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We demonstrate optical nonlinearities due to the interaction of weak optical fields with the collective motion of a strongly dispersive ultracold gas. The combination of a recoil-induced resonance (RIR) in the high gain regime and optical waveguiding within the dispersive medium enables us to achieve a collective atomic cooperativity of $275 \pm 50$ even in the absence of a cavity. As a result, we observe optical bistability at input powers as low as 20 pW. The present scheme allows for dynamic optical control of the dispersive properties of the ultracold gas using very weak pulses of light. The experimental observations are in good agreement with a theoretical model.

We demonstrate perfect coherence preservation in an atom interferometer perturbed by kicks from off-resonant standing wave pulses. Under most conditions, the decoherence induced by the pulses reduces the signal; however, the coherence is perfectly preserved when the kicking period is equal to the rational fraction of the inverse atomic recoil frequency, independent of the number or the randomness of the strength of the applied kicks. The width narrowing of coherence revival as a function of increasing kick number and strength provides a new accurate measurement of the recoil frequency.

It had been proposed that overstretching double stranded DNA from the 5-5 ends will produce a new fiber form of dsDNA that is narrower than the S form that has been suggested to result when the dsDNA is overstretched from the 3-3 ends. We present the first comparison of the structures that result when dsDNA is overstretched from the 5-5, 3-3, and 3-5 ends and show that the stability of the overstretched form depends on the ends to which the force is applied. The stability also depends strongly on the ionic environment as well as the presence of reagents that bind to ssDNA.

We measured the relative phase of two Bose-Einstein condensates confined in an radio frequency induced double well potential on an atom chip. We observed phase coherence between the separated condensates for times up to 200 ms after splitting, a factor of 10 beyond the phase diffusion limit expected for a coherent state in our experimental conditions (20 ms). The enhanced coherence time is attributed to number squeezing of the initial state by a factor of 10. In addition, we demonstrated a rotationally sensitive (Sagnac) geometry for a guided atom interferometer by propagating the split condensates., Comment: 5 pages, 5 figures

We have used a microfabricated atom chip to split a single Bose-Einstein condensate of sodium atoms into two spatially separated condensates. Dynamical splitting was achieved by deforming the trap along the tightly confining direction into a purely magnetic double-well potential. We observed the matter wave interference pattern formed upon releasing the condensates from the microtraps. The intrinsic features of the quartic potential at the merge point, such as zero trap frequency and extremely high field-sensitivity, caused random variations of the relative phase between the two split condensates. Moreover, the perturbation from the abrupt change of the trapping potential during the splitting was observed to induce vortices., Comment: 4 pages, 5 figures

Doubly quantized vortices were topologically imprinted in $|F=1>$ $^{23}$Na condensates, and their time evolution was observed using a tomographic imaging technique. The decay into two singly quantized vortices was characterized and attributed to dynamical instability. The time scale of the splitting process was found to be longer at higher atom density., Comment: 5 pages, 4 figures

Under constant applied force, the separation of double-stranded DNA into two single strands is known to proceed through a series of pauses and jumps. Given experimental traces of constant-force unzipping, we present a method whereby the locations of pause points can be extracted in the form of a pause point spectrum. A simple theoretical model of DNA constant-force unzipping is demonstrated to produce good agreement with the experimental pause point spectrum of lambda phage DNA. The locations of peaks in the experimental and theoretical pause point spectra are found to be nearly coincident below 6000 bp. The model only requires the sequence, temperature and a set of empirical base pair binding and stacking energy parameters, and the good agreement with experiment suggests that pause points are primarily determined by the DNA sequence. The model is also used to predict pause point spectra for the BacterioPhage PhiX174 genome. The algorithm for extracting the pause point spectrum might also be useful for studying related systems which exhibit pausing behavior such as molecular motors., Comment: 15 pages, 12 figures

We separate double stranded lambda phage DNA by applying a fixed force at a constant temperature ranging from 15C to 50C, and measure the minimum force required to separate the two strands, providing the first experimental determination of the phase boundary between single stranded DNA and double stranded DNA in the temperature- force plane. The measurements also offer information on the free energy of dsDNA at temperatures where dsDNA does not thermally denature in the absence of force. While parts of the phase diagram can be explained using existing models and free energy parameters, others deviate significantly. Possible reasons for the deviations between theory and experiment are considered., Comment: 17 pages, 2 figures

