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arXiv:1908.03319 · Physical Review Letters

Real-Time Observation of Single Atoms Trapped and Interfaced to a Nanofiber Cavity

K. P. Nayak, 王杰 Wang Jie, Jameesh Keloth

Published Nov 19, 2019• 56 citations
arXivHTMLPDF

Abstract

We demonstrate efficient interfacing of individually trapped single atoms to a nanofiber cavity. The cavity is formed by fabricating photonic crystal structures directly on the nanofiber using femtosecond laser ablation. The single atoms are interfaced to the nanofiber cavity using an optical tweezer based side-illumination trapping scheme. We show that the fluorescence of individual single atoms trapped on the nanofiber cavity can be readily observed in real-time through the fiber guided modes. From the photon statistics measured for different cavity decay rates, the effective coupling rate of the atom-cavity interface is estimated to be 34±2 MHz. This yields a cooperativity of 5.4±0.6 (Purcell factor=6.4±0.6) and a cavity enhanced channeling efficiency as high as 85±2% for a cavity mode with a finesse of 140. The trap lifetime is measured to be 52±5 ms. These results may open new possibilities for deterministic preparation of single atom events for quantum photonics applications on an all-fiber platform.

DOI
10.1103/physrevlett.123.213602

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We demonstrate efficient interfacing of individually trapped single atoms to a nanofiber cavity. The cavity is formed by fabricating photonic crystal structures directly on the nanofiber using femtosecond laser ablation. The single atoms are interfaced to the nanofiber cavity using an optical tweezer based side-illumination trapping scheme. We show that the fluorescence of individual single atoms trapped on the nanofiber cavity can be readily observed in real-time through the fiber guided modes. From the photon statistics measured for different cavity decay rates, the effective coupling rate of the atom-cavity interface is estimated to be 34±2 MHz. This yields a cooperativity of 5.4±0.6 (Purcell factor=6.4±0.6) and a cavity enhanced channeling efficiency as high as 85±2% for a cavity mode with a finesse of 140. The trap lifetime is measured to be 52±5 ms. These results may open new possibilities for deterministic preparation of single atom events for quantum photonics applications on an all-fiber platform.
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.
Abstract We demonstrate a one-dimensional array of single atoms interfaced with an optical nanofiber (ONF) using optical tweezers. Single atoms are deterministically trapped in free space and along a 300 nm diameter ONF with tunable atom number and spacing. Atomic fluorescence is collected into guided modes for real-time detection. The guided fluorescence increases with the number of trapped atoms and shows dependence with inter-atomic spacing. This platform enables fiber-integrated quantum interface for quantum communication and scalable quantum networks.
We report the fabrication of a 1.2 cm long cavity directly on a nanofiber using femtosecond laser ablation. The cavity modes with finesse values in the range of 200-400 can enable the "strong-coupling" regime of cavity QED, with high cooperativity of 10-20, for a single atom trapped 200 nm away from the fiber surface [Phys. Rev. A80, 053826 (2009)PLRAAN1050-294710.1103/PhysRevA.80.053826]. Such cavity modes can still maintain the transmission between 40%-60%, suggesting a one-pass intracavity transmission of 99.53%. Other cavity modes, which can enable cooperativity in the range of 3-10, show transmission over 60%-85% and are suitable for fiber-based single-photon sources and quantum nonlinear optics in the "Purcell" regime.
We demonstrate cavity QED conditions in the Purcell regime for single quantum emitters on the surface of an optical nanofiber. The cavity is formed by combining an optical nanofiber and a nanofabricated grating to create a composite photonic crystal cavity. By using this technique, significant enhancement of the spontaneous emission rate into the nanofiber guided modes is observed for single quantum dots. Our results pave the way for enhanced on-fiber light-matter interfaces with clear applications to quantum networks.
Abstract Recent advances in the coherent control of single quanta of light, photons , is a topic of prime interest, and is discussed under the banner of quantum photonics . In the last decade, the subwavelength diameter waist of a tapered optical fiber, referred to as an optical nanofiber , has opened promising new avenues in the field of quantum optics, paving the way toward a versatile platform for quantum photonics applications. The key feature of the technique is that the optical field can be tightly confined in the transverse direction while propagating over long distances as a guided mode and enabling strong interaction with the surrounding medium in the evanescent region. This feature has led to surprising possibilities to manipulate single atoms and fiber-guided photons, e.g. the efficient channeling of emission from single atoms and solid-state quantum emitters into the fiber-guided modes, high optical depth with a few atoms around the nanofiber, trapping atoms around a nanofiber, and atomic memories for fiber-guided photons. Furthermore, implementing a moderate longitudinal confinement in nanofiber cavities has enabled the strong coupling regime of cavity quantum electrodynamics to be reached, and the long-range dipole–dipole interaction between quantum emitters mediated by the nanofiber offers a platform for quantum nonlinear optics with an ensemble of atoms. In addition, the presence of a longitudinal component of the guided field has led to unique capabilities for chiral light–matter interactions on nanofibers. In this article, we review the key developments of the nanofiber technology toward a vision for quantum photonics on an all-fiber interface.
We present a novel approach to enhance the spontaneous emission rate of single quantum emitters in an optical nanofiber-based cavity by introducing a narrow air-filled groove into the cavity. Our results show that the Purcell factor for single quantum emitters inside the groove of the nanofiber-based cavity can be at least six times greater than for such an emitter on the fiber surface when using an optimized cavity mode and groove width. Moreover, the coupling efficiency of single quantum emitters into the guided mode of this nanofiber-based cavity can reach up to ∼80% with only 35 cavity-grating periods. This new system has the potential to act as an all-fiber platform to realize efficient coupling of photons from single emitters into an optical fiber for quantum information applications.