Cavity quantum electrodynamics (cQED), the interaction of a two-level system with a high quality factor ( Q ) cavity, is a foundational building block in different architectures for quantum computation, communication, and metrology. The strong interaction between the atom and the cavity enables single-photon operation, which is required for quantum gates and sources. Cold atoms, quantum dots, and color centers in crystals are among the systems that have shown single-photon operations, but they require significant physical infrastructure. Atomic vapors, on the other hand, require limited experimental infrastructure and are hence much easier to deploy outside a laboratory, but they consist of an ensemble of moving atoms that results in short interaction times involving multiple atoms, which can hamper quantum operations. A solution to this issue can be found in nanophotonic cavities, where the optical mode is confined to a small volume and light-matter interaction is enhanced, so that fast single-atom, single-photon operations are enabled. In this work, we study the interaction of an atomically clad microring resonator (ACMRR) with different-sized ensembles of Rb atoms. We demonstrate strong coupling between an ensemble of ≈50 atoms interacting with a high quality factor ( Q =4.3×10 5 ) ACMRR, yielding a many-atom cooperativity C =(5.5±0.3). We continue to observe signatures of atom-photon interaction for a few (<3) atoms, for which we observe saturation at the level of a few intracavity photons. Further development of our platform, which includes integrated thermo-optic heaters to enable cavity tuning and stabilization, should enable the observation of interactions between single photons and single atoms.
We present recent results aiming to construct single photon sources, detectors and gates using the integration of hot Rubidium atoms and microring resonators (MRRs). We demonstrate strong coupling between an ensemble of ≈53 atoms interacting with a high-Q (>4x10^5) cavity mode, with a many-atom coupling strength g/2pi≈1 GHz and cooperativity C≈3.6 achieved. A peak single-atom cooperativity C0≈0.4 is inferred; to achieve higher cooperativity, we have developed defect mode photonic crystal ring resonators with a 10x reduction in mode volume compared to the MRR while maintaining Q>10^5. Finally, we will discuss theoretical results that support single photon operations using these devices.
We present a complete fabrication study of an efficiently coupled microring optical circuit tailored for cavity quantum electrodynamics with trapped atoms. The microring structures are fabricated on a transparent membrane with high in-vacuum fiber edge-coupling efficiency in a broad frequency band. In addition, a bus waveguide pulley coupler realizes critical coupling to the microrings at both of the cesium D-line frequencies, while high coupling efficiency is achieved at the cesium “magic” wavelengths for creating a lattice of two-color evanescent field traps above a microring. The presented platform holds promise for realizing a robust atom-nanophotonics hybrid quantum device.
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.