Technical Activities

[skip navigation] NIST Physical Measurement Laboratory home page Technical Activities go to NIST home page NIST Physical Measurement Laboratory home page Products and Services Physical Reference Data Research Areas / Divisions Contact us Search the Physical Measurement Laboratory webspace

"Technical Activities  2005-2007" - Table of Contents

Division home page

Atomic Physics Division
The strategy of the Atomic Physics Division is to develop and apply atomic physics research methods, and particulary the interaction between atoms and electromagnetic fields, to achieve fundamental advances in measurement science--some at the quantum limit--relevant to industry and the technical community, and to produce and critically compile physical reference data.


GOAL: To determine
atomic properties and
investigate fundamental
quantum interactions

Strategic Focus Areas:

   

First

Light-Matter Interactions and Atom Optics  -  to advance the physics of electromagnetic-matter interactions, to explore new applications for laser cooled and trapped atoms, to study exotic states of matter, and to study and control many-body quantum systems.

Second

Nanoscale and Quantum Metrology  -  to advance measurement science at the atomic and nanometer scale, focusing on precision optical metrology, quantum devices, nanoscale plasmas and nanooptical systems.

Third

Critically Evaluated Atomic Data  -  to produce reference data on atomic structure, to critically compile reference data for scientific and technological applications, and to develop techniques to apply the data to further the understanding of important plasma devices.

Light-Matter Interactions and Atom Optics:

to advance the physics of electromagnetic-matter interactions, to explore new applications for laser cooled and trapped atoms, to study exotic states of matter, and to study and control many-body quantum systems.

INTENDED OUTCOME AND BACKGROUND

This strategic element focuses on the physics of laser cooling and electromagnetic trapping of neutral particles, the manipulation of Bose-Einstein condensates (BECs), and the use of optical dipole forces as a new tool for analyzing of microscopic objects in biochemistry. It includes both fundamental and applied studies, such as developing measurement techniques for biomolecular systems and developing a quantum information processor. A strong theoretical-experimental collaboration is aimed at interpreting experimental results and providing guidance for new experiments.

The development of laser cooling and trapping techniques allows exquisite control over the motion of atoms. Such control has been exploited to build more precise atomic clocks and gravity gradiometers. These techniques also enable the study and manipulation of atoms and molecules under conditions in which their quantum or wave behavior dominates. This research has revolutionized the field of matter-wave optics.

Theoretically and experimentally, our programs aims to understand and exploit: Bose-Einstein condensation of neutral atoms; matter-wave optics; optical and magnetic control of trapped, ultracold atom collisions; advanced laser cooling and collision studies for atomic clocks; the quantum behavior of atoms in optical lattices, including studies in one-, two-, and three-dimensional systems, and simulation of condensed matter models with cold atoms; quantum information processing; quantum computing architectures; and optical characterization and manipulation of single molecules, biomolecules, and biomembranes.

The Atomic Physics Division is at the center of the newly established Joint Quantum Institute between the NIST Physics Laboratory, the Physics Department of the University of Maryland, and the Laboratory of Physical Sciences of the National Security Agency. The Chief of the Atomic Physics Division also coordinates NIST’s program in quantum information science, which includes activities in the Physics Laboratory, the Electronic and Electrical Engineering Laboratory, and the Information Technology Laboratory.

Accomplishments

    Quantum SWAP Operation with Neutral Atoms as Qubits

        Figure 1

    Figure 1. Artist’s conception of pairs of opposite-spin atoms (qubits) brought together in an optical lattice to be entangled by their atom-atom interactions.

    Two outstanding problems in neutral atom quantum computing have been the ability to address atoms in an optical lattice and the demonstration of controlled two-atom interactions. We have used a novel, two-period lattice to demonstrate both processes.

    In one experiment, published in Physical Review Letters, we used the state-dependent, two-period “double well” lattice to selectively address the spins (acting as qubits) in only one of the sublattices, despite the wells being only 400 nm from each other. In another experiment, published in Nature, we used the double well to isolate and control pairs of atoms, forcing them to interact in a state-dependent manner (making use of quantum exchange symmetry) that gives rise to the entanglement needed for quantum computing. These experiments were both the first of their kind, and represent a significant step forward for neutral atom quantum computing.


    CONTACT: Dr. James (Trey) Porto
    (301) 975-3238
    trey.porto@nist.gov



  • Control of Cold Quantum Gases

        Figure 2

    Figure 2. The different regimes for cold-collision photoassociation. Here tρ is the time scale on which the overall density of the gas evolves when the light is turned on, tϖ is the time scale for coherent oscillations between atomic and molecular populations, tA is time scale over which the transient response to the turning on of the light is completed, and tϒ is the time scale for spontaneous emission of light by the excited molecules.

    Many recent atomic physics experiments have used magnetic-field control of scattering resonances to modify the properties and dynamics of ultracold, atomic quantum gases such as Bose-Einstein condensates or mixtures of fermions. These resonances occur when the energy of a bound state of two atoms is tuned to the same energy as that of two separated cold atoms. Such resonances can be used to make cold molecules and molecular Bose-Einstein condensates, to strongly modify the nature of superfluid atom pairing, and to modify the properties of atoms trapped in optical lattices. Such phenomena are relevant to fundamental physics, condensed matter (solid state) physics, atomic clocks, and quantum information.

