Waveguide-coupled single collective excitation of atomic
Large Bragg reflection from one-dimensional chains of trapped atoms near a nanoscale waveguide (2016)
Phys. Rev. Lett. 117, 133603
Demonstration of a memory for tightly guided light in an optical nanofiber (2015)
Phys. Rev. Lett. 114, 180503
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Interfacing guided light with atoms enables long interaction length, large optical depth and non-linear interactions at low power level. Cold atoms are combined here with subwavelength nanofiber for the realization of integrated single-photon sources and quantum memories and the exploration of effects related to one-dimensional lattices.
Waveguide-coupled single collective excitation of atomic arrays
Considerable efforts have been recently devoted to combining ultracold atoms and nanophotonic devices to obtain not only better scalability and figures of merit than in free-space implementations, but also new paradigms for atom–photon interactions. Dielectric waveguides offer a promising platform for such integration because they enable tight transverse confinement of the propagating light, strong photon–atom coupling in single-pass configurations and potentially long-range atom–atom interactions mediated by the guided photons. However, the preparation of non-classical quantum states in such atom–waveguide interfaces has not yet been realized. Here, by using arrays of individual caesium atoms trapped along an optical nanofibre, we observed a single collective atomic excitationcoupled to a nanoscale waveguide. The stored collective entangled state can be efficiently read out with an external laser pulse, leading to on-demand emission of a single photon into the guided mode. We characterize the emitted single photon via the suppression of the two-photon component and confirm the single character of the atomic excitation, which can be retrieved with an efficiency of about 25%. Our results demonstrate a capability that is essential for the emerging field of waveguide quantum electrodynamics, with applications to quantum networking, quantum nonlinear optics and quantum many-body physics.
The paper: Nature (advance online publication) direct pdf available
Large bragg reflection from one-dimensional chains of trapped atoms
In this work, we reported experimental observations of 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 close to commensurate with the resonant wavelength, we observed a reflectance 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 allow for novel quantum network capabilities and many-body effects emerging from long-range interactions.
The paper: Phys. Rev. Lett. 117, 133603 (2016) arXiv version
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DEMONSTRATION OF A MEMORY FOR TIGHTLY GUIDED LIGHT IN AN OPTICAL NANOFIBER
In this study, we reported 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, we observed electromagnetically induced transparency and light pulses at the single-photon level were stored in and retrieved from the atomic medium with an overall efficiency of 10 %. Collapses and revivals were additionally controlled by an applied magnetic field. We also measured the decay of efficiency with storage time and investigated the concurrent decoherence mechanisms in this system. These results based on subdiffraction-limited optical mode interacting with atoms via the strong evanescent field demonstrate an alternative to free-space focusing and a novel capability for information storage in an all-fibered quantum network.
The paper: Physical Review Letters 114, 180503 (2015) arXiv version
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Fiber pulling bench
We built a fabrication bench for elongated nanofiber : a standard optical fiber is softened by heating and pulled until its diameter has reached a target value, around half the guided light wavelength. We obtain nanofiber coupled via tapered regions on both sides to the standard fiber. In order to preserve a high transmission, close to unity, and to keep control on the fiber guiding properties, the taper is made with a carefully designed shape. This adiabatic shape is obtained using the flame-brushing technique : the back and forth movement of a clean hydrogen/oxygen flame allows the dynamically change of the effective heating width. Therefore any desired shape can be produced. Real time monitoring is available via imaging, but also via the rich propagation properties of a laser beam guided by the fiber being pulled. The produced nanofiber are further characterized with the SEM facility available in UPMC. In addition to our cold atoms experiment, the fabrication beanch is used by different groups at LKB and UPMC. Our nanofibers are used for instance for collecting light from nanoscale single-photon emitters and they also helped recently to understand the properties of spider silk.