Integrated Calendar

The hybridization of the rotational states of an anisotropic molecule by a far-off-resonant optical field imparts angular momentum to the molecule or removes it, which alters the centrifugal term in the molecule’s electronic potential and hence pushes its vibrational and rotational manifolds upward or downward. The angular momentum imparted by the field may suffice to expel the highest vibrational level from the molecular potential. Our numerical simulations applied to the Rb2 and KRb Feshbach molecules indicate for feasible laser pulses that this can be used to accurately recover the square of the vibrational wave function of the expelled state and, by inversion, also the long-range part of the molecular potential.

A combination with a weak electrostatic field can convert second-order alignment by the optical field into a strong first-order orientation that projects up to 90% of the body-fixed dipole moment of a polar molecule on the static field direction. This is the basis of a versatile orientation technique which found applications ranging from molecule optics and spectroscopy to chemistry and surface science. Recent work on OCS molecules has shown how to keep the interaction with the combined fields adiabatic and thereby make the best of the technique.

The electric dipole-dipole interaction between a pair of polar molecules undergoes an all-out transformation when superimposed by a far-off resonant optical field. The combined interaction potential becomes tunable by variation of wavelength, polarization and intensity of the optical field and its dependence on the intermolecular separation exhibits a crossover from an inverse-power to an oscillating behavior.
The ability thereby offered to control molecular interactions opens up avenues toward the creation and manipulation of novel phases of ultracold polar gases among whose characteristics is a long-range entanglement of the dipoles' mutual orientation.

How do we make sense of sensory inputs? One important clue may be the central role of selective and predictive attention, by focusing limited resources on behaviorally relevant sensory channels and modulating information flow at multiple stages, to improve perception.Our approach is to study the effect of attention on information processing at the single neuron level in the primary auditory cortex (A1) of animals trained on multiple auditory tasks that require selective attention to task-specific salient spectral frequency or temporal cues. Our results demonstrate that when animals actively attend to a task, their auditory cortical neurons can rapidly change their spectrotemporal filter characteristics to improve the animal’s performance. Thus, cortical sensory filters are not fixed, but are highly adaptive, and show dynamic, task-specific transformations during auditory behavior. To study the broader neural circuits involved in attention, we have initiated research on several other components in the network, including secondary auditory cortical areas, nucleus basalis, and the prefrontal cortex (PFC), a brain area known to play a key role in attention and decision-making. In contrast to A1, PFC responses are largely independent of the acoustic properties of sound, and encode an abstract, categorical representation of sound meaning. Recent studies show that electrical stimulation of PFC can elicit receptive field transformations in A1 neurons very similar to the attentional effects observed during behavior. Our working model suggests a top-down instructive role for PFC, and emphasizes the importance of interactions between multiple brain areas during selective attention that lead to matched auditory cortical filters for attended acoustic stimuli, creating a dynamic, evolving neural representation of task-salient sounds and thus optimizing perception on a moment-to-moment basis.

We want to make a “non-biological” system which can self-replicate. The idea is to design particles with specific and reversible and irreversible interactions, introduce seed motifs, and cycle the system in such a way that a copy is made. Repeating the cycle would double the number of offspring in each generation leading to exponential growth. Using the chemistry of DNA either on colloids or on DNA tiles makes the specific recognition part easy. In the case of DNA tiles we have in fact replicated the seed at least to the third generation. The DNA linkers can also be self-protected so that particles don’t interact unless they are held together for sufficient time – a nano-contact glue, and we have discovered a new type of topological interaction associated with concatenation of DNA loops which gives a Velcro-like binding. Chemical modification of the DNA allows us to permanently crosslink hybridized strands for irreversible bonds and a new type of photolithography. We have designed and produced colloidal particles that use novel “lock and key” geometries to get specific and reversible physical interactions. We have also investigated the limits of distinct specific interactions that we can DNA encode on a single particle, how 'polygamous' it can be made, and find that it is entropically and combinatorially restricted to ~100 mates.