Subwavelength features in conjunction with light‐guiding structures have gained significant interest in recent decades due to their wide range of applications to particle and atom trapping. Lately, the focus of particle trapping has shifted from the microscale to the nanoscale. This few orders of magnitude change is driven, in part, by the needs of life scientists who wish to better manipulate smaller biological samples. Devices with subwavelength features are excellent platforms for shaping local electric fields for this purpose. A major factor that inhibits the manipulation of submicrometer particles is the diffraction‐limited spot size of free‐space laser beams. As a result, technologies that can circumvent this limit are highly desirable. This review covers some of the more significant advances in the field, from the earliest attempts at trapping using focused Gaussian beams, to more sophisticated hybrid plasmonic/metamaterial structures. In particular, examples of emerging optical trapping configurations are presented.

We propose an optical dipole trap for cold, neutral atoms based on the electric field produced from the evanescent fields in a hollow, rectangular slot cut through an optical nanofibre. In particular, we discuss the trap performance in relation to laser-cooled rubidium atoms and show that a far off-resonance, bluedetuned field combined with the attractive surface-atom interaction potential from the dielectric material forms a stable trapping configuration. With the addition of a red-detuned field, we demonstrate how three dimensional confinement of the atoms at a distance of 140-200 nm from the fibre surface within the slot can be accomplished. This scheme facilitates optical coupling between the atoms and the nanofibre that could be exploited for quantum communication schemes using ensembles of laser-cooled atoms. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. New J. Phys. 16 (2014) 053052 M Daly et al New J. Phys. 16 (2014) 053052 M Daly et al 3 New J. Phys. 16 (2014) 053052 M Daly et al 4 New J. Phys. 16 (2014) 053052 M Daly et al New J. Phys. 16 (2014) 053052 M Daly et al 6 Figure 4. Graph of the regions of single-mode and multimode operation for 720 nm wavelength. New J. Phys. 16 (2014) 053052 M Daly et al 9

We present a method for measuring the average temperature of a cloud of cold 85Rb atoms in a magneto-optical trap using an optical nanofibre. A periodic spatial variation is applied to the magnetic fields generated by the trapping coils and this causes the trap centre to oscillate, which, in turn, causes the cloud of cold atoms to oscillate. The optical nanofibre is used to collect the fluorescence emitted by the cold atoms, and the frequency response between the motion of the centre of the oscillating trap and the cloud of atoms is determined. This allows us to make measurements of cloud temperature both above and below the Doppler limit, thereby paving the way for nanofibres to be integrated with ultracold atoms for hybrid quantum devices.

While conventional optical trapping techniques can trap objects with submicron dimensions, the underlying limits imposed by the diffraction of light generally restrict their use to larger or higher refractive index particles. As the index and diameter decrease, the trapping difficulty rapidly increases; hence, the power requirements for stable trapping become so large as to quickly denature the trapped objects in such diffraction-limited systems. Here, we present an evanescent field-based device capable of confining low index nanoscale particles using modest optical powers as low as 1.2 mW, with additional applications in the field of cold atom trapping. Our experiment uses a nanostructured optical micro-nanofiber to trap 200 nm, low index contrast, fluorescent particles within the structured region, thereby overcoming diffraction limitations. We analyze the trapping potential of this device both experimentally and theoretically, and show how strong optical traps are achieved with low input powers.

Articles you may be interested inBroadband transient absorption spectroscopy with 1-and 2-photon excitations: Relaxation paths and cross sections of a triphenylamine dye in solution ( ns 1/2 + np 1/2 )0 g − Rb 2 and Cs 2 photo-associative spectroscopy of weakly bound levels: Lu-Fano analysis coupled to an improved LeRoy-Bernstein formula.Optical transfer cavity stabilization using current-modulated injection-locked diode lasers Rev. Sci. Instrum. 77, 093105 (2006); 10.1063/1.2337094 Collimated, single-pass atom source from a pulsed alkali metal dispenser for laser-cooling experiments Rev. Sci. Instrum. 76, 023106 (2005);Abstract. The characteristics of a cold cloud of 85 Rb can be non-destructively examined using an optical nanofiber. The nanofiber is a submicron-diameter cylindrical waveguide fabricated from commercially-available optical fiber using a heat-and-pull rig. The nanofiber can be used as a 'dark' or 'bright' probe depending on whether laser light is coupled into the nanofiber. We demonstrate the use of an optical nanofiber as an absorption spectroscopy tool for cold atoms. A frequency-scanned probe beam is launched through the nanofiber and the resonant light is absorbed at the waist of the nanofiber by nearby cold 85 Rb atoms. We present recent singlephoton absorption results and comment on the role of surface interactions. Future work on 2photon absorption using excited state electronic transitions in 85 Rb is discussed.