357 research outputs found
Ultrafast slow-light: Raman-induced delay of THz-bandwidth pulses
We propose and experimentally demonstrate a scheme to generate
optically-controlled delays based on off-resonant Raman absorption. Dispersion
in a transparency window between two neighboring, optically-activated Raman
absorption lines is used to reduce the group velocity of broadband 765 nm
pulses. We implement this approach in a potassium titanyl phosphate (KTP)
waveguide at room temperature, and demonstrate Raman-induced delays of up to
140 fs for a 650-fs duration, 1.8-THz bandwidth, signal pulse; the available
delay-bandwidth product is . Our approach is applicable to single
photon signals, offers wavelength tunability, and is a step toward processing
ultrafast photons.Comment: 5+4 pages, 4+2 figure
Switched wave packets: A route to nonperturbative quantum control
The dynamic Stark effect due to a strong nonresonant but nonionizing laser field provides a route to quantum control via the creation of novel superposition states. We consider the creation of a field-free "switched" wave packet through adiabatic turn-on and sudden turn-off of a strong dynamic Stark interaction. There are two limiting cases for such wave packets. The first is a Raman-type coupling, illustrated by the creation of field-free molecular axis alignment. An experimental demonstration is given. The second case is that of dipole-type coupling, illustrated by the creation of charge localization in an array of quantum wells
Time-bin to Polarization Conversion of Ultrafast Photonic Qubits
The encoding of quantum information in photonic time-bin qubits is apt for
long distance quantum communication schemes. In practice, due to technical
constraints such as detector response time, or the speed with which
co-polarized time-bins can be switched, other encodings, e.g. polarization, are
often preferred for operations like state detection. Here, we present the
conversion of qubits between polarization and time-bin encodings using a method
that is based on an ultrafast optical Kerr shutter and attain efficiencies of
97% and an average fidelity of 0.827+/-0.003 with shutter speeds near 1 ps. Our
demonstration delineates an essential requirement for the development of hybrid
and high-rate optical quantum networks
Observation of high-order quantum resonances in the kicked rotor
Quantum resonances in the kicked rotor are characterized by a dramatically
increased energy absorption rate, in stark contrast to the momentum
localization generally observed. These resonances occur when the scaled
Planck's constant hbar=(r/s)*4pi, for any integers r and s. However only the
hbar=r*2pi resonances are easily observable. We have observed high-order
quantum resonances (s>2) utilizing a sample of low temperature, non-condensed
atoms and a pulsed optical standing wave. Resonances are observed for
hbar=(r/16)*4pi r=2-6. Quantum numerical simulations suggest that our
observation of high-order resonances indicates a larger coherence length than
expected from an initially thermal atomic sample
Multifaceted Faculty Network Design and Management: Practice and Experience Report
We report on our experience on multidimensional aspects of our faculty's
network design and management, including some unique aspects such as
campus-wide VLANs and ghosting, security and monitoring, switching and routing,
and others. We outline a historical perspective on certain research, design,
and development decisions and discuss the network topology, its scalability,
and management in detail; the services our network provides, and its evolution.
