The integration of nanophotonics and atomic physics has been a long-sought goal that would open new frontiers for optical physics, including novel quantum transport and many-body phenomena with photon-mediated atomic interactions. Reaching this goal requires surmounting diverse challenges in nanofabrication and atomic manipulation. Here we report the development of a novel integrated optical circuit with a photonic crystal capable of both localizing and interfacing atoms with guided photons. Optical bands of a photonic crystal waveguide are aligned with selected atomic transitions. From reflection spectra measured with average atom number N ¼ 1:1 AE 0:4, we infer that atoms are localized within the waveguide by optical dipole forces. The fraction of single-atom radiative decay into the waveguide is G 1D /G 0 C(0.32 ± 0.08), where G 1D is the rate of emission into the guided mode and G 0 is the decay rate into all other channels. G 1D /G 0 is unprecedented in all current atom-photon interfaces.

We report observations of superradiance for atoms trapped in the near field of a photonic crystal waveguide (PCW). By fabricating the PCW with a band edge near the D 1 transition of atomic cesium, strong interaction is achieved between trapped atoms and guided-mode photons. Following short-pulse excitation, we record the decay of guided-mode emission and find a superradiant emission rate scaling as Γ SR ∝NΓ 1D for average atom number 0.19 ≲N ≲ 2.6 atoms, where Γ 1D =Γ 0 ¼ 1.0 AE 0.1 is the peak singleatom radiative decay rate into the PCW guided mode, and Γ 0 is the radiative decay rate into all the other channels. These advances provide new tools for investigations of photon-mediated atom-atom interactions in the many-body regime. DOI: 10.1103/PhysRevLett.115.063601 PACS numbers: 42.50.Ct, 37.10.Gh, 42.70.Qs Interfacing light with atoms localized near nanophotonic structures has attracted increasing attention in recent years. Exemplary experimental platforms include nanofibers [1][2][3], photonic crystal cavities [4], and waveguides [5,6]. Owing to their small optical loss and tight field confinement, these nanoscale dielectric devices are capable of mediating long-range atom-atom interactions using photons propagating in their guided modes. This new paradigm for strong interaction of atoms and optical photons offers new tools for scalable quantum networks [7], quantum phases of light and matter [8,9], and quantum metrology [10].In particular, powerful capabilities for dispersion and modal engineering in photonic crystal waveguides (PCWs) provide opportunities beyond conventional settings in atomic, molecular and optical physics within the new field of waveguide QED [2,3,6,[11][12][13]. For example, the edge of a photonic band gap aligned near an atomic transition strongly enhances single-atom emission into the one-dimensional (1D) PCW due to a "slow-light" effect [14][15][16]. Because the electric field of a guided mode near the band edge approaches a standing wave, optical excitations can be induced in an array of trapped atoms with little propagation phase error, resulting in phase-matched superradiant emission [17,18] into both forward and backward waveguide modes of the PCW. Superradiance has important applications for realizing quantum memories [19][20][21][22][23], single-photon sources [24,25], laser cooling by way of cooperative emission [26,27], and narrow linewidth lasers [28]. Related cooperative effects are predicted in nanophotonic waveguides absent an external cavity [29], including atomic Bragg mirrors [30] and selforganizing crystals of atoms and light [31][32][33].Complimentary to superradiant emission is the collective Lamb shift induced by proximal atoms virtually exchanging off-resonant photons [34][35][36][37]. With the atomic transition frequency placed in a photonic band gap of a PCW, real photon emission is largely suppressed. Coherent atomatom interactions then emerge as a dominant effect for QED with atoms in band-gap materials [38][39][40][41][42][43]. Both the strength and lengt...

Tailoring the interactions between quantum emitters and single photons constitutes one of the cornerstones of quantum optics. Coupling a quantum emitter to the band edge of a photonic crystal waveguide (PCW) provides a unique platform for tuning these interactions. In particular, the cross-over from propagating fields E(x) ∝ e ±ikx x outside the bandgap to localized fields E(x) ∝ e −κx jxj within the bandgap should be accompanied by a transition from largely dissipative atom-atom interactions to a regime where dispersive atom-atom interactions are dominant. Here, we experimentally observe this transition by shifting the band edge frequency of the PCW relative to the D 1 line of atomic cesium for N = 3.0 ± 0.5 atoms trapped along the PCW. Our results are the initial demonstration of this paradigm for coherent atomatom interactions with low dissipation into the guided mode.quantum optics | nanophotonics | atomic physics R ecent years have witnessed a spark of interest in combining atoms and other quantum emitters with photonic nanostructures (1). Many efforts have focused on enhancing emission into preferred electromagnetic modes relative to vacuum emission, thereby establishing efficient quantum matter-light interfaces and enabling diverse protocols in quantum information processing (2). Photonic structures developed for this purpose include high-quality cavities (3-7), dielectric fibers (8-13), metallic waveguides (14-16), and superconducting circuits (17-19). Photonic crystal waveguides (PCWs) are of particular interest, because the periodicity of the dielectric structure drastically modifies the field propagation, yielding a set of Bloch bands for the guided modes (GMs) (20). For example, recent experiments have shown superradiant atomic emission because of a reduction in group velocity for an atomic frequency near a band edge of a PCW (21).A quite different paradigm for atom-light interactions in photonic crystals was proposed in the works in refs. 22-25 but has yet to be experimentally explored. In particular, when an atomic transition frequency is situated within a bandgap of a PCW, an atom can no longer emit propagating waves into GMs of the structure. However, an evanescent wave surrounding the atoms can still form, resulting in the formation of atom-photon-bound states (26,27). This phenomenon has attracted new interest recently as a means to realize dispersive interactions between atoms without dissipative decay into GMs. The spatial range of atomatom interactions is tunable for 1D and 2D PCWs and set by the size of the photonic component of the bound state (28, 29). Manybody physics with large spin exchange energies and low dissipation can thereby be realized in a generalization of cavity quantum electrodynamics (CQED) arrays (30,31). Fueled by such perspectives, there have been recent experimental observations with atoms (21, 32, 33) and quantum dots (34, 35) interacting through the GMs of PCWs, albeit in frequency regions outside the bandgap, where GMs are propagating fields.In this manuscript, we re...

