Real-time control of the periodicity of a standing wave: an optical accordion.

We report an experimental method to create optical lattices with real-time control of their periodicity. We demonstrate a continuous change of the lattice periodicity from 0.96 microm to 11.2 microm in one second, while the center fringe only moves less than 2.7 microm during the whole process. This provides a powerful tool for controlling ultracold atoms in optical lattices, where small spacing is essential for quantum tunneling, and large spacing enables single-site manipulation and spatially resolved detection.

Spatial nonlocal pair correlations in a repulsive 1D Bose gas.

We analytically calculate the spatial nonlocal pair correlation function for an interacting uniform 1D Bose gas at finite temperature and propose an experimental method to measure nonlocal correlations. Our results span six different physical realms, including the weakly and strongly interacting regimes. We show explicitly that the characteristic correlation lengths are given by one of four length scales: the thermal de Broglie wavelength, the mean interparticle separation, the healing length, or the phase coherence length. In all regimes, we identify the profound role of interactions and find that under certain conditions the pair correlation may develop a global maximum at a finite interparticle separation due to the competition between repulsive interactions and thermal effects.

Coherent slowing of a supersonic beam with an atomic paddle.

We report the slowing of a supersonic beam by elastic reflection from a receding atomic mirror. We use a pulsed supersonic nozzle to generate a 511+/-9 m/s beam of helium that we slow by reflection from a Si(111)-H(1x1) crystal placed on the tip of a spinning rotor. We were able to reduce the velocity of helium by 246 m/s and show that the temperature of the slowed beam is lower than 250 mK in the comoving frame.

Quantum many-body culling: production of a definite number of ground-state atoms in a bose-einstein condensate.

We propose a method to produce a definite number of ground-state atoms by adiabatic reduction of the depth of a potential well that confines a degenerate Bose gas with repulsive interactions. Using a variety of methods, we map out the maximum number of particles that can be supported by the well as a function of the well depth and interaction strength, covering the limiting case of a Tonks gas as well as the mean-field regime. We also estimate the time scales for adiabaticity and discuss the recent observation of atomic number squeezing [Chuu, Phys. Rev. Lett. 95, 260403 (2005)10.1103/PhysRevLett.95.260403].

Experimental study of the role of atomic interactions on quantum transport.

We report an experimental study of quantum transport for atoms confined in a periodic potential and compare between thermal and Bose-Einstein condensation (BEC) initial conditions. We observe ballistic transport for all values of well depth and initial conditions, and the measured expansion velocity for thermal atoms is in excellent agreement with a single-particle model. For weak wells, the expansion of the BEC is also in excellent agreement with single-particle theory, using an effective temperature. We observe a crossover to a new regime for the BEC case as the well depth is increased, indicating the importance of interactions on quantum transport.

Compression of atomic phase space using an asymmetric one-way barrier.

We show how to construct asymmetric optical barriers for atoms. These barriers can be used to compress phase-space of a sample by creating a confined region in space where atoms can accumulate with heating at the single photon recoil level. We illustrate our method with a simple two-level model and then show how it can be applied to more realistic multilevel atoms.

A high frequency optical trap for atoms using Hermite-Gaussian beams.

We present an experimental method to create a single high frequency optical trap for atoms based on an elongated Hermite-Gaussian TEM01 mode beam. This trap results in confinement strength similar to that which may be obtained in an optical lattice. We discuss an optical setup to produce the trapping beam and then detail a method to load a Bose-Einstein Condensate (BEC) into a TEM01 trap. Using this method, we have succeeded in producing individual highly confined lower dimensional condensates.

Direct observation of sub-Poissonian number statistics in a degenerate bose gas.

We report the direct observation of sub-Poissonian number fluctuation for a degenerate Bose gas confined in an optical trap. Reduction of number fluctuations below the Poissonian limit is observed for average numbers that range from 300 to 60 atoms.

Guiding neuronal growth with light.

Control over neuronal growth is a fundamental objective in neuroscience, cell biology, developmental biology, biophysics, and biomedicine and is particularly important for the formation of neural circuits in vitro, as well as nerve regeneration in vivo [Zeck, G. & Fromherz, P. (2001) Proc. Natl. Acad. Sci. USA 98, 10457-10462]. We have shown experimentally that we can use weak optical forces to guide the direction taken by the leading edge, or growth cone, of a nerve cell. In actively extending growth cones, a laser spot is placed in front of a specific area of the nerve's leading edge, enhancing growth into the beam focus and resulting in guided neuronal turns as well as enhanced growth. The power of our laser is chosen so that the resulting gradient forces are sufficiently powerful to bias the actin polymerization-driven lamellipodia extension, but too weak to hold and move the growth cone. We are therefore using light to control a natural biological process, in sharp contrast to the established technique of optical tweezers [Ashkin, A. (1970) Phys. Rev. Lett. 24, 156-159; Ashkin, A. & Dziedzic, J. M. (1987) Science 235, 1517-1520], which uses large optical forces to manipulate entire structures. Our results therefore open an avenue to controlling neuronal growth in vitro and in vivo with a simple, noncontact technique.

State reconstruction of the kicked rotor.

We propose two experimentally feasible methods based on atom interferometry to measure the quantum state of the kicked rotor.

Observation of chaos-assisted tunneling between islands of stability.

