We study the cross-sectional profiles and spatial distributions of the fields in guided normal modes of two coupled parallel optical nanofibers. We show that the distributions of the components of the field in a guided normal mode of two identical nanofibers are either symmetric or antisymmetric with respect to the radial principal axis and the tangential principal axis in the cross-sectional plane of the fibers. The symmetry of the magnetic field components with respect to the principal axes is opposite to that of the electric field components. We show that, in the case of even $\mathcal{E}_z$-cosine modes, the electric intensity distribution is dominant in the area between the fibers, with a saddle point at the two-fiber center. Meanwhile, in the case of odd $\mathcal{E}_z$-sine modes, the electric intensity distribution at the two-fiber center attains a local minimum of exactly zero. We find that the differences between the results of the coupled mode theory and the exact mode theory are large when the fiber separation distance is small and either the fiber radius is small or the light wavelength is large. We show that, in the case where the two nanofibers are not identical, the intensity distribution is symmetric about the radial principal axis and asymmetric about the tangential principal axis.
We demonstrate ladder-type electromagnetically induced transparency (EIT) using an optical nanofiber suspended in a warm rubidium vapor. The signal and control fields are both guided along the nanofiber, which enables strong nonlinear interactions with the surrounding atoms at relatively low powers. Transit-time broadening is found to be a significant EIT decoherence mechanism in this tightly-confined waveguiding geometry. Nonetheless, we observe significant EIT and controlled polarization rotation using control-field powers of only a few microWatts in this relatively robust warm-atom nanofibe…
We experimentally demonstrate the efficient channeling of fluorescence photons from single q-dots on optical nanofiber into the guided modes, by measuring the photon-count rates through the guided and radiation modes simultaneously. We obtain the maximum channeling efficiency to be 22.0 (\pm4.8)% at fiber diameter of 350 nm for the emission wavelength of 780 nm. The results may open new possibilities in quantum information technologies for generating single photons into single-mode optical-fibers.
We calculate analytically and numerically the axial orbital and spin torques of guided light on a two-level atom near an optical nanofiber. We show that the generation of these torques is governed by the angular momentum conservation law in the Minkowski formulation. The orbital torque on the atom near the fiber has a contribution from the average recoil of spontaneously emitted photons. Photon angular momentum and atomic spin angular momentum can be converted into atomic orbital angular momentum. The orbital and spin angular momenta of the guided field are not transferred separately to the or…
We demonstrate a bright and polarized fiber in-line single photon source based on plasmon-enhanced emission of colloidal single quantum dots into an optical nanofiber. We show that emission properties of single quantum dots can be strongly enhanced in the presence of single gold nanorods leading to a bright and strongly polarized single photon emission. The single photons are efficiently coupled to guided modes of the nanofiber and eventually to a single mode optical fiber. The brightness (fiber-coupled photon count rate) of the single photon source is estimated to be 12.2(0.6) MHz, with high …
We report the experimental observation of slow-light and coherent storage in a setting where light is tightly confined in the transverse directions. By interfacing a tapered optical nanofiber with a cold atomic ensemble, electromagnetically induced transparency is observed and light pulses at the single-photon level are stored in and retrieved from the atomic medium with an overall efficiency of (10 +/- 0.5) %. Collapses and revivals can be additionally controlled by an applied magnetic field. Our results based on subdiffraction-limited optical mode interacting with atoms via the strong evanes…
We study the optical force between two coupled parallel identical nanofibers using the rigorous array mode theory. We show that the forces of the even array modes are attractive, while the forces of the odd array modes are repulsive. We examine the dependencies of the optical forces on the array mode type, the fiber radius, the light wavelength, and the fiber separation distance. We show that, for a given power and a given separation distance, the absolute value of the force achieves a peak when the fiber radius and the light wavelength are appropriate.
