Super-radiance reveals infinite-range dipole interactions through a nanofiber.

Atoms interact with each other through the electromagnetic field, creating collective states that can radiate faster or slower than a single atom, i.e., super- and sub-radiance. When the field is confined to one dimension it enables infinite-range atom-atom interactions. Here we present the first report of infinite-range interactions between macroscopically separated atomic dipoles mediated by an optical waveguide. We use cold 87Rb atoms in the vicinity of a single-mode optical nanofiber (ONF) that coherently exchange evanescently coupled photons through the ONF mode. In particular, we observe super-radiance of a few atoms separated by hundreds of resonant wavelengths. The same platform allows us to measure sub-radiance, a rarely observed effect, presenting a unique tool for quantum optics. This result constitutes a proof of principle for collective behavior of macroscopically delocalized atomic states, a crucial element for new proposals in quantum information and many-body physics.

A low-loss photonic silica nanofiber for higher-order modes.

Optical nanofibers confine light to subwavelength scales, and are of interest for the design, integration, and interconnection of nanophotonic devices. Here we demonstrate high transmission (> 97%) of the first family of excited modes through a 350 nm radius fiber, by appropriate choice of the fiber and precise control of the taper geometry. We can design the nanofibers so that these modes propagate with most of their energy outside the waist region. We also present an optical setup for selectively launching these modes with less than 1% fundamental mode contamination. Our experimental results are in good agreement with simulations of the propagation. Multimode optical nanofibers expand the photonic toolbox, and may aid in the realization of a fully integrated nanoscale device for communication science, laser science or other sensing applications.

Observation of query pulse length dependent Ramsey interference in rubidium vapor using pulsed Raman excitation.

We report observation of query pulse length dependent Ramsey interference (QPLD-RI), using pulsed Raman excitation in rubidium vapor. This is observed when a long, attenuated query pulse is used during pulsed Raman excitation. We explain the physical mechanism behind the QPLD-RI using a Bloch vector model. We also use numerical solutions to time-dependent density matrix equations to simulate this interference effect, showing qualitative agreement with experimental results. Presence of such interference could create a potential source of error in a vapor cell Raman clock constructed using frequency-domain Ramsey interference (FDRI).

Cylindrical vector beams for rapid polarization-dependent measurements in atomic systems.

We demonstrate the use of cylindrical vector beams - beams with spatially varying polarization - for detecting and preparing the spin of a warm rubidium vapor in a spatially dependent manner. We show that a modified probe vector beam can serve as an atomic spin analyzer for an optically pumped medium, which spatially modulates absorption of the beam. We also demonstrate space-variant atomic spin by optical pumping with the vector beams. The beams are thus beneficial for making single-shot polarization-dependent measurements, as well as for providing a means of preparing samples with position-dependent spin.

Dynamic high-speed spatial manipulation of cold atoms using acousto-optic and spatial light modulation.

We demonstrate an experimental technique for high-resolution, high-speed spatial manipulation of atom clouds. By combining holographically engineered laser beams from a spatial light modulator with off-axis shear mode acousto-optic deflectors, we manipulate 1 x 3 arrays of cold atoms with individual site addressability. Additionally, we demonstrate smooth 2-dimensional motion of atomic ensembles, and the ability to guide multiple atomic ensembles independently.

Wideband frequency modulation of a mode-locked fiber laser.

We have demonstrated wideband frequency modulation of the frequency comb lines of a high-repetition-rate fiber laser. With a modulation frequency of only approximately 10 kHz, we have generated modulation indices in excess of 250. Although internally modulated, the laser remains stable with 2-kHz linewidths, and thus the 10-kHz modulation sidebands are still clearly resolved even after propagation over several hundred kilometers. This unique characteristic is used for simultaneous measurement of propagation distances to 1-m resolution and velocities of less than 3 mm/s over a distance of greater than 50 km.

Frequency comb linewidth of an actively mode-locked fiber laser.

We report what is to our knowledge the first measurement of the linewidth of the frequency comb lines of a mode-locked Er-doped fiber laser. By propagating the output pulses through fiber as long as 1000 km in a modified self-heterodyne arrangement, we have measured the effective linewidth of the comb lines to be less than 12 kHz on a 5-ms time scale; the width is due primarily to frequency jitter from environmental fluctuations. Deconvolution of the spectral line shapes by use of Voigt analysis yields an upper limit of the intrinsic Lorentzian width of 3 kHz.

Photodesorption of alkali anions from alkali-halide cluster anions.

Using photoelectron spectroscopy, we have observed alkali anion photodesorption from alkali-halide cluster anions that contain two weakly bound electrons. In the alkali iodides, we have found this type of desorption in almost every (MI)(n)M- cluster we have studied (M=Na, K, Cs; n<9), although it depends on the probe laser frequency and cluster temperature. Using pump-probe techniques, we have shown that the process occurs on a picosecond time scale by way of an electronic excitation of the cluster's spin-paired electrons.

Photoassociation of sodium in a Bose-Einstein condensate.

We form ultracold Na2 molecules by single-photon photoassociation of a Bose-Einstein condensate, measuring the photoassociation rate, linewidth, and light shift of the J = 1, v = 135 vibrational level of the A1 Sigma (+)(u) molecular state. The photoassociation rate constant increases linearly with intensity, even where it is predicted that many-body effects might limit the rate. Our observations are in good agreement with a two-body theory having no free parameters.

Analysis of nonadiabatically compressed pulses from dispersion-decreasing fiber.

Frequency-resolved optical gating is used to characterize ultrashort optical pulses that are compressed nonadiabatically in dispersion-decreasing fiber. The pulses undergo an interesting temporal pulse breakup following dispersion in both the normal and anomalous regimes, and compression ratios close to the adiabatic limit are obtained. All behaviors are in excellent agreement with numerical integration of the nonlinear Schrödinger equation.