We report a compact (<20cm3), robust source for producing a bright flux of cold atoms, which can be loaded efficiently into a magnetic guide. A continuous flux of up to 8 x 109 87Rb atoms/s have been produced from this 2D+ vapor cell MOT. The flux had a divergence of 12.5 mrad and velocity could be controlled in the range 2-15 m/s. This flux was coupled continuously into a magnetic guide with high efficiency., Comment: 20 pages, 4 figures

We demonstrate the use of frequency-encoded light masks in neutral atom lithography. We demonstrate that multiple features can be patterned across a monotonic potential gradient. Features as narrow as 0.9 microns are fabricated on silicon substrates with a metastable argon beam. Internal state manipulation with such a mask enables continuously adjustable feature positions and feature densities not limited by the optical wavelength, unlike previous light masks., Comment: 4 pages, 4 figures

Magneto-optic and magnetostatic trapping is realized near a surface using current carrying coils wrapped around magnetizable cores. A cloud of 10^7 Cesium atoms is created with currents less than 50 mA. Ramping up the current while maintaining optical dissipation leads to tightly confined atom clouds with an aspect ratio of 1:1000. We study the 3D character of the magnetic potential and characterize atom number and density as a function of the applied current. The field gradient in the transverse dimension has been varied from < 10 G/cm to > 1 kG/cm. By loading and cooling atoms in-situ, we have eliminated the problem of coupling from a MOT into a smaller phase space., Comment: 4 pages, 4 figures

We show that the conductance of neutral atoms through a tightly confining waveguide constriction is quantized in units of lambda_dB^2/pi, where lambda_dB is the de Broglie wavelength of the incident atoms. Such a constriction forms the atom analogue of an electron quantum point contact and is an example of quantum transport of neutral atoms in an aperiodic system. We present a practical constriction geometry that can be realized using a microfabricated magnetic waveguide, and discuss how a pair of such constrictions can be used to study the quantum statistics of weakly interacting gases in small traps., Comment: 5 pages with 3 figures. To appear in Phys. Rev. Lett

Cryogenically cooled microelectromagnet mirrors were used to reflect a cloud of free-falling laser-cooled 85Rb atoms at normal incidence. The mirrors consisted of microfabricated current-carrying Au wires in a periodic serpentine pattern on a sapphire substrate. The fluorescence from the atomic cloud was imaged after it had bounced off a mirror. The transverse width of the cloud reached a local minimum at an optimal current corresponding to minimum mirror roughness. A distinct increase in roughness was found for mirror configurations with even versus odd number of lines. These observations confirm theoretical predictions., Comment: Physical Review A, in print; 11 pages, 4 figures

We demonstrate the guiding of neutral atoms by the magnetic fields due to microfabricated current-carrying wires on a chip. Atoms are guided along a magnetic field minimum parallel to and above the current-carrying wires. Two waveguide configurations are demonstrated: one using two wires with an external magnetic field, and a second using four wires without an external field. These waveguide geometries can be extended to integrated atom optics circuits, including beamsplitters., Comment: 11 pages, 4 figures

We propose a dipole-force linear waveguide which confines neutral atoms up to lambda/2 above a microfabricated single-mode dielectric optical guide. The optical guide carries far blue-detuned light in the horizontally-polarized TE mode and far red-detuned light in the vertically-polarized TM mode, with both modes close to optical cut-off. A trapping minimum in the transverse plane is formed above the optical guide due to the differing evanescent decay lengths of the two modes. This design allows manufacture of mechanically stable atom-optical elements on a substrate. We calculate the full vector bound modes for an arbitrary guide shape using two-dimensional non-uniform finite elements in the frequency-domain, allowing us to optimize atom waveguide properties. We find that a rectangular optical guide of 0.8um by 0.2um carrying 6mW of total laser power (detuning +-15nm about the D2 line) gives a trap depth of 200uK for cesium atoms (m_F = 0), transverse oscillation frequencies of f_x = 40kHz and f_y = 160kHz, collection area ~ 1um^2 and coherence time of 9ms. We discuss the effects of non-zero m_F, surface interactions, heating rate, the substrate refractive index, and the limits on waveguide bending radius., Comment: 12 pages, 4 figures, revtex, submitted to Phys. Rev. A Replaced: final version accepted by PRA v.61 Feb 2000. (2 paragraphs added)

We propose a simple method for the deterministic generation of an arbitrary continuous quantum state of the center-of-mass of an atom. The method's spatial resolution gradually increases with the interaction time with no apparent fundamental limitations. Such de-Broglie Wave-Front Engineering of the atomic density can find applications in Atom Lithography, and we discuss possible implementations of our scheme in atomic beam experiments., Comment: The figures' quality was improved, the text remains intact. 5 pages, 3 figures; submitted to PRL