Interfacing cold atoms with nanoscopic dielectric devices offers exciting opportunities for quantum technologies. We focus on enhancing light-matter coupling via slow-mode nanophotonic crystals while addressing challenges in design, nanofabrication, and precise atom delivery near surfaces.

We demonstrate an approach for routing guided single photons by combining atom trapping and transverse light con-finement with an optical nanofiber. The direction of photon propagation, either reflection or transmission, is controlled by a femtojoule-level beam.

Novel platforms interfacing trapped cold atoms and guided light in nanoscale waveguides are a promising route to achieve a regime of strong coupling between light and atoms in single pass, with applications to quantum non-linear optics and quantum simulation. A strong challenge for the experimental development of this emerging waveguide-QED field of research is to combine facilitated optical access for atom transport, atom trapping via guided modes and robustness to inherent nanofabrication imperfections. In this endeavor, here we propose to interface Rubidium atoms with a photonic-crystal waveguide based on a large-index GaInP slab. With a specifically tailored half-W1 design, we show that a large chiral coupling to the waveguide can be obtained and guided modes can be used to form two-color dipole traps for atoms at 116~nm from the edge of the structure. This optimized device should greatly improve the level of experimental control and facilitate the atom integration.

Interfacing cold neutral atoms and photons guided in nanoscale waveguides has raised a large interest over the recent years, with a wealth of emerging opportunities. Arrays of atoms can be trapped in the evanescent field of guided modes and the strong transverse confinement enables to increase the individual atom-photon coupling in single pass. Remarkable experimental advances have been obtained with optical nanofibers [1], but photonic crystals waveguides (PCW) are very promising as they allow for precise dispersion engineering. Despite these promises, trapping atoms in the vicinity of such PCWs is still at its infancy.

Coupling quantum emitters and nanostructures, in particular cold atoms and waveguides, has recently raised a large interest due to unprecedented possibilities of engineering light-matter interactions. However, the implementation of these promising concepts has been hampered by various theoretical and experimental issues. In this work, we propose a new type of periodic dielectric waveguide that provides strong interactions between atoms and guided photons with an unusual dispersion. We design an asymmetric comb waveguide that supports a slow mode with a quartic (instead of quadratic) dispersion and an electric field that extends far into the air cladding for an optimal interaction with atoms. We compute the optical trapping potential formed with two guided modes at frequencies detuned from the atomic transition. We show that cold Rubidium atoms can be trapped as close as 100 nm from the structure in a 1.3-mK-deep potential well. For atoms trapped at this position, the emission into guided photons is largely favored, with a beta factor as high as 0.88 and a radiative decay rate into the slow mode 10 times larger than the free-space decay rate.

Trapping cold neutral atoms in close proximity to nanostructures has raised a large interest in recent years, pushing the frontiers of cavity-QED and boosting the emergence of the waveguide-QED field of research. The design of efficient dipole trapping schemes in evanescent fields is a crucial requirement and a difficult task. Here we present an open-source Python package for calculating optical trapping potentials for neutral atoms, especially in the vicinity of nanostructures. Given field distributions and for a variety of trap configurations, nanotrappy computes the three-dimensional trapping potentials as well as the trap properties, ranging from trap positions to trap frequencies and state-dependent light shifts. We demonstrate the versatility for various seminal structures in the field, e.g., optical nanofiber, alligator slow-mode photonic-crystal waveguide, and microtoroid. This versatile package facilitates the systematic design of structures and provides a full characterization of trapping potentials with applications to the coherent manipulation of atoms and quantum information science.

We present a proposal for trapping Rubidium cold atoms near a novel design of a GaInP photonic crystal waveguide with characteristics optimized through systematic and inverse design. Purcell factors higher than unity are predicted.

Reaching a regime of strong coupling between light and atoms is a long-sought goal in quantum optics, as it will enable non-linear optics at the photon level. Interfacing atoms with guided light in nanophotonic waveguides is a promising route to achieve such regimes. Experimental platforms include nanofibers [1] and photonic crystal waveguides (PCWs), owing to the large transverse confinement of their guided modes. With PCWs, tuning the dispersion relation gives rise to the additional benefit of a very low group velocity of the guided light [2] , allowing for strong coupling even in single pass. Moreover these systems can help explore waveguide-QED and probe exciting novel bandgap physics [3] . While encouraging values of couplings have been observed with first corrugated devices [4] , a photonic platform with trapped atoms via guided modes in the vicinity of a waveguide and lying deep in the strong coupling regime has yet to be demonstrated.

Nanoscale waveguides provide a tight transverse confinement of guided light, not limited by the Rayleigh range, allowing enhanced atom-photon interaction over a large sample. In our system, we interface a tapered optical nanofiber with an ensemble of cold Cesium atoms in an ultra-high vacuum chamber, trapped in a 1D lattice geometry using the evanescent field around the nanofiber.

We report storage and retrieval of a single collective excitation of an atomic ensemble coupled to an optical nanofiber. We further provide theoretical and experimental advances on controllable atomic Bragg mirrors and atomic cavity systems.

Ordered atomic arrays trapped in the vicinity of nanoscale waveguides offer original light-matter interfaces, with applications to quantum information and quantum non-linear optics. Here, we study the decay dynamics of a single collective atomic excitation coupled to a waveguide in different configurations. The atoms are arranged as a linear array and only a segment of them is excited to a superradiant mode and emits light into the waveguide. Additional atomic chains placed on one or both sides play a passive role, either reflecting or absorbing this emission. We show that when varying the geometry, such a one-dimensional atomic system could be able to redirect the emitted light, to directionally reduce or enhance it, and in some cases to localize it in a cavity formed by the atomic mirrors bounding the system.