We study the propagation of guided light along an array of three-level atoms in the vicinity of an optical nanofiber under the condition of electromagnetically induced transparency. We examine two schemes of atomic levels and field polarizations where the guided probe field is quasilinearly polarized along the major or minor principal axis, which is parallel or perpendicular, respectively, to the radial direction of the atomic position. Our numerical calculations indicate that 200 cesium atoms in a linear array with a length of 100 $μ$m at a distance of 200 nm from the surface of a nanofiber w…
We calculate the force of a quasicircularly polarized guided light field of a nanofiber on a dielectric spherical particle. We show that the orbital parts of the axial and azimuthal components of the Poynting vector are always positive while the spin parts can be either positive or negative. We find that, for appropriate values of the size parameter of the particle, the azimuthal component of the force is directed oppositely to the circulation direction of the energy flow around the nanofiber. The occurrence of such a negative azimuthal force indicates that the particle undergoes a negative to…
We study the propagation of nanofiber-guided light through an array of atomic cesium, taking into account the transitions between the hyperfine levels $6S_{1/2}F=4$ and $6P_{3/2}F'=5$ of the $D_2$ line. We derive the coupled-mode propagation equation, the input-output equation, the scattering matrix, the transfer matrix, and the reflection and transmission coefficients for the guided field in the linear, quasistationary, weak-excitation regime. We show that, when the initial distribution of populations of atomic ground-state sublevels is flat, the quasilinear polarizations along the principal …
We study the scattering of guided light from a multilevel cesium atom with the transitions between the hyperfine levels $6S_{1/2}F=4$ and $6P_{3/2}F'=5$ of the $D_2$ line into the guided modes of a nanofiber. We show that the rate of scattering of guided light from the atom in the steady-state regime into the guided modes is asymmetric with respect to the forward and backward directions and depends on the polarization of the probe field. The asymmetry between the forward and backward scattering is a result of the complex transition structure of the atom and the existence of a longitudinal comp…
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. 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.
We study the coupling between the fundamental guided modes of two identical parallel nanofibers analytically and numerically. We calculate the coefficients of directional coupling, butt coupling, and mode energy changes as functions of the fiber radius, the light wavelength, and the fiber separation distance. We show that, due to the symmetry of the system, a mode of a nanofiber with the principal quasilinear polarization aligned along the radial or tangential axis is coupled only to the mode with the same corresponding principal polarization of the other nanofiber. We find that the effects of…
We fabricate an extremely thin optical fiber that supports a super-extended mode with a diameter as large as 13 times the optical wavelength, residing almost entirely outside the fiber and guided over thousands of wavelengths (5 mm), in order to couple guided light to warm atomic vapor. This unique configuration balances between strong confinement, as evident by saturation powers as low as tens of nW, and long interaction times with the thermal atoms, thereby enabling fast and coherent interactions. We demonstrate narrow coherent resonances (tens of MHz) of electromagnetically induced transpar…
We theoretically investigate measurement-based feedback control of a laser-driven one-dimensional atomic chain interfaced with a nanofiber. The interfacing leads to all-to-all interactions among the atomic emitters and induces chirality, i.e. the directional emission of photons into a preferred guided mode of the nanofiber. In the setting we consider, the measurement of guided light -- conducted either by photon counting or through homodyne detection of the photocurrent quadratures -- is fed back into the system through a modulation of the driving laser field. We investigate how this feedback …
We study the strong coupling between photons and atoms that can be achieved in an optical nanofiber geometry when the interaction is dispersive. While the Purcell enhancement factor for spontaneous emission into the guided mode does not reach the strong-coupling regime for individual atoms, one can obtain high cooperativity for ensembles of a few thousand atoms due to the tight confinement of the guided modes and constructive interference over the entire chain of trapped atoms. We calculate the dyadic Green's function, which determines the scattering of light by atoms in the presence of the fi…
Optical interfaces for quantum emitters are a prerequisite for implementing quantum networks. Here, we couple single molecules to the guided modes of an optical nanofiber. The molecules are embedded within a crystal that provides photostability and, due to the inhomogeneous broadening, a means to spectrally address single molecules. Single molecules are excited and detected solely via the nanofiber interface without the requirement of additional optical access. In this way, we realize a fully fiber-integrated system that is scalable and may become a versatile constituent for quantum hybrid sys…
