the development of ultracold atom technology, in particular the use of coherent matter waves in sensors, atom interferometers, and quantum information processing devices.
INTENDED OUTCOME AND BACKGROUND
This program provides measurements and data to enable 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 experimental program develops deterministic atom-delivery systems,
i.e., devices that can deliver precisely one atom to a predetermined
location, on demand. In addition, the Division is developing a testbed
for quantum communication systems, together with the Atomic Physics
Division and the Information Technology Laboratory.
Accomplishments
Quantum Key Distribution System Operating at a Sifted-Key Rate Over 4 Mbit/s
We have collaborated with NIST’s Advanced Network Technologies Division in developing a complete fiber-based, polar-ization-encoded quantum key distribution (QKD) system based on the Bennett-Brassard protocol (BB84). The system operates at a clock rate of 1.25 GHz, and is capable of producing key bits from quantum-channel transmissions (sifted key) at rates above 4 Mbit/s over 1 km of optical fiber. This output can be processed to produce unconditionally secure cryptographic key for encrypting messages.
Our results represent a new record in the operational output rate of a QKD system based on single-photon transmission. They are made possible by the integration of quantum cryptography protocols with classical high-speed telecommunications techniques. The quantum channel uses 850 nm photons from attenuated high-speed vertical cavity surface-emitting lasers (VCSELs), and the classical channel uses 1550 nm light from normal commercial coarse wavelength division multiplexing devices. A polarization auto-compensation module has been developed and utilized to recover the polarization state and to compensate for temporal drift. An automatic timing alignment device has also been developed to quickly handle the initial configuration of quantum channels so that detection events fall into the correct timing window. These automated functions make the system more practical for integration into existing optical local area networks.
We are developing a free-space optical QKD system operating at the Balmer alpha wavelength of 656 nm, where light from the sun is attenuated by 7 dB in a narrow interval, which is advantageous for daylight operation of free-space QKD systems. We are also developing semiconductor optical waveguides as a source of correlated photon pairs, in collaboration with the Laboratory for Physical Sciences of the University of Maryland.
‘March Madness’ Effects Observed in Ultracold Gases
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Figure 6. Representation of the interference of wave patterns created by atoms that have been released from an optical lattice with disorder. The complex shape of peaks and valleys is an example of a natural fractal pattern, a pattern that ocntinues to reveal new details no matter how many times it is magnified. |
We have discovered new quantum phases in ultracold gases that reveal the competition
between two major mechanisms of electrical resistance in solids: crystalline disorder, and the interactions
between electrons. In “March Madness” terms, basketball fans who arrive early to an empty stadium can move
relatively quickly down any row unless they encounter a railing, wall, or other barrier (analogous to crystal
disorder). But once the game begins, a fan’s movements are constrained along rows by other fans already
occupying seats (analogous to electron blocking). Even though Phillip Anderson and Sir Neville Mott won
Nobel Prizes in 1977 for the theory of these phenomena in metals, it has been difficult to observe their
effects in real materials.
Quantum phases of hard-core bosons confined
in a one-dimensional quasiperiodic potential were studied within the theoretical
framework of intensity interferometry (Hanbury Brown-Twiss interferometry). The quasiperiodic potential induces a cascade
of Mott-like band-insulator phases, in addition to the more familiar Mott insulator,
Bose glass, and superfluid phases. The new phases are incompressible and have zero superfluid fraction. At critical filling factors, the appearance of these insulating phases is heralded by a peak to dip transition
in the interferogram, which reflects the fermionic aspect of hard core bosons. In the localized phase, the interference pattern exhibits a hierarchy of peaks at the reciprocal lattice vectors of the system. Our study demonstrates that, in contrast to measurements of the momentum distribution,
intensity interferometry provides an effective method to distinguish Mott and glassy phases.
First strategic focus |
Second strategic focus |
Third strategic focus
"Technical Activities 2005-2007" - Table of Contents |
