Collision ionization processes in the optical excitation of Rydberg states of potassium

真司 植松

久人 平石

A. Sharma, G. L. Bhale, M. A. N. Razvi

R. Beigang, Andreas Nebel, Bettina-Maria Becker +1 more

Philip Adamson

This thesis discusses an approach to excite potassium atoms to very highly excited states (Rydberg states), and then tune their energy levels to induce resonant collisions between atoms. Potassium gas is super-cooled to 1 mK and confined to a small volume in a magneto-optical trap. A 405 nm laser diode, electronically locked to a potassium vapor cell via Doppler free spectroscopy, excites these atoms from the 4s1/2 state (ground state) to the 5p3/2 state. A 978 nm laser then excites the 5p3/2 to nd3/2 or nd5/2 transition, creating Rydberg atoms. Since there is no ground state reference for this transition, an alternative method must be used to lock the laser's frequency. A scanning transfer cavity lock transfers the stability of a 632 nm HeNe reference laser to the unstable 978 nm laser diode by passing both lasers through a Fabry-Perot interferometer. Once Rydberg atoms have been created, their energy levels are tuned with an external electric field so that collisions between atoms cause resonant atomic transitions to different Rydberg states. The Rydberg atoms are ionized with a second, stronger electric field, and detected by microchannel plate detectors. Rydberg atoms with different principal quantum numbers ionize at different electric field strengths, so a successful collision signal has multiple peaks from the microchannel plates.

Shuzhen Ye

Very-high-n (n~300) Rydberg atoms serve as a powerful tool to study chaos and quantum optical phenomena. Measurements using a series of alternating impulsive kicks applied to potassium Rydberg atoms reveal that a phase space geometric structure called the turnstile governs the ionization process. Studies of the excitation spectra for potassium Rydberg atoms in a strong sinusoidal electric drive field in the radio frequency (100-300 MHz) regime, display quantum optical phenomena including electromagnetically induced transparency and Aulter-Townes splitting, and the data are well explained within the framework of Floquet theory. In order to study the strong dipole-dipole interactions between neutral atoms, new experimental techniques have been developed to create high densities of very-high-n (n~300-500) strontium Rydberg atoms using two- and three-photon excitation. The data demonstrate that high densities of strongly-polarized quasi-one-dimensional states can be produced and form the basis for further manipulation of the atomic wave functions. The strontium Rydberg states are modeled using a two-active-electron theory which produces results in good agreement with experimental observations.