Ultracold Atomic Lattice Deterministically Couples to Photonic Waveguide for Scalable Quantum Technologies

Controlling the interaction between light and matter at the nanoscale is a fundamental goal in modern optics and integrated technologies, yet combining the precision of cold atom research with the compactness of nanophotonic devices has proven remarkably difficult. Now, J. T. Hansen, F. Gargiulo, J. B. Mathiassen, and colleagues at the Niels Bohr Institute, University of Copenhagen, demonstrate a breakthrough in this field, achieving deterministic coupling between an ultracold atomic lattice and light confined within a suspended photonic waveguide. This achievement overcomes significant scalability challenges for neutral-atom quantum computers and simulators, promising faster optical readout and highly efficient light-matter interactions at the nanoscale. Beyond quantum technologies, the platform also enables novel imaging techniques, offering the potential for non-invasive, single-atom probes and three-dimensional microscopy of nanoscale structures.

These capabilities address scalability challenges in neutral-atom quantum computers and simulators, enabling fast optical readout, efficient and subwavelength non-diffracting interaction zones, and genuine compatibility with integrated solid-state photon sources, detectors, and stop-band modulators. Beyond controllable quantum matter, the platform also enables in-situ imaging of evanescent fields of light.

Atoms Coupled to On-Chip Photonic Circuits

Scientists engineered a platform for deterministically coupling ultracold atomic lattices to light propagating within suspended on-chip photonic circuits, achieving a breakthrough in hybrid integrated technologies. The study pioneered a method for trapping and delivering single atoms and atom arrays over millimeter-scale distances, retaining high fidelity and establishing a crucial link between free-space atomic arrangements and integrated nanophotonic structures. This involved fabricating waveguides from high-stress silicon nitride, leveraging mature nanofabrication techniques to integrate complex photonic structures with atomic systems and minimize transmission loss below 3 dB. The study demonstrated the ability to distinguish differences in the evanescent field with spatial resolution on the order of 30 nanometers, achieved by monitoring atomic survival probability as a function of displacement across the waveguide.

Researchers modeled atomic motional states using a truncated harmonic oscillator, accounting for a finite Lamb-Dicke parameter, to calculate survival probability based on scattering rates. The team validated their model with experimental data, achieving good agreement with a predicted decay length and initial atomic temperature. A key innovation is the use of nanophotonic structures, such as waveguides and cavities, to enhance and control the interaction between single atoms and photons, allowing for stronger coupling, increased efficiency, and miniaturization of quantum devices. The core idea involves trapping single Rubidium atoms near nanoscale waveguides or cavities, confining light and dramatically increasing the interaction strength between the atom and photons. This research utilizes cavity quantum electrodynamics and waveguide quantum electrodynamics to modify the vacuum electromagnetic field and mediate interactions between atoms.

The team aims to achieve deterministic interactions between single atoms and single photons, crucial for building quantum gates, and to precisely control the quantum state of the atom for encoding and processing quantum information. This research also explores quantum metrology and sensing, utilizing enhanced atom-photon interactions for improved precision in measurements. The creation of the nanoscale photonic structures requires advanced nanofabrication techniques. The researchers have achieved the strong coupling regime, where the rate of interaction between the atom and the photon is faster than the decay rates of both, a key milestone for quantum optics.

They have demonstrated the ability to generate single photons on demand from a single atom coupled to a waveguide, enhancing the efficiency of single-photon emission for quantum communication and cryptography. The researchers have created entangled states between the atom and the photon, a fundamental resource for quantum information processing, and the atom can serve as a quantum memory, storing quantum information for a certain period of time. The use of waveguides to connect multiple atoms creates a quantum network for distributing quantum information, and the potential to integrate these atom-photon systems with other quantum technologies, such as superconducting circuits, exists. The use of nanophotonics allows for the miniaturization of quantum devices, making them more practical for real-world applications, and enhances precision in measurements due to the strong atom-photon interaction. This research has potential applications in secure quantum communication, powerful quantum computing, highly sensitive quantum sensors, improved precision in quantum metrology, and fundamental tests of quantum mechanics, as well as the development of new imaging techniques with enhanced resolution and sensitivity. In summary, this research represents a significant advance in quantum optics and nanophotonics, paving the way for the development of practical quantum technologies through the unique properties of single atoms and nanoscale photonic structures.

Atomic Lattices Coupled to On-Chip Photonics

This research demonstrates the successful and deterministic coupling of ultracold atomic lattices to light guided within on-chip photonic circuits, establishing a versatile quantum interface between single atoms and integrated photonics. By carefully designing suspended silicon nitride structures and improving light injection efficiency, the team achieved high retention rates during the transport and delivery of single atoms over millimeter distances, bridging free-space atomic arrays with integrated nanophotonic circuits. This precise control opens avenues for advancements in neutral-atom quantum computing and simulation, enabling fast optical readout and efficient light-matter interactions at the nanoscale. The team also showcased the platform’s capabilities as a sensitive probe of nanoscale structures and optical fields.

Single atoms function as natural dipole probes, allowing for in-situ imaging of evanescent fields and three-dimensional scanning microscopy without the risk of sample damage associated with conventional techniques. While acknowledging limitations related to atomic confinement within the traps, the researchers suggest improvements through higher numerical aperture objective lenses and atomic cooling, and highlight the potential for sensing applications including quantum electrometry and the measurement of surface forces. This work establishes a powerful platform for exploring light-matter interactions and developing novel quantum technologies.