Fiber ring resonator with a nanofiber section for chiral cavity quantum electrodynamics and multimode strong coupling

Abstract

We experimentally realize an optical fiber ring resonator that includes a tapered section with subwavelength-diameter waist. In this section, the guided light exhibits a significant evanescent field which allows for efficient interfacing with optical emitters. A commercial tunable fiber beam splitter provides simple and robust coupling to the resonator. Key parameters of the resonator such as its out-coupling rate, free spectral range, and birefringence can be adjusted. Thanks to the low taperand coupling-losses, the resonator exhibits an unloaded finesse of F = 75 ± 1, sufficient for reaching the regime of strong coupling for emitters placed in the evanescent field. The system is ideally suited for trapping ensembles of laser-cooled atoms along the nanofiber section. Based on measured parameters, we estimate that the system can serve as a platform for optical multimode strong coupling experiments. Finally, we discuss the possibilities of using the resonator for applications based on chiral quantum optics.Over the past years, significant research effort has been devoted to interfacing quantum emitters, such as molecules, quantum dots, color centers, and neutral atoms, with fiber-guided light fields. Suitable lightmatter interfaces are considered to be key elements for future quantum networks [1]. One way to realize such an interface consists in coupling emitters to the evanescent fields surrounding the nanofiber-waist of a tapered optical fiber, i.e., a fiber section with sub-wavelength diameter. Such systems already provide absorption probabilities for single fiber-guided photons of about 25 % for a single emitter located on the nanofiber surface [2] and about 5 % at a distance of 200 nm, typical for cold atoms in nanofiber-based optical dipole traps [3,4].One way to further enhance the light-matter coupling strength is to increase the number of emitters in the evanescent field and to take advantage of their collective coupling. Another option relies on confining the light in an optical resonator, which allows one to even reach the regime of strong coupling in the sense of cavity quantum electrodynamics (CQED) [5]. There, coherent emitterlight interaction strength dominates over the incoherent decay channels. In this context, optical nanofibers are a versatile platform as they allow one to combine both approaches and, in this way, to reach very strong lightmatter coupling in an fiber-integrated environment.Different nanofiber-based Fabry-Pérot resonator schemes have been developed, e.g., based on Bragg structures created using ion beam milling [6] Here, we demonstrate a tapered fiber-based ring resonator with optical characteristics that are compatible with entering the regime of single-atom strong coupling. We experimentally reach a resonator finesse of F = 75 ± 1 which corresponds to a single-atom cooperativity of C ≈ 1. Our implementation offers easy tuning of the resonator eigenpolarizations and out-coupling rate as well as straightforward adjustment of the resonator's free spectral range. Our system is co...

Fabrication and characterization of optical nanofiber interferometer and resonator for the visible range

“…For example, the nanofiber cavity with two fiber Bragg gratings [19] has a mode volume of about 2.6×10 4 μm 3 . The nanofiber cavity with fiber beam splitter gives a big mode volume according to the cavity length of more than two meters [20]. The nanofiber Bragg cavity has the smallest mode volume among the achieved methods for nanofiber based cavity [14], the mode volume is 1 μm 3 , which is achieved with a fabrication process far more demanding than ours.…”

Dynamical creation and detection of entangled many-body states in a chiral atom chain

“…just like in figure 2, the unguided modes remove the pure dimerized steady state, which now is probed dynamically through fluctuations, like in the homogeneous detuning scenario. Finally we remark, that the coupling strength between the quantum emitters and the guided modes can be controlled by employing a cavity, as showed in [40], or by considering a photonic crystal waveguide integrated with solid-state emitters, as shown in [41]. Here, the chiral interaction is obtained in presence of slow-light, together with a strong Purcell enhancement.…”

“…The ability to interface quantum emitters with optical systems opens novel routes for investigating nonequilibrium phenomena in open condensed matter physics [1] and provides, potentially, a platform to perform quantum information processing [2][3][4][5][6][7]. In recent years, the open quantum dynamics of chiral systems, where the emission of photons into a waveguide presents a broken left-right symmetry, has been the object of intense investigation [8][9][10][11][12][13][14][15]. This propagation-direction-dependent light-matter interaction has been observed in a variety of systems, for instance atoms coupled to the evanescent field of a waveguide [16] or a photonic crystal [17][18][19], and quantum dots in photonic nano-structures [20].…”

Cavity QED based on room temperature atoms interacting with a photonic crystal cavity: a feasibility study

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