Summary form only given. Reversible light-matter interfaces are crucial elements in quantum optics and quantum information networks. In particular, the coupling of one-dimensional bosonic nanoscale waveguides and cold atoms appears as a promising pathway to build strong light-matter interaction thanks to the tight transverse confinement of light.Recently, our group has developed an interface where light, tightly guided by a subwavelength-diameter optical fiber (nanofiber), strongly interacts with atoms near its vicinity. In this case, a single atom close to the surface can absorb a non-negligible fraction of the guided light, as the effective area of the mode is comparable with the atomic cross-section. Moreover, using this configuration, it is possible to generate an in-fiber dipole trap for atoms in the vicinity of the waveguide. Using this all-fibered interface we have recently demonstrated the realization of an optical memory at the single photon level [1]. Here, we will describe the most recent result using this new interface: the observation of a large Bragg reflection off a 1D optical lattice [2]. The ability to control photon transport in 1D waveguides coupled to spin systems would allow for novel quantum network capabilities and many-body effects emerging from long-range interactions.
Summary form only given. Reversible light-matter interfaces are crucial elements in quantum optics and quantum information networks. In particular, the coupling of one-dimensional bosonic nanoscale waveguides and cold atoms appears as a promising pathway to build strong light-matter interaction thanks to the tight transverse confinement of light.Recently, our group has developed an interface where light, tightly guided by a subwavelength-diameter optical fiber (nanofiber), strongly interacts with atoms near its vicinity. In this case, a single atom close to the surface can absorb a non-negligible fraction of the guided light, as the effective area of the mode is comparable with the atomic cross-section. Moreover, using this configuration, it is possible to generate an in-fiber dipole trap for atoms in the vicinity of the waveguide. Using this all-fibered interface we have recently demonstrated the realization of an optical memory at the single photon level [1]. Here, we will describe the most recent result using this new interface: the observation of a large Bragg reflection off a 1D optical lattice [2]. The ability to control photon transport in 1D waveguides coupled to spin systems would allow for novel quantum network capabilities and many-body effects emerging from long-range interactions.
We report experimental observations of a large Bragg reflection from arrays of cold atoms trapped near a one-dimensional nanoscale waveguide. By using an optical lattice in the evanescent field surrounding a nanofiber with a period nearly commensurate with the resonant wavelength, we observe a reflectance of up to 75% for the guided mode. Each atom behaves as a partially reflecting mirror and an ordered chain of about 2000 atoms is sufficient to realize an efficient Bragg mirror. Measurements of the reflection spectra as a function of the lattice period and the probe polarization are reported. The latter shows the effect of the chiral character of nanoscale waveguides on this reflection. The ability to control photon transport in 1D waveguides coupled to spin systems would enable novel quantum network capabilities and the study of many-body effects emerging from long-range interactions.
Summary form only given. Developing light-matter interfaces is a crucial capability with unique applications to quantum optics and quantum information networks [1]. In this context, our group focuses on the study of interactions between photons guided by nanoscale waveguides and arrays of trapped atoms. Nanoscale waveguides offer a compelling platform because of the tight transverse confinement of the propagating light, the strong photon-atom coupling in single pass, and the potential long-range atom-atom interaction mediated by the guided photons [2]. Our platform, based on an optical nanofiber, already allowed the demonstration of an all-fibered optical memory with a storage and retrieval efficiency ri = 10% and a high SNR at the single photon level [3]. Then, by using an optical lattice in the evanescent field surrounding the nanofiber with a period close to commensurate with the resonant wavelength, we demonstrated large Bragg reflection by the 1D array of trapped atoms [4].
Abstract Recent advances in the coherent control of single quanta of light, photons , is a topic of prime interest, and is discussed under the banner of quantum photonics . In the last decade, the subwavelength diameter waist of a tapered optical fiber, referred to as an optical nanofiber , has opened promising new avenues in the field of quantum optics, paving the way toward a versatile platform for quantum photonics applications. The key feature of the technique is that the optical field can be tightly confined in the transverse direction while propagating over long distances as a guided mode and enabling strong interaction with the surrounding medium in the evanescent region. This feature has led to surprising possibilities to manipulate single atoms and fiber-guided photons, e.g. the efficient channeling of emission from single atoms and solid-state quantum emitters into the fiber-guided modes, high optical depth with a few atoms around the nanofiber, trapping atoms around a nanofiber, and atomic memories for fiber-guided photons. Furthermore, implementing a moderate longitudinal confinement in nanofiber cavities has enabled the strong coupling regime of cavity quantum electrodynamics to be reached, and the long-range dipole–dipole interaction between quantum emitters mediated by the nanofiber offers a platform for quantum nonlinear optics with an ensemble of atoms. In addition, the presence of a longitudinal component of the guided field has led to unique capabilities for chiral light–matter interactions on nanofibers. In this article, we review the key developments of the nanofiber technology toward a vision for quantum photonics on an all-fiber interface.