Based on a formalism that describes atom-light interactions in terms of the classical electromagnetic Green's function, we study the optical response of atoms and other quantum emitters coupled to one-dimensional photonic structures, such as cavities, waveguides, and photonic crystals. We demonstrate a clear mapping between the transmission spectra and the local Green's function, identifying signatures of dispersive and dissipative interactions between atoms. We also demonstrate the applicability of our analysis to problems involving three-level atoms, such as electromagnetically induced transparency. Finally we examine recent experiments, and anticipate future observations of atom-atom interactions in photonic bandgaps.

Chemical reactions typically proceed via stochastic encounters between reactants. Going beyond this paradigm, we combined exactly two atoms in a single, controlled reaction. The experimental apparatus traps two individual laser-cooled atoms [one sodium (Na) and one cesium (Cs)] in separate optical tweezers and then merges them into one optical dipole trap. Subsequently, photoassociation forms an excited-state NaCs molecule. The discovery of previously unseen resonances near the molecular dissociation threshold and measurement of collision rates are enabled by the tightly trapped ultracold sample of atoms. As laser-cooling and trapping capabilities are extended to more elements, the technique will enable the study of more diverse, and eventually more complex, molecules in an isolated environment, as well as synthesis of designer molecules for qubits.

We present a comprehensive study of dispersion-engineered nanowire photonic crystal waveguides suitable for experiments in quantum optics and atomic physics with optically trapped atoms. Detailed design methodology and specifications are provided, as are the processing steps used to create silicon nitride waveguides of low optical loss in the near-IR. Measurements of the waveguide optical properties and power-handling capability are also presented.

We demonstrate full quantum state control of two species of single atoms using optical tweezers and assemble the atoms into a molecule. Our demonstration includes 3D ground-state cooling of a single atom (Cs) in an optical tweezer, transport by several microns with minimal heating, and merging with a single Na atom. Subsequently, both atoms occupy the simultaneous motional ground state with 61(4)% probability. This realizes a sample of exactly two co-trapped atoms near the phase-space-density limit of one, and allows for efficient stimulated-Raman transfer of a pair of atoms into a molecular bound state of the triplet electronic ground potential a 3 Σ + . The results are key steps toward coherent creation of single ultracold molecules, for future exploration of quantum simulation and quantum information processing.

The quality factor of a mechanical resonator is an important figure of merit for various sensing applications and for observing quantum behavior. Here, we demonstrate a technique to push the quality factor of a micromechanical resonator beyond conventional material and fabrication limits by using an optical field to stiffen or trap a particular motional mode. Optical forces increase the oscillation frequency by storing most of the mechanical energy in a nearly lossless optical potential, thereby strongly diluting the effect of material dissipation. By placing a 130 nm thick SiO 2 pendulum in an optical standing wave, we achieve an increase in the pendulum center-of-mass frequency from 6.2 to 145 kHz. The corresponding quality factor increases 50-fold from its intrinsic value to a final value of Q ¼ 5:8ð1:1Þ Â 10 5 , representing more than an order of magnitude improvement over the conventional limits of SiO 2 for this geometry. Our technique may enable new opportunities for mechanical sensing and facilitate observations of quantum behavior in this class of mechanical systems. DOI: 10.1103/PhysRevLett.108.214302 PACS numbers: 45.80.+r, 03.67.-a, 42.50.Wk, 62.25.-g Mechanical resonators are widely used as exquisite sensors of weak perturbations such as small forces [1,2], displacements [3,4], and changes in mass [5,6]. In fact, a number of systems have advanced to the point that it is possible to detect quantum effects in their motion [4,[7][8][9], raising the exciting possibility that such systems might eventually lead to applications in quantum information processing [10][11][12] and the observation of quantum effects at macroscopic scales [13,14].The performance of a mechanical resonator depends critically on its quality factor, which characterizes both the maximum response of an oscillator to a disturbance at its resonance frequency (signal) and the coupling rate to its surrounding dissipative environment (noise). Improving quality factors beyond state-of-the-art parameters is a challenging task since a number of systems are now limited by fundamental dissipation mechanisms, e.g., thermoelastic damping [15] and internal friction [16].In this Letter, we experimentally demonstrate a technique that enables the quality factor of a mechanical system to be enhanced beyond conventional material limits. Our technique involves optically trapping a thin, dielectric membrane whose geometry is designed so that the natural material forces are extremely weak [17]. In this limit, almost all mechanical energy is stored in an ultralow-loss potential provided by strong optical restoring forces, which dilute the effects of internal material dissipation [17,18]. The trapped oscillator is analogous to a mechanical oscillator with a spring that is stiffened by increased mechanical tensile stress [19][20][21] in that both the oscillator frequency and the Q increase. Our general scheme is implemented for a particular example of an SiO 2 dielectric disk supported by a single thin tether, trapped in an optical standing wave.We obse...