We overview the security aspects of the management as well as data management
and automation and the use of the data by other members of the IT group in the
faculty.Comment: 19 pages, 11 figures, TOC and index; a short version presented at
C3S2E'11; v6: more proofreading, index, TOC, reference
Coherent Control and Entanglement in the Attosecond Electron Recollision Dissociation of D2+
We examine the attosecond electron recollision dissociation of D2+ recently
demonstrated experimentally [H. Niikura et al., Nature (London) 421, 826
(2003)] from a coherent control perspective. In this process, a strong laser
field incident on D2 ionizes an electron, accelerates the electron in the laser
field to eV energies, and then drives the electron to recollide with the parent
ion, causing D2+ dissociation. A number of results are demonstrated. First, a
full dimensional Strong Field Approximation (SFA) model is constructed and
shown to be in agreement with the original experiment. This is then used to
rigorously demonstrate that the experiment is an example of coherent pump-dump
control. Second, extensions to bichromatic coherent control are proposed by
considering dissociative recollision of molecules prepared in a coherent
superposition of vibrational states. Third, by comparing the results to similar
scenarios involving field-free attosecond scattering of independently prepared
D2+ and electron wave packets, recollision dissociation is shown to provide an
example of wave-packet coherent control of reactive scattering. Fourth, this
analysis makes clear that it is the temporal correlations between the continuum
electron and D2+ wave packet, and not entanglement, that are crucial for the
sub-femtosecond probing resolution demonstrated in the experiment. This result
clarifies some misconceptions regarding the importance of entanglement in the
recollision probing of D2+. Finally, signatures of entanglement between the
recollision electron and the atomic fragments, detectable via coincidence
measurements, are identified
Time Scaling and Frequency Invariant Multiresolution Analysis of Ultrasonic NDE Signals
Nuclear power plant pipes are periodically inspected for possible cracks that occur in the heat-affected zones of welds. Intergranular stress corrosion cracks (IGSCC) are the most common type of cracks encountered particularly in stainless steel piping. Three major factors are required for the formation and propagation of IGSCCs, the tensile stress on the inner diameter of the weld region, a corrosive environment and a sensitized grain structure. When these flaws are not detected early enough, the consequences can be disastrous, and therefore the detection of IGSCCs is of significant interest to the nuclear industry
Potential for ultrafast dynamic chemical imaging with few-cycle infrared lasers
We studied the photoelectron spectra generated by an intense few-cycle
infrared laser pulse. By focusing on the angular distributions of the back
rescattered high energy photoelectrons, we show that accurate differential
elastic scattering cross sections of the target ion by free electrons can be
extracted. Since the incident direction and the energy of the free electrons
can be easily changed by manipulating the laser's polarization, intensity, and
wavelength, these extracted elastic scattering cross sections, in combination
with more advanced inversion algorithms, may be used to reconstruct the
effective single-scattering potential of the molecule, thus opening up the
possibility of using few-cycle infrared lasers as powerful table-top tools for
imaging chemical and biological transformations, with the desired unprecedented
temporal and spatial resolutions.Comment: 16 pages, 6 figure
The genetic architecture of colonization resistance in Brachypodium distachyon to non-adapted stripe rust (Puccinia striiformis) isolates
Multilayered defense responses ensure that plants are hosts to only a few adapted pathogens in the environment. The host range of a plant pathogen depends on its ability to fully overcome plant defense barriers, with failure at any single step sufficient to prevent life cycle completion of the pathogen. Puccinia striiformis, the causal agent of stripe rust (=yellow rust), is an agronomically important obligate biotrophic fungal pathogen of wheat and barley. It is generally unable to complete its life cycle on the non-adapted wild grass species Brachypodium distachyon, but natural variation exists for the degree of hyphal colonization by Puccinia striiformis. Using three B. distachyon mapping populations, we identified genetic loci conferring colonization resistance to wheat-adapted and barley-adapted isolates of P. striiformis. We observed a genetic architecture composed of two major effect QTLs (Yrr1 and Yrr3) restricting the colonization of P. striiformis. Isolate specificity was observed for Yrr1, whereas Yrr3 was effective against all tested P. striiformis isolates. Plant immune receptors of the nucleotide binding, leucine-rich repeat (NB-LRR) encoding gene family are present at the Yrr3 locus, whereas genes of this family were not identified at the Yrr1 locus. While it has been proposed that resistance to adapted and non-adapted pathogens are inherently different, the observation of (1) a simple genetic architecture of colonization resistance, (2) isolate specificity of major and minor effect QTLs, and (3) NB-LRR encoding genes at the Yrr3 locus suggest that factors associated with resistance to adapted pathogens are also critical for non-adapted pathogens
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