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.
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GOAL: To determine
atomic properties and
investigate fundamental
quantum interactions |
Strategic Focus Areas: |
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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. |
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.
Our research includes theoretical and experimental projects that contribute to
the understanding and exploitation of: Bose-Einstein condensation of neutral
atoms; matter-wave optics; optical and magnetic control of trapped-atom
collisions; advanced laser cooling and collision studies for atomic clocks; the
quantum behavior of atoms in optical lattices, including in low dimensionality;
the superfluid to Mott-insulator quantum phase transition; quantum information
processing; quantum-computing architectures; and optical characterization and
manipulation of single molecules, biomolecules, and
biomembranes.
Accomplishments
Control of Cold Quantum Gases
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Figure 1. Lifetime of the tunable, molecular
bound state of the 85Rb2 dimer as a
magnetic field B is varied near a scattering resonance at
15.2 mT. The rapid increase in lifetime is due
to the dramatic increase in the size of the
weakly bound atom-pair, to hundreds of nanometers,
as the field gets closer to the resonance value.
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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 applied quantum mechanical
models to quantitatively characterize
such resonances and to develop simple
physical models for understanding
them. These have been applied to give
good agreement with data and predictive
power for bosonic species 85Rb (see
Fig. 1) and 133Cs, and for fermionic
species 6Li and 40K. We have also
initiated studies on optically induced scattering
resonances for laser control of quantum
gases of alkaline earth species such
as Ca or Sr, which are of great interest
for next-generation atomic clocks.
Spectroscopy of Na2
Molecules in the Lowest
Triplet State
We have used the technique of two-color
photoassociation spectroscopy
(two colliding atoms absorbing photons
to create a diatomic molecule) to
improve the spectroscopy of the lowest
triplet state of the Na2 molecule. The
spectra obtained represent a factor of
1000 improvement in resolution over
the previously obtained spectra of this
state, and include a number of previously
unobserved vibrational levels, as well
as unresolved hyperfine and fine structure.
This knowledge has altered our
view of the angular momentum coupling
scheme that must be used to
represent this state of the molecule.
Knowledge of the interaction potentials
between two sodium atoms, at the level
of detail that can be obtained by
photoassociation spectroscopy, is
required to predict the behavior of this
prototype system of two colliding, effectively
single-electron atoms. Improved
theory in this area is necessary for
understanding many experiments in
atomic and molecular physics, and is
especially pertinent for current studies
of atomic and molecular Bose-Einstein
condensates.
Optical Manipulation of
Nanocontainers for
Biotechnology
In collaboration with researchers in
CSTL and CARB, we are developing
optical techniques for manipulating
nanocontainers (containers with femto-liter
volumes of fluids), to perform
ultrasmall volume chemistry and to
isolate and sort single molecules.
We are currently investigating three systems,
liposomes, polymersomes, and
hydrosomes, for use as nanocontainers.
Liposomes and polymersomes are closed
structures composed of a lipid and polymer
membrane, respectively, typically
about 10 micrometers in diameter. The
membrane acts as a barrier to separate
an aqueous interior environment from
an aqueous exterior environment.
Hydrosomes are micrometer-sized, surfactant-stabilized
water droplets that reside in a fluorocarbon environment.
The techniques we use include optical
tweezers, for trapping and remotely
moving the nanocontainers, and an
"optical scalpel," for opening membranes
in order to induce fusion of
liposomes and polymersomes. (See
Fig. 2.) In all three systems, we are
able to bring together two similar
nanocontainers using optical trapping
and to subsequently fuse them together,
allowing their contents to mix.
We have demonstrated the use of liposomes
and hydrosomes in performing
controlled, elementary chemical reactions.
We are currently investigating the
application of these nanocontainers for
single-molecule studies and single-molecule
sorting.
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Figure 2. Time sequence of video microscopy images showing
two liposomes, brought into contact with optical tweezers and induced
to fuse by an optical scalpel, a pulsed ultraviolet laser focused on
the contact point, which initiates the fusion (a). Images (b),
(c), and (d) were taken 132 ms, 264 ms,
and 528 ms later, respectively.
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Neutral-Atom Quantum
Information
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Figure 3. As the 3-D lattice depth is
increased, the tunneling between lattice sites
decreases. At a lattice depth of around 10 recoil
energies, the system undergoes the Mott transition,
and the diffraction pattern disappears. The transition
is reversible, and the diffraction reappears when
the lattice depth is reduced.
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Single atoms can act as qubits for quantum
information (QI) using, for example,
the internal hyperfine and Zeeman
states as the qubit states. Our approach
to neutral-atom QI is to hold and
manipulate the atoms using laser fields
for trapping and transporting. An optical
lattice provides a natural register for
atomic qubits. A BEC loaded adiabatically
into an optical lattice provides,
potentially, millions of qubits initialized
in their ground states, since the BEC,
or at least the condensed fraction, is
initially in the ground state.
If a noninteracting BEC is slowly loaded
into an optical lattice, the typical result
is that the coherent wavefunction of
each atom is spread across all the available
lattice sites, so that there is a statistical
(Poissonian) fluctuation in the
number of atoms in any given site. If,
however, there are repulsive interactions,
at some lattice depth the competition
between tunneling and the on-site
repulsive interaction favors the ground
state being one (or some fixed number
of) atom(s) per lattice site. This is a
phase transition known as the Mott
insulator transition because the system
goes from being superfluid (at large
tunneling rate) to insulating (at small tunneling).
We observe the phase transition for Rb
atoms in a three-dimensional optical lattice
by looking at the diffraction pattern
formed by the atoms upon release from
the lattice. As shown in Fig. 3, well-resolved
diffraction indicates phase
coherence across the lattice, and therefore
an uncertain atom number in each
site. The disappearance of the diffraction
pattern is characteristic of a fixed number
per site, and therefore an uncertain
phase difference from site to site, indicative
of being in the insulator state.
First strategic focus |
Second strategic focus |
Third strategic focus
"Technical Activities 2004" - Table of Contents |
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