Engineering and Control of High n Rydberg Wavepackets

Classical, semiclassical, and quantum dynamical methods will be employed to develop protocols for engineering "designer" wave packets in high-n Rydberg states. They are the prototypical laboratory for exploring the classical- to-quantum crossover, for the formation of atomic states of mesoscopic dimension, and for non-linear dynamics. Rydberg wave packets can be designed, shaped and controlled with remarkable precision. This opens up novel opportunities to explore wave packet dynamics with unusual spatio-temporal characteristics. High-n Rydberg states can be manipulated by electronic field pulses, in particular sequences of half-cycle pulses, as well as microwave radiation. Within this project, genetic algorithms and optimal control concepts will be implemented to theoretically develop protocols for excitation and manipulation of designed wave packets and to study their coherent evolution and their decoherent collapse. They include creation of designer wave packets of unprecedented high n quantum number and size creation of counter-propagating wave packets within a single atom and the first realization of the intraatomic Aharonov-Bohm interferences creation of the, so far, elusive "planetary atoms" of high double Rydberg excitation formation of high Rydberg pair excitation and Rydberg many-body states to study time dependent Rydberg- Rydberg interactions and dipole blockade.

Wavepackets formed by the superposition of very highly excited atomic states, called Rydberg wavepackets, are of great conceptual interest for quantum physics. They provide a link between the quantum and the classical worlds and form a laboratory for testing fundamental notions such as properties of ultrafast electronic dynamics, dephasing and decoherence. The Rydberg atoms are giants in the microscopic world of atoms reaching sizes of almost macroscopic dimensions. Together with the experimentalists from Rice University, we have theoretically developed and explored protocols to create Rydberg wavepackets that allow probing fundamental notions of quantum physics. One highlight was the creation of the Bohr atom almost 100 years after its conception: a well localized electron revolving around the nucleus on a circular orbit. Dispersion and dephasing of such a wavepacket could be successfully suppressed by application of synchronized external electric fields drawing on analogies of planetary motion (Trojan asteroids). This way the classical orbital motion could be sustained for thousands of revolutions. This breakthrough just in time for the centennial celebration fo Niels Bohrs atomic model in 2013 received considerable media attention (among others in Nature 498 p22). Equally important as a stepping stone for further design and control of electronic motion was the realization of atoms with gigantic dipole moments (of the order of 100,000 Debye). Atoms near the ground state are generically round, the electric charge cloud is spherically distributed around the nucleus. For high Rydberg states of both alkali and alkali-earth atoms we could develop excitation protocols to create highly polarized states when the outer electron is displaced from the nucleus by tens of thousands of Ångstroms. Similarly strongly polarized wavepackets have been also investigated in fullerenes and shake-up states of helium. Furthermore, as one of the important applications of such large dipole moments we could demonstrate the dipole blockade process for very high n Rydberg atoms for which the blockade radius reaches macroscopic dimensions.