Tapered optical fibers with a nanofiber waist are widely used tools for efficient coupling of light to photonic devices or quantum emitters via the nanofiber's evanescent field. In order to ensure well-controlled coupling, the phase and polarization of the nanofiber guided light field have to be stable. Here, we show that in typical tapered optical fibers these quantities exhibit high-frequency thermal fluctuations. They originate from high-Q torsional oscillations that opto-mechanically couple to the nanofiber-guided light. We present a simple ab-initio theoretical model that quantitatively e…
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 a…
We propose a novel platform for the investigation of quantum wave packet dynamics, offering a complementary approach to existing theoretical models and experimental systems. It relies on laser-cooled neutral atoms which orbit around an optical nanofiber in an optical potential produced by a red-detuned guided light field. We show that the atomic center-of-mass motion exhibits genuine quantum effects like collapse and revival of the atomic wave packet. As distinctive advantages, our approach features a tunable dispersion relation as well as straightforward readout for the wave packet dynamics a…
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 taper- and coupling-losses, the resonator exhibits an unloaded finesse of F=75+/-1, sufficient for reaching…
We experimentally and theoretically investigate collective radiative effects in an ensemble of cold atoms coupled to a single-mode optical nanofiber. Our analysis unveils the microscopic dynamics of the system, showing that collective interactions between the atoms and a single guided photon gradually build-up along the atomic array in the direction of propagation of light. These results are supported by time-resolved measurements of the light transmitted and reflected by the ensemble after excitation via nanofiber-guided laser pulses, whose rise and fall times are shorter than the atomic life…
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 located inside the groove of the nanofiber-based cavity can be at least six times greater than that 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 $\sim$ 80 $\%$ …
We demonstrate an optical tweezer based single atom trapping on an optical nanofiber cavity. We show that the fluorescence of single atoms trapped on the nanofiber cavity can be readily observed in real-time through the fiber guided modes. The photon correlation measurements further clarify the atom number and the dynamics of the trap. The trap lifetime is measured to be 52$\pm$5 ms. From the photon statistics measured for different cavity decay rates, the effective coupling rate of the atom-cavity interface is estimated to be 34$\pm$2 MHz. This yields a cooperativity of 5.4$\pm$0.6 and a cavi…
We propose a method of trapping atoms in arrays near to the surface of a composite nanophotonic device with optimal coupling to a single cavity mode. The device, comprised of a nanofiber mounted on a grating, allows the formation of periodic optical trapping potentials near to the nanofiber surface along with a high cooperativity nanofiber cavity. We model the device analytically and find good agreement with numerical simulations. We numerically demonstrate that for an experimentally realistic device, an array of traps can be formed whose centers coincide with the antinodes of a single cavity …
We report on the observation of a Zeeman shift (order of 100 MHz) of the Doppler-broadened D2 transition of both 85Rb and 87Rb isotopes via transmission through a tapered optical nanofiber in the presence of a DC magnetic field. Linearly-polarized light propagating in the nanofiber is analyzed as a superposition of two orthogonally circularly-polarized orientations, σ+ and σ-. In the absence of the magnetic field, the absorption of these polarizations by the atomic vapor, via the evanescent field at the waist of the nanofiber, is degenerate. When a weak magnetic field is applied parallel to th…
We demonstrate a fiber in-line single photon source based on a hybrid system of colloidal single quantum dots deposited on an optical nanofiber and cooled down to cryogenic temperature (3.7 K). We show that a charged state (trion) of the single quantum dot exhibits a photo-stable emission of single photons with high quantum efficiency, narrow linewidth (3 meV FWHM) and fast decay time ($10.0\pm0.5$ ns). The single photons are efficiently coupled to the guided modes of the nanofiber and eventually to a single mode optical fiber. The brightness (efficiency) of the single photon source is estimat…
We experimentally demonstrate optical trapping of 87Rb atoms using a two-color evanescent field around an optical nanofiber. In our trapping geometry, a blue-detuned traveling wave whose polarization is nearly parallel to the polarization of a red-detuned standing wave produces significant vector light shifts that lead to broadening of the absorption profile of a near-resonant beam at the trapping site. A model that includes scalar, vector, and tensor light shifts of the probe transition $5S_{1/2}$-$5P_{3/2}$ from the trapping beams, weighted by the temperature-dependent position of the atoms …
This thesis covers different subjects of nonlinear and quantum optics, studied in systems with scales smaller or com-parable to the wavelength of interest. The manuscript is divided into two parts. The first part of the manuscript dealswith several applications of optical nanofibers as a platform for light-matter interaction. In particular we will explore: thecoupling between a dipole placed on the surface of the nanofiber; the coupling between two parallel nanofibers; as well asthe mechanical properties of an optical nanofiber. In the second part of the manuscript, we will focus on solving tw…
We study the transverse spin angular momentum of fiber eigenmodes. As an intrinsic property of fiber eigenmodes, it becomes considerable in optical nanofibers and, especially, increases sharply in the evanescent field. We derive analytical expressions of this angular momentum, and present its density distribution inside andoutside nanofibers. Significantly, we find the optimal ratio of the fiber core radius to the wavelength to obtain the maximum surface transverse spin. For instance, the optimal fiber radius is one fourth of the wavelength for the fundamental mode. Furthermore, we investigate…
Quantum control of atoms at ultrashort distances from surfaces would open a new paradigm in quantum optics and offer a novel tool for the investigation of near-surface physics. Here, we investigate the motional states of atoms that are bound weakly to the surface of a hot optical nanofiber. We theoretically demonstrate that with optimized mechanical properties of the nanofiber these states are quantized despite phonon-induced decoherence. We further show that it is possible to influence their properties with additional nanofiber-guided light fields and suggest heterodyne fluorescence spectrosc…
A bright source of fiber-coupled, polarized single photons is an essential component of any realistic quantum network based on today's existing fiber infrastructure. Here, we develop a Purcell enhanced, polarized source of single photons at room temperature by coupling single colloidal quantum dots to the localized surface plasmon-polariton modes of single gold nanorods, combined on the surface of an optical nanofiber. A maximum enhancement of photon emission of 62 times was measured corresponding to a degree of polarization of 86 $\%$, and a brightness enhancement of four times in the fiber m…
A fundamental building block for on-chip quantum photonics is a single-photon source with high repetition rates, which can enable many applications such as high-speed quantum communication and quantum information processing. Ideally, such single photon sources would then require a large on-chip photon extraction decay rate, namely the rate of excited photons coupled into nanofibers or waveguides, over a broad spectral range. However, this goal has remained elusive till date. Here we propose a feasible scheme to enhance the on-chip photon extraction decay rate of quantum emitters, through the t…
We report three orders of magnitude optical cooling of the fundamental torsional mode of a 5 mm-long, 550 nm diameter optical nanofiber. The rotation of the nanofiber couples to the polarization of guided laser fields. We use a weak laser probe to monitor the rotation, and use feedback to modulate the polarization of an auxiliary drive laser providing torque. Our results present a tool for the optomechanical control of large-scale torsional resonators, with metrological applications and potential implications for studying macroscopic objects in quantum states.
We study the enhancement of cooperativity in the atom-light interface near a nanophotonic waveguide for application to quantum nondemolition (QND) measurement of atomic spins. Here the cooperativity per atom is determined by the ratio between the measurement strength and the decoherence rate. Counterintuitively, we find that by placing the atoms at an azimuthal position where the guided probe mode has the lowest intensity, we increase the cooperativity. This arises because the QND measurement strength depends on the interference between the probe and scattered light guided into an orthogonal p…
Optical nanofibres are used to confine light to subwavelength regions and are very promising tools for the development of optical fibre-based quantum networks using cold, neutral atoms. To date, experimental studies on atoms near nanofibres have focussed on fundamental fibre mode interactions. In this work, we demonstrate the integration of a few-mode optical nanofibre into a magneto-optical trap for $^{87}$Rb atoms. The nanofibre, with a waist diameter of $\sim$700 nm, supports both the fundamental and first group of higher order modes and is used for atomic fluorescence and absorption studie…
Optical waveguides in the form of glass fibers are the backbone of global telecommunication networks. In such optical fibers, the light is guided over long distances by continuous total internal reflection which occurs at the interface between the fiber core with a higher refractive index and the lower index cladding. Although this mechanism ensures that no light escapes from the waveguide, it gives rise to an evanescent field in the cladding. While this field is protected from interacting with the environment in standard optical fibers, it is routinely employed in air- or vacuum-clad fibers i…
A nanostructured chalcogenide-metal optical fiber is proposed. This hybrid nanofiber is embedded with a periodic array of triangular-shaped deep-subwavelength metallic nanowires set up in a bowtie configuration. Our simulations show that the proposed nanostructured fiber supports a guided collective plasmonic mode enabling both subwavelength field confinement and extreme nonlinear light- matter interactions, much larger than a bare chalcogenide nanowire of comparable diameter. This is all achieved with less than 3% by volume of metal content.
Optical fibers confine and guide light almost unattenuated and thus convey light forces to polarizable nano-particles over very long distances. Radiation pressure forces arise from scattering of guided photons into free space while gradient forces are based on coherent scattering between different fiber modes or propagation directions. Interestingly, even scattering between co-propagating modes induces longitudinal forces as the transverse confinement of the light modes creates mode dependent longitudinal wave-vectors and photon momenta. We generalize a proven scattering matrix based approach …
