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Cavity-free efficient coupling between emitters and guided modes is of great current interest for nonlinear quantum optics as well as efficient and scalable quantum information processing. In this work, we extend these activities to the coupling of organic dye molecules to a highly confined mode of a nanofiber, allowing mirrorless and low-threshold laser action in an effective mode volume of less than 100 femtoliters. We model this laser system based on semi-classical rate equations and present an analytic compact form of the laser output intensity. Despite the lack of a cavity structure, we achieve a coupling efficiency of the spontaneous emission to the waveguide mode of 0.07(0.01), in agreement with our calculations. In a further experiment, we also demonstrate the use of a plasmonic nanoparticle as a dispersive output coupler. Our laser architecture is promising for a number of applications in optofluidics and provides a fundamental model system for studying nonresonant feedback stimulated emission.
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Optical high-finesse cavities are a well-known mean to enhance light-matter interactions. Despite large progress in the realization of strongly coupled light-matter systems, the controlled positioning of single solid emitters in cavity modes remains a challenge. We pursue the idea to use nanofibers with sub-wavelength diameter as a substrate for such emitters. This paper addresses the question how strongly optical nanofibers influence the cavity modes. We analyze the influence of the fiber position for various fiber diameters on the finesse of the cavity and on the shape of the modes.
Linearly polarized light can exert a torque on a birefringent object when passing through it. This phenomena, present in Maxwells equations, was revealed by Poynting and beautifully demonstrated in the pioneer experiments of Beth and Holbourn. Modern uses of this effect lie at the heart of optomechanics with angular momentum exchange between light and matter. A milestone of controlling movable massive objects with light is the reduction of their mechanical fluctuations, namely cooling. Optomechanical cooling has been implemented through linear momentum transfer of the electromagnetic field in a variety of systems, but remains unseen for angular momentum transfer to rotating objects. We present the first observation of cooling in a rotational optomechanical system. Particularly, we reduce the thermal noise of the torsional modes of a birefringent optical nanofiber, with resonant frequencies near 200 kHz and a Q-factor above $mathbf{2times10^4}$. Nanofibers are centimeter long, sub-micrometer diameter optical fibers that confine propagating light, reaching extremely large intensities, hence enhancing optomechanical effects. The nanofiber is driven by a propagating linearly polarized laser beam. We use polarimetry of a weak optical probe propagating through the nanofiber as a proxy to measure the torsional response of the system. Depending on the polarization of the drive, we can observe both reduction and enhancement of the thermal noise of many torsional modes, with noise reductions beyond a factor of two. The observed effect opens a door to manipulate the torsional motion of suspended optical waveguides in general, expanding the field of rotational optomechanics, and possibly exploiting its quantum nature for precision measurements in mesoscopic systems.
Vectorially structured light has emerged as an enabling tool in many diverse applications, from communication to imaging, exploiting quantum-like correlations courtesy of a non-separable spatially varying polarization structure. Creating these states at the source remains challenging and is presently limited to two-dimensional vectorial states by customized lasers. Here we invoke ray-wave duality in a simple laser cavity to produce polarization marked multi-path modes that are non-separable in three degrees of freedom and in eight dimensions. As a topical example, we use our laser to produce the complete set of Greenberger-Horne-Zeilinger (GHZ) basis states, mimicking high-dimensional multi-partite entanglement with classical light, which we confirm by a new projection approach. We offer a complete theoretical framework for our laser based on SU(2) symmetry groups, revealing a rich parameter space for further exploitation. Our approach requires only a conventional laser with no special optical elements, is easily scaleable to higher dimensions, and offers a simple but elegant solution for at-the-source creation of classically entangled states of structured light, opening new applications in simulating and enhancing high-dimensional quantum systems.
We demonstrate the fabrication of ultra-low-loss, all-fiber Fabry-Perot cavities containing a nanofiber section, optimized for cavity quantum electrodynamics. By continuously monitoring the finesse and fiber radius during fabrication of a nanofiber between two fiber Bragg gratings, we are able to precisely evaluate taper transmission as a function of radius. The resulting cavities have an internal round-trip loss of only 0.31% at a nanofiber waist radius of 207 nm, with a total finesse of 1380, and a maximum expected internal cooperativity of $sim$ 1050 for a cesium atom on the nanofiber surface. Our ability to fabricate such high-finesse nanofiber cavities may open the door for the realization of high-fidelity scalable quantum networks.
We propose a novel supersymmetry-inspired scheme for achieving robust single mode lasing in arrays of coupled microcavities, based on factorizing a given array Hamiltonian into its supercharge partner array. Pumping a single sublattice of the partner array preferentially induces lasing of an unpaired zero mode. A chiral symmetry protects the zero mode similar to 1D topological arrays, but it need not be localized to domain walls or edges. We demonstrate single mode lasing over a wider parameter regime by designing the zero mode to have a uniform intensity profile.
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