    We have quantitatively characterized such resonances for a number of ultracold gases and developed simple physical models for understanding them. Recent work has characterized optically induced scattering resonances for laser control of quantum gases of alkaline earth species such as Sr or Yb, which are of great interest for next-generation atomic clocks. One specific application has been to the temporal dynamics of an atomic Bose-Einstein condensate when pairs of atoms are converted into molecules by photoassociation. We identify three main photoassociation regimes that can be understood on the basis of time-dependent two-body theory. In particular, the so-called rogue dissociation regime, which has a density-dependent limit on the photoassociation rate, is identified with a transient regime of the two-atom dynamics. We have determined how the various regimes could be explored by photoassociating condensates of alkaline-earth atoms.


    CONTACT: Dr. Paul S. Julienne
    (301) 975-2596
    paul.julienne@nist.gov



  • Coherent Optical Generation of Vortices in a Bose-Einstein Condensate

        Figure 3

    Figure 3. Absorption image of a Na BEC vortex state, taken along the axis of the LG beam, generated by transferring h of optical orbital angular momentum to each BEC atom.

    We have developed a new, well-controlled, coherent method of vortex creation. Light can carry both “spin” angular momentum, associated with its polarization and “orbital” angular momentum (OAM) associated with its stial mode. In particular, Laguerre-Gauss (LG, donut) modes of laser beams carry OAM per photon quantized in units of h.

    In work published in Physical Review Letters we used a two-photon Raman process to induce BEC atoms to coherently absorb the OAM of an LG beam, creating a vortex. We verified the coherence of the process by creating and interfering superpositions of different vortex states, showing that the relative phase between the states is determined by the relative phase of the optical fields. We also created vortices of higher angular momentum by transferring to each atom the orbital angular momentum of two photons.


    CONTACT: Dr. Kristian Helmerson
    (301) 975-4266
    kristian.helmerson@nist.gov



  • A Quantum Phase Transition with Cold Atoms

    The Mott insulator is a remarkable phase of matter, where the interactions between atoms in an optical lattice lead to a state with an exact number of atoms per lattice site (e.g., one). This state is central to our quantum information program where the Mott state is the initial state. Any deviation from one atom per site will decrease the fidelity of subsequent quantum gates.

    To extend our understanding of Mottinsulator physics we recently undertook a detailed study of the insulating phase in a 2-D system. (A 1-D optical lattice divides the system into an array of 2-D subsystems, and a second 2-D lattice provides a corrugated potential in each subsystem.) This work, published in Physical Review Letters, focused on the momentum distribution of the atoms, finding that in the insulating phase the distribution agreed quantitatively with theory. In addition, we probed the size of the insulating region by measuring correlations in the noise of atom cloud images.

    Figure 4. Momentum (a) and noise correlations (b) in a 2-D Mott insulating system, in units of single-photon recoil momentum.

    Figure 4

    CONTACT: Dr. Ian Spielman
    (301) 975-8664
    ian.spielman@nist.gov



  • Relative-Intensity-Squeezed Light for Measurement and Quantum Applications

      Figure 5

    Figure 5. Squeezing versus transmission and gain. The solid spheres show the squeezing measured at 1 MHz, for different cell temperatures, 109 °C (blue), 112 °C (red), and 114 °C (black), as the detuning of the pump laser is scanned. The projection onto the x-yplane shows contour lines of the theoretical squeezing at 2 dB intervals from +4 to –8 dB, and the projections of the data points.

    We have discovered a nonlinear optical scheme (nondegenerate four-wave mixing) that robustly generates strongly squeezed light in a simple Rb vapor cell. This technique represents an important advance over the best previous atomic vapor results (-2.2 dB for vacuum quadrature squeezing), and presents new opportunities both in purely optical experiments (e.g., quantum optics, interferometry for precision measurements) and in light-atom interactions (e.g., quantum atom optics, and precision spectroscopy).

    We create two light beams whose intensity difference is squeezed by -8 dB (noise ≈ 15 % of the usual shot noise). We have demonstrated low (detection) frequency squeezing down to below 5 kHz, a remarkable feat considering that OPO technology took about 15 years to demonstrate this. The light is narrowband and nearly resonant with the Rb atomic transition.

    This light should be particularly useful in “quantum atom optics” experiments where we will interact nonclassical light with atoms to produce nonclassical matter-wave beams. We also foresee applications to atomic “quantum memory” applications for quantum information processing.


    CONTACT: Dr. Paul Lett
    (301) 975-6559
    paul.lett@nist.gov



  • Relative-Intensity-Squeezed Light for Measurement and Quantum Applications

    Nanotubes, like the carbon tubes used in high-strength materials, are among the most promising structures in nanotechnology. Naturally occurring phospholipid and protein nanotubes can transport genetic material between cells, viruses, and bacteria. Transport of biological molecules through nanotubes is a particularly exciting prospect for biotechnology applications.

    We have created robust, biocompatible nanotubes by directed self-assembly. Starting with a polymer vesicle (polymersome) having a hydrophilic/hydrophobic bilayer membrane, we use optical tweezers (a focused laser beam that grabs dielectric material) to pull on the membrane. Polymer molecules in the distorted membrane rearrange to form long polymer nanotubes, which we stabilize by chemical cross-linking.

    The nanotubes have a water-filled core approximately 80 nm in diameter and are up to 1 cm long. Optical tweezers manipulation creates networks of nanotubes and vesicles, systems that hold promise for nanofluidics and other biotech applications. The results were published in the Proceedings of the National Academy of Sciences.

        Figure 6

    Figure 6. From left to right, an optical tweezer pulls a nanotube from the left side of a polymersome at -10 μm/s. The white scale bar at left indicates 10 μm.


    CONTACT: Dr. Kristian Helmerson
    (301) 975-4266
    kristian.helmerson@nist.gov


First strategic focus   |   Second strategic focus   |   Third strategic focus

"Technical Activities  2005-2007" - Table of Contents