16 research outputs found
ac Stark shift and multiphoton-like resonances in low-frequency driven optical lattices
We suggest that Bose-Einstein condensates in optical lattices subjected to ac
forcing with a smooth envelope may provide detailed experimental access to
multiphoton-like transitions between ac-Stark-shifted Bloch bands. Such
transitions correspond to resonances described theoretically by avoided
quasienergy crossings. We show that the width of such anticrossings can be
inferred from measurements involving asymmetric pulses. We also introduce a
pulse tracking strategy for locating the particular driving amplitudes for
which resonances occur. Our numerical calculations refer to a currently
existing experimental set-up [Haller et al., PRL 104, 200403 (2010)].Comment: 5 pages, 6 figure
Generalized acceleration theorem for spatiotemporal Bloch waves
A representation is put forward for wave functions of quantum particles in
periodic lattice potentials subjected to homogeneous time-periodic forcing,
based on an expansion with respect to Bloch-like states which embody both the
spatial and the temporal periodicity. It is shown that there exists a
generalization of Bloch's famous acceleration theorem which grows out of this
representation and captures the effect of a weak probe force applied in
addition to a strong dressing force. Taken together, these elements point at a
"dressing and probing" strategy for coherent wave-packet manipulation, which
could be implemented in present experiments with optical lattices.Comment: 12 pages, 4 figure
Controlled wave-packet manipulation with driven optical lattices
Motivated by recent experimental progress achieved with ultracold atoms in
kilohertz-driven optical lattices, we provide a theoretical discussion of
mechanisms governing the response of a particle in a cosine lattice potential
to strong forcing pulses with smooth envelope. Such pulses effectuate adiabatic
motion of a wave packet's momentum distribution on quasienergy surfaces created
by spatiotemporal Bloch waves. Deviations from adiabaticity can then
deliberately be exploited for exerting coherent control and for reaching target
states which may not be accessible by other means. As one particular example,
we consider an analog of the \pi-pulses known from optical resonance. We also
suggest adapting further techniques previously developed for controlling atomic
and molecular dynamics by laser pulses to the coherent control of matter waves
in shaken optical lattices.Comment: 11 pages, 10 figure
PNA microarrays for hybridisation of unlabelled DNA samples
Several strategies have been developed for the production of peptide nucleic acid (PNA) microarrays by parallel probe synthesis and selective coupling of full-length molecules. Such microarrays were used for direct detection of the hybridisation of unlabelled DNA by time-of-flight secondary ion mass spectrometry. PNAs were synthesised by an automated process on filter-bottom microtitre plates. The resulting molecules were released from the solid support and attached without any purification to microarray surfaces via the terminal amino group itself or via modifications, which had been chemically introduced during synthesis. Thus, only full-length PNA oligomers were attached whereas truncated molecules, produced during synthesis because of incomplete condensation reactions, did not bind. Different surface chemistries and fitting modifications of the PNA terminus were tested. For an examination of coupling selectivity, bound PNAs were cleaved off microarray surfaces and analysed by MALDI-TOF mass spectrometry. Additionally, hybridisation experiments were performed to compare the attachment chemistries, with fully acetylated PNAs spotted as controls. Upon hybridisation of unlabelled DNA to such microarrays, binding events could be detected by visualisation of phosphates, which are an integral part of nucleic acids but missing entirely in PNA probes. Overall best results in terms of selectivity and sensitivity were obtained with thiol-modified PNAs on maleimide surfaces