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.
Very-high-n (n300) 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 (n300-500) 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.
Dipole-dipole interactions, the strongest, longest-range interactions possible between two neutral atoms, cannot be better manifested anywhere else than in a Rydberg atomic system. Rydberg atoms, having high principal quantum numbers n>>1 and dipole moments that scale as n^2, provide a powerful tool to examine dipole-dipole interactions. Therefore, we have studied the production and production rates of strontium Rydberg atoms created using two-photon excitation and have explored their properties in two distinct experiments. In