| Coherent Matter-Wave and Quantum Information Processing
Metrology
INTENDED OUTCOME AND
BACKGROUND
The intended outcome of this program is to provide measurements and data needed
for the development of ultracold atom technology, in particular the use of
coherent matter waves in sensors, atom interferometers, and quantum information
processing devices.
The Division maintains two efforts in this area, one theoretical and one
experimental. The theoretical program is focused on quantitative modeling of
degenerate quantum gases, with particular attention to the dynamics of
Bose-Einstein condensates subject to external forces, e.g., manipulation of
condensates confined in an optical lattice. This program is an outgrowth of
extensive collaborations with experimental groups at NIST, JILA, and elsewhere,
begun in the mid-1990s.
The primary goal of the experimental program is the development of
deterministic atom-delivery systems, i.e., devices that can deliver one and
only one atom to a predetermined location, on demand. In addition, the Division
is a partner in a project to develop a testbed for quantum-communication
systems, together with the Atomic Physics Division and the Information
Technology Laboratory.
Accomplishments
Coherent Matter-Wave Device Physics
The development of coherent matter-wave sources, based on Bose-Einstein
condensates of dilute atomic gases, has opened up a new frontier of precision
measurement. There are long-range prospects for the use of such sources for
sensitive gravitational and inertial sensors, direct-write atomic lithography,
and quantum information processing. In collaboration with experimental programs
in Gaithersburg and Boulder, we work on quantitative studies of the dynamics of
coherent matter-wave systems, with a particular focus on first-principles
modeling and simulation of their dynamics.
Figure 13. Two-dimensional optical lattice potential (left), and its
associated lowest Wannier state (right). Potential and density distributions
are shown. |
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One subject of current interest is the dynamics of ultracold atoms in optical
lattices, a candidate system for quantum information processing. Optical
lattices are defect-free crystal potentials. Solid-state crystal structures
tend to favor certain types of lattices and their actual potentials are very
complex. Optical lattices, in contrast, are completely controllable, with the
potentials being perfectly sinusoidal; or, in general, a sum of sinusoidal
potentials.
We have calculated the band structure for 2D and 3D optical lattices for
parameter regimes appropriate to the experiments at NIST. The energy
eigenstates determined by these calculations, known as Bloch states, are useful
for calibrating lattice properties (e.g., beam orientation and depth).
As a case study, we investigated the types of lattices that can be prepared for
a 2D system made by three light fields in the plane. We showed that, for this
simple arrangement, all five types of 2D lattices can be made (square,
rectangular, centered rectangular, oblique, and hexagonal).
Atoms on Demand
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Figure 14. Atoms on demand; the chance of having exactly one atom goes
from the random-walk value of 37 % to a value near 100 % by the
application of feedback. |
Nanotechnology deals with understanding and manipulating matter on the
nanometer scale - that is, on the scale of a few tens of atoms to a few
hundred atoms. As we gain skill and knowledge in this regime, the natural
question arises, can we go further? Can tools be developed that work
controllably with single atoms individually, and, if so, what new science and
applications will become available?
With these questions in mind, we have recently developed a way to reliably
isolate one - and only one - atom, essentially "on demand."
Using laser cooling and trapping techniques, we have isolated single, cold
chromium atoms in a magneto-optical trap, and used feedback control over the
loading and loss processes to eliminate nearly all the random fluctuations in
trap occupation number that would ordinarily plague such a trap.
The result is a source in which single atoms can be extracted and replenished
reliably at rates ranging from several tens of atoms per second in the current
configuration to several hundred per second or more in the theoretical limit.
Applications for these deterministically produced atoms range from fundamental
studies of quantum coherence, which take advantage of the purely quantum nature
of isolated atoms, to structured doping of nanostructures, in which a small,
countable number of dopant atoms is required in nanostructures to tailor their
electronic, magnetic, or optical properties.
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