Developing light-matter interfaces is a crucial capability with unique applications to quantum optics and quantum information networks. In this context, our group focuses on the development of quantum memories in cold, neutral atom clouds, using both electromagnetically-induced transparency (EIT) and DLCZ as interacting schemes [1]. We recently reported for instance the quantum storage of qubits encoded in the orbital angular momentum degree of freedom [2]. Here, we demonstrate [3] for the first time EIT and optical storage at the single-photon level for the light tightly guided by a subwavelength-diameter optical fiber, aka nanofiber. In a nanofiber, the guided photons are highly confined and the majority of the light power travels in the evanescent field outside the glass. This new setting is a promising alternative to free-space focusing, which limits the interaction one can obtain, and provides a novel platform for developing all-fibered quantum networks.
We built a new experiment using cold atoms interacting with the light guided by an optical nanofiber. We first developed a nanofiber manufacturing bench. By heating and stretching a commercial optical fiber, a silica cylinder of 400 nm diameter is obtained. The light guided in these nanofibers is strongly focused over the whole length and exhibits strong evanescent fields. We then prepared a vacuum chamber and the laser system necessary for the manipulation of cold atoms. After inserting a nanofiber amid a cloud of cold atoms, we observed the phenomenon of slow light under the conditions of electromagnetically induced transparency: the light guided by the fiber is slowed down to a speed 3000 times smaller than its usual speed. We also stored the light guided by an optical fiber. After several microseconds, the information stored as a collective atomic excitation could be retrieved in the fiber. We have shown that this optical memory works for light pulses containing less than one photon on average. This system may therefore be used as a quantum memory, an essential tool for future quantum communication networks. Finally, we trapped atoms in an array in the vicinity of the nanofiber thanks to the light guided by the latter. Compared to our first set of experiments, the resulting cloud has a longer lifetime (25 ms) and interacts more strongly with the guided light (OD ~ 100). This new system should allow to efficiently implement other quantum optics protocols, such as the generation of single photons, or the entanglement of two remote atomic ensembles.
Techniques to controllably interface atoms with quantum optical fields form the basis for many applications in quantum information science. For example, photons are convenient to relay information over large quantum networks, while atoms naturally are physical systems that can process and store this information. Thus far, the available techniques to efficiently couple single photons with atomic media fall into one of the following, mostly independent, categories: i) cavity quantum electrodynamics (QED), where atomic interactions with light are enhanced via a high-finesse cavity, ii) coherent coupling with atomic ensembles exhibiting large optical depths, and iii) the use of fields tightly focused to dimensions smaller than or approaching the scattering cross-section of a single atom. Although remarkable achievements have been made with all of these approaches, a robust, scalable technique remains elusive. Recently, several groups have successfully demonstrated that cold atoms can be trapped near and interfaced with nanophotonic systems, such as hollow-core photonic crystal fibers [1] and tapered nanofibers [2–4]. The traps are well-characterized [2, 3, 5], and the nearly diffraction-limited transverse confinement of optical fields enables ∼ 10% coupling efficiency of a single atom to the fiber [2, 3]. This has already led to remarkable observations of strong light-matter interactions using relatively few atoms and low powers [1]. It has also been proposed that such techniques can be extended to highly configurable photonic crystal waveguides [6]. Together, these efforts raise the intriguing possibility for future nanophotonic systems with tremendous figures of merit, wherein atom-light interactions can be tailored nearly at will. Here, we discuss recent efforts to develop novel techniques to realize strong, controllable atom-photon and photon-photon interactions, which take full advantage of the parameter space afforded by nanophotonic interfaces and are not based upon the extension of existing techniques. As a specific example, we discuss a protocol to achieve “all-atomic” cavity QED [7], as briefly described below. First, we show that although the single-atom coupling to guided modes of a nanophotonic waveguide might be relatively weak, there exist collective modes of a trapped atomic ensemble whose coupling to light is enhanced by the square root of the atom number, √ NA. While collective effects are generally well-known, special consequences emerge in the nanofiber system when the atoms are trapped in a lattice. In particular, collective effects cause such a lattice to act as a near-perfect mirror for an incident field close to resonance. In analogy to cavity QED, we then demonstrate that two sets of atomic mirrors can form an effective cavity, which can greatly enhance the coupling of a single, specially chosen “impurity” atom (or a few impurity atoms) positioned inside. We introduce a novel quantum spin model to describe the atom-light coupling, which allows one to exactly map the atom-nanofiber interface onto the simple and elegant Jaynes-Cummings model of cavity QED [8]. A unique feature of our atomic mirrors compared to conventional cavities is that they have long relaxation times and are highly dispersive. Remarkably, even with very low mirror finesse (F ∼ 10 2 ), this property allows one to attain the “strong coupling” regime of cavity QED, where vacuum Rabi oscillations [9–12] occur between an excited impurity atom and a single “photon” stored in the cavity (or more precisely, in the atomic mirrors). Furthermore, as quantum mechanical objects, these atom mirrors can be used to store quantum information and transfer this information into propagating waveguide modes. These various features can be combined to realize all of the building blocks for scalable quantum information processing.