We report the direct observation of quantum dynamical tunneling of atoms between separated momentum regions in phase space. We study how the tunneling oscillations are affected as a quantum symmetry is broken and as the initial atomic state is changed. We also provide evidence that the tunneling rate is greatly enhanced by the presence of chaos in the classical dynamics. This tunneling phenomenon represents a dramatic manifestation of underlying classical chaos in a quantum system.

Observation of the quantum zeno and anti-zeno effects in an unstable system.

We report the first observation of the quantum Zeno and anti-Zeno effects in an unstable system. Cold sodium atoms are trapped in a far-detuned standing wave of light that is accelerated for a controlled duration. For a large acceleration the atoms can escape the trapping potential via tunneling. Initially the number of trapped atoms shows strong nonexponential decay features, evolving into the characteristic exponential decay behavior. We repeatedly measure the number of atoms remaining trapped during the initial period of nonexponential decay. Depending on the frequency of measurements we observe a decay that is suppressed or enhanced as compared to the unperturbed system.

Shape of the quantum diffusion front.

We show that quantum diffusion has well-defined front shape. After an initial transient, the wave packet front (tails) is described by a stretched exponential P(x,t) = A(t)exp(-absolute value of [x/w](gamma)), with 1 < gamma < infinity, where w(t) is the spreading width which scales as w(t) approximately t(beta), with 0 < beta < or = 1. The two exponents satisfy the universal relation gamma = 1/(1-beta). We demonstrate these results through numerical work on one-dimensional quasiperiodic systems and the three-dimensional Anderson model of disorder. We provide an analytical derivation of these relations by using the memory function formalism of quantum dynamics. Furthermore, we present an application to experimental results for the quantum kicked rotor.

Optical billiards for atoms.

One of the central paradigms for classical and quantum chaos in conservative systems is the two-dimensional billiard in which particles are confined to a closed region in the plane, undergoing elastic collisions with the walls and free motion in between. We report the first realization of billiards using ultracold atoms bouncing off beams of light. These beams create the desired spatial pattern, forming an "optical billiard." We find excellent agreement between theory and our experimental demonstration of chaotic and stable motion in optical billiards, establishing a new testing ground for classical and quantum chaos.

Recovery of classically chaotic behavior in a noise-driven quantum system.

The quantum kicked rotor is studied in a regime of high amplitude noise. A transition to diffusive behavior is observed as dynamical localization, characterized by suppressed diffusion and exponential momentum distributions, is completely destroyed by noise. With increasing noise amplitude, further transition to classical behavior is shown through an accurate quantitative analysis, which demonstrates that both the energy growth and the momentum distributions are reaching their classical limits. The importance of short-time correlations in the recovery of classically chaotic behavior is discussed.

Dynamical localization of ultracold sodium atoms.

We report a study of atomic motion in time-dependent optical potentials. We measure momentum transfer in parameter regimes for which the classical dynamics are chaotic, and observe the quantum suppression of chaos by dynamical localization. The high degree of control over the experimental parameters enables detailed comparisons with theoretical predictions, and opens new avenues for investigating quantum chaos.

Progress at NIST toward absolute frequency standards using stored ions.

Experiments directed toward the realization of frequency standards of high accuracy using stored ions are briefly summarized. In one experiment, an RF oscillator is locked to a nuclear spin-flip hyperfine transition (frequency approximately 3.03x10(8) Hz) in (9 )Be(+) ions that are stored in a Penning trap and sympathetically laser-cooled. Stability is better than 3x10(-12)tau(-(1/2)) and uncertainty in Doppler shifts is estimated to be less than 5x10(-15). In a second experiment, a stable laser is used to probe an electric quadrupole transition (frequency approximately 1.07x10(15) Hz) in a single laser-cooled (199)Hg(+) ion stored in a Paul trap. The measured Q value of this transition is approximately 10(13). Future possible experiments are discussed.

Treatment of canine low pressure pulmonary edema. Nitroprusside versus hydralazine.

In canine oleic acid pulmonary edema, we investigated acute cardiopulmonary effects of different doses of nitroprusside and compared the results with those obtained after intravenously administered hydralazine. Oleic acid increased (p less than 0.05) intrapulmonary shunt (Qs/Qt), increased (p less than 0.01) systemic vascular resistance (SVR), and reduced (p less than 0.05) cardiac output (CO). In the presence of low-pressure pulmonary edema, low-dose nitroprusside (NP1) reduced (p less than 0.01) mean blood pressure (BP) approximately 8%, but with the exception of a small fall in ventricular filling pressure, other parameters remained constant. Compared with control values, a higher dose of nitroprusside (NP2) reduced mean BP 20%, and despite a fall (p less than 0.01) in pulmonary capillary wedge pressure, CO increased (p less than 0.05) 20%. Corresponding to the increase in flow, mean Qs/Qt increased (p less than 0.05) from 26 to 36% with NP2 and arterial O2 tension fell (186 to 166 mmHg, p less than 0.05). Compared with NP2, intravenously administered hydralazine caused a larger (p less than 0.01) change in CO. Despite increased CO and increased (p less than 0.01) mixed venous O2 tension, there was no deterioration in gas exchange with hydralazine. Mean Qs/Qt remained constant and arterial O2 tension, (PaO2) increased (p less than 0.05) from 174 mmHg to 217 mmHg. The increased CO with NP2 and hydralazine is probably explained by the large reduction in systemic vascular resistance. Because Qs/Qt remained constant with hydralazine, the increase in PaO2 is most likely due to the increase in PvO2, which increased because CO increased.(ABSTRACT TRUNCATED AT 250 WORDS)