We propose a method to continuously frequency shift a target laser that is frequency stabilized by a reference laser, which is several hundreds of nanometers detuned. We demonstrate the technique using the 5S 1/2 to 5P 3/2 to 29D 5/2 Rydberg transition in 87Rb vapor and lock the 482 nm target laser to the 780 nm reference laser using the cascaded electromagnetically induced transparency signal. The stabilized frequency of the target laser can be shifted by about 1.6 GHz by phase modulating the reference laser using a waveguide-type electro-optical modulator. This simple method for stable frequency shifting can be used in atomic or molecular physics experiments that require a laser frequency scanning range on the order of several GHz.

We develop a theoretical framework for spin selection in single-frequency two-photon excitation of alkali-metal atoms as a function of polarization of the excitation light. We verify the theory by experimentally probing the 5S(1/2) -> 6S(1/2) transition rate in Rb-87 in two configurations: paraxial light excitation of warm vapor and nonparaxial excitation of laser-cooled atoms. The transition rate follows a quadratic dependence on the helicity parameter linked to the excitation light's polarization. For paraxial excitation, the transition rate scales as the squared degree of linear polarization, being zero for circularly polarized light. In contrast, for nonparaxial excitation via an optical nanofiber, the two-photon transition is not completely extinguished by varying the light polarization. Our findings lead to a deeper and more universal understanding of the physics of multiphoton processes in atoms.

We report on a controllable, hybrid quantum system consisting of cold Rydberg atoms and an optical nanofiber interface. Using a two-photon ladder-type excitation in Rb-87, we demonstrate both coherent and incoherent Rydberg excitation at submicron distances from the nanofiber surface. The 780-nm photon, near resonant to the 5S -> 5P transition, is mediated by the cooling laser, while the 482-nm light, near resonant to the 5P -> 29D transition, is mediated by the guided mode of the nanofiber. The population loss rate of the cold atom ensemble is used to measure the Rydberg population rate. A theoretical model is developed to interpret the results and link the population loss rate to the experimentally measured, effective Rabi frequency of the process. This work makes headway in the study of Rydberg atom-surface interactions at submicron distances and the use of cold Rydberg atoms for all-fibered quantum networks.

Light guided by an optical nanofibre has a very steep evanescent field gradient extending from the fibre surface. This gradient can be exploited to drive electric quadrupole transitions in nearby quantum emitters. In this paper, we report on the observation of the 5S 1/2 → 4D 3/2 electric quadrupole transition at 516.6 nm (in vacuum) in laser-cooled 87 Rb atoms using only a few μ W of laser power propagating through an optical nanofibre embedded in the atom cloud. This work extends the range of applications for optical nanofibres in atomic physics to include more fundamental tests such as high-precision measurements of parity non-conservation.

We report on an experimental test of the spin selection rule for two-photon transitions in atoms. In particular, we demonstrate that the $5S_{1/2}\to 6S_{1/2}$ transition rate in a rubidium gas follows a quadratic dependency on the helicity parameter linked to the polarization of the excitation light. For excitation via a single Gaussian beam or two counterpropagating beams in a hot vapor cell, the transition rate scales as the squared degree of linear polarization. The rate reaches zero when the light is circularly polarized. In contrast, when the excitation is realized via an evanescent field near an optical nanofiber, the two-photon transition cannot be completely extinguished (theoretically, not lower than 13\% of the maximum rate, under our experimental conditions) by only varying the polarization of the fiber-guided light. Our findings lead to a deeper understanding of the physics of multiphoton processes in atoms in strongly nonparaxial light.

Optical nanofibers (ONF) have been proved useful tools to probe cold atomic systems. Due to the intense evanescent field at their waist, ONFs have been used to probe or even trap atoms. However, very little experimental work has been done on exploiting the higher order modes (HOM) of such devices. The HOMs feature inhomogeneous polarization distributions around the ONF’s waist and can lead to the guiding of light carrying orbital angular momentum (OAM), via selective excitation of modes. In this work, we have experimentally studied the interaction between an ensemble of cold rubidium atoms and the HOMs of an ONF. The ONF, tailored to allow propagation of the first 6 guided modes at 780 nm, is embedded in a cold atomic ensemble and its modes are selectively excited by coupling vector beams from free-space. Using modal decomposition at the output of the ONF, we can calculate the transfer matrix of the system. This information, when combined with the amplitude extinction resulting from the scattering of the guided light by atoms surrounding the waist, allows us to non-destructively infer the modal excitation at the waist of the ONF. We further investigate the effect of temperature-induced strain on the modal decomposition at the waist and fiber output pigtail. Our results allow us to encode more than one quantum of information on the total angular momentum of a single guided photon. The inhomogeneous polarization distributions featured by the HOMs also offer a new tool to study chiral quantum systems.

We experimentally demonstrate a one-color two-photon transition from the 5S1/2 ground state to the 6S1/2 excited state in rubidium (Rb) vapor using a continuous wave laser at 993 nm. The Rb vapor contains both isotopes (85Rb and 87Rb) in their natural abundances. The electric dipole-allowed transitions are characterized by varying the power and polarization of the excitation laser. Since the optical setup is relatively simple, and the energies of the allowed levels are impervious to stray magnetic fields, this is an attractive choice for a frequency reference at 993 nm, with possible applications in precision measurements and quantum information processing.

An optical nanofiber is overlapped with a magneto-optical trap in order to investigate formation and characteristics of Rydberg atoms near a dielectric surface. Formation of Rydberg atoms was confirmed and atom loss rates were determined.