms with the efficient light-matter interface provided by nanophotonic waveguides has been a long-standing challenge in quantum technologies based on atoms and photons. Here we realize a quantum interface between photons guided in an optical nanofiber with a diameter of 310 nm and an array of on average 155 individually addressable atoms. Using a spatial light modulator and an objective lens with NA = 0.45, single cesium atoms are trapped in a one-dimensional array of 200 optical tweezer spots with micrometer-scale trap sizes on the nanofiber. Individual atoms are addressed by spatially scanning an excitation laser beam, focused to a spot size comparable to that of the traps through the same objective lens, along the nanofiber. We confirm the single-atom nature of the individual trapping sites through photon-correlation measurements of the guided fluorescence, observing strong photon antibunching with g(2)(0)≈0.26g^{(2)}(0) \approx 0.26g(2)(0)≈0.26. We measure trap lifetimes of a few hundred milliseconds, with a maximum value of 460 ms, at an atom-surface separation of 670 nm without active cooling, representing an order-of-magnitude improvement over previous nanofiber traps. This platform opens a new regime for atom-photon interfaces, paving the way for scalable distributed quantum computing and quantum networks, as well as for the exploration of collective radiative effects in waveguide QED with individually addressable atoms.
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.
Strong atom-photon interactions on scalable photonic platforms hold significant potential for both atomic and photonic quantum information platforms. In particular, trapping of a single atom on a planar photonic integrated resonator at the subwavelength distances required for strong coupling to the guided modes has remained an outstanding challenge. Here we demonstrate efficient trapping of a single ultracold rubidium atom within the evanescent field of an integrated silicon-nitride microring resonator, at distances of 150-200 nm from the chip surface. Efficient, single-stroke loading process is achieved using an evanescent-field mechanism related to Sisyphus cooling, in which a single scattering event dissipates the atom's kinetic energy and transfers it into a near-surface trap. We observe logarithmic scaling of trapping durations spanning from sub-millisecond timescales up to 1 second, without continuous cooling. The trapped atom couples efficiently to the resonator, enabling on-chip photon collection, photon antibunching, and Purcell-enhanced spontaneous emission with single-atom cooperativity exceeding unity. Our results establish the potential of CMOS-compatible chip-based atom-photon interfaces for scalable quantum photonic circuits.