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Quantum Computing, Communication, and Simulation

Strong interactions between integrated photonics and atomic vapors: towards single-photon-level operation

Roy Zektzer, Xiyuan Lu, Khoi Tuan Hoang, Rahul Shrestha, Sharoon Austin, Feng Lei Zhou, Daron Westly, Paul D. Lett, Alexey Vyacheslavovich Gorshkov, Kartik A. Srinivasan

Published Mar 13, 2024• 0 citations
Publisher

Abstract

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.

DOI
10.1117/12.3001965

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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.
Strong coupling between atomic ensembles and high-quality optical cavities enables collective and nonlinear phenomena that are central to cavity quantum electrodynamics (cQED). Many experiments have been performed on this topic, with most of them focusing on cold atoms. Here, we experimentally demonstrate collective strong coupling between thermal rubidium vapor and high-quality silicon nitride microring resonators (MRRs) on an integrated photonic chip. We observe cavity-mode splitting, with a measured collective coupling strength of g N / 2 π ≈ 1 G Hz and a collective cooperativity of C N ≈ 2 at 110 ∘ C , indicating coherent energy exchange between the atomic ensemble and the cavity mode despite rapid decoherence in the thermal vapor system. We infer an average of 20 atoms effectively participating in the collective interaction, yielding a single-atom cooperativity of C 0 = 0.1 and approaching the single-atom strong-coupling regime. Our results establish the integrated thermal vapor MRR platform as a robust, compact, and scalable system for studying collective and nonlinear phenomena in cQED.
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.
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.
Abstract The miniaturization of atomic quantum systems and their integration into silicon microchips paves the way for a wide variety of applications in quantum computing, metrology and magnetometry. A particular interest is found in the integration of quantum entities into the micro and nanoscale photonic resonators to implement chip scale cavity quantum electrodynamics. Here we demonstrate the interaction of a chip scale micro disc resonator with thermal rubidium atoms via the evanescent field of the mode. We observe high Rabi splitting of 4 GHz in the transmission spectrum of the coupled photonic-atomic system due to collective enhancement of the coupling rate by the ensemble of hot atoms and present a theoretical model to support the measured results. This result corresponds to atom-photon cooperativity of ~ 1. Such cooperativity is the onset for quantum interference, needed for high-end chip scale quantum technologies, such as such as quantum manipulation, quantum information storage and processing, and few photon switching.
In this work, we propose performing key operations in quantum computation and communication using room-temperature atoms moving across a grid of high-quality-factor, small-mode-volume cavities. These cavities enable high-cooperativity interactions with single atoms to be achieved with a characteristic timescale much shorter than the atomic transit time, allowing multiple coherent operations to take place. We study scenarios where we can drive a Raman transition to generate photons with specific temporal shapes and to absorb, and hence detect, single photons. The strong atom-cavity interaction can also be used to implement the atom-photon controlled-phase gate, which can then be used to construct photon-photon gates, create photonic cluster states, and perform nondemolition detection of single photons. We provide numerics validating our methods and discuss the implications of our results for several applications.