Coherent control using adaptive learning algorithms

We have constructed an automated learning apparatus to control quantum systems. By directing intense shaped ultrafast laser pulses into a variety of samples and using a measurement of the system as a feedback signal, we are able to reshape the laser pulses to direct the system into a desired state. The feedback signal is the input to an adaptive learning algorithm. This algorithm programs a computer-controlled, acousto-optic modulator pulse shaper. The learning algorithm generates new shaped laser pulses based on the success of previous pulses in achieving a predetermined goal.Comment: 19 pages (including 14 figures), REVTeX 3.1, updated conten

PTPBR7 Binding Proteins in Myelinating Neurons of the Mouse Brain

Abstract Mouse protein tyrosine phosphatase PTPBR7 is a receptor-like, transmembrane protein that is localized on the surface of neuronal cells. Its protein phosphatase activity is reduced upon multimerization, and PTPBR7-deficient mice display motor coordination defects. Extracellular molecules that may influence PTPBR7 activity, however, remain to be determined. We here show that the PTPBR7 extracellular domain binds to highly myelinated regions in mouse brain, in particular the white matter tracks in cerebellum. PTPBR7 deficiency does not alter this binding pattern, as witnessed by RAP in situ staining of Ptprr -/-mouse brain sections. Additional in situ and in vitro experiments also suggest that sugar moieties of heparan sulphate and chondroitin sulphate glycosaminoglycans are not critical for PTPBR7 binding. Candidate binding proteins were affinity-purified exploiting the PTPBR7 extracellular domain and identified by mass spectrometric means. Results support the suggested link between PTPRR isoforms and cerebellar calcium ion homeostasis, and suggest an additional role in the process of cell-cell adhesion

Femtosecond Real-Time Probing of Reactions. 6. A Joint Experimental and Theoretical Study of 8I_2 Dissociation

The dynamics of the ultraviolet photofragmentation of bismuth dimer are studied experimentally and theoretically in the time domain. Employing the technique of femtosecond transition-state spectroscopy, the evolution of the dissociative process along two reaction channels leading to the 6p^3(^4S^0_(3/2) + 6p^3(^2D^0_(3/2) and 6p^3(^4S^0_(3/2)) + 6p^3(^D^0_(5/2)) levels of the atomic products is investigated following initial excitation of Bi_2 at λ. = 308 nm. The broad spectral width of the ultrashort probe laser pulse coupled with the closely spaced excited energy levels of Bi enables fluorescence via some 14 atomic transitions to be monitored in real time, rendering possible the detection of dissociating molecules at different internuclear separations on the controlling potential surfaces. Long-time detection of the ^2D^0_(3/2) spin-orbit level permits clocking of the reaction along the lower energy exit channel, for which we report a dissociation time τ_(1/2) of approximately 1 ps, at which time the product Bi atoms are separated by some 10.7 Å. Analogous measurements for the reaction giving rise to the higher-lying J = 5/2 level of the ^2D_j term yield a value of τ_(1/2) = 1.5 ps, corresponding to an interfragment distance of 7.5 Å. From the dissociation times so obtained, values for the length parameters that characterize noninteracting model potential curves V_1(r) and V_1(r) for dissociation via both exit channels may also be determined. Early time detection of [Biv•••Bi]•• reflects dynamical behavior over transition-state regions of the potential surfaces and allows various aspects of the nature of the force field governing fragmentation to be deduced. Finally, model quantum and classical calculations of the dissociation process are presented, which reproduce many of the salient features of the observed reaction dynamics

Femtosecond selective control of wave packet population

Femtosecond selective control of wave packet population is reported for molecular iodine. It is shown that both population and phase control of the packet motion can be observed by a 2-D pulse sequence of variable delay times and phase angles. Extension to other type of control experiments is also discussed

Femtosecond selective control of wave packet population

Femtosecond selective control of wave packet population is reported for molecular iodine. It is shown that both population and phase control of the packet motion can be observed by a 2-D pulse sequence of variable delay times and phase angles. Extension to other type of control experiments is also discussed

Femtosecond Real-Time Probing of Reactions. 6. A Joint Experimental and Theoretical Study of 8I_2 Dissociation

The dynamics of the ultraviolet photofragmentation of bismuth dimer are studied experimentally and theoretically in the time domain. Employing the technique of femtosecond transition-state spectroscopy, the evolution of the dissociative process along two reaction channels leading to the 6p^3(^4S^0_(3/2) + 6p^3(^2D^0_(3/2) and 6p^3(^4S^0_(3/2)) + 6p^3(^D^0_(5/2)) levels of the atomic products is investigated following initial excitation of Bi_2 at λ. = 308 nm. The broad spectral width of the ultrashort probe laser pulse coupled with the closely spaced excited energy levels of Bi enables fluorescence via some 14 atomic transitions to be monitored in real time, rendering possible the detection of dissociating molecules at different internuclear separations on the controlling potential surfaces. Long-time detection of the ^2D^0_(3/2) spin-orbit level permits clocking of the reaction along the lower energy exit channel, for which we report a dissociation time τ_(1/2) of approximately 1 ps, at which time the product Bi atoms are separated by some 10.7 Å. Analogous measurements for the reaction giving rise to the higher-lying J = 5/2 level of the ^2D_j term yield a value of τ_(1/2) = 1.5 ps, corresponding to an interfragment distance of 7.5 Å. From the dissociation times so obtained, values for the length parameters that characterize noninteracting model potential curves V_1(r) and V_1(r) for dissociation via both exit channels may also be determined. Early time detection of [Biv•••Bi]•• reflects dynamical behavior over transition-state regions of the potential surfaces and allows various aspects of the nature of the force field governing fragmentation to be deduced. Finally, model quantum and classical calculations of the dissociation process are presented, which reproduce many of the salient features of the observed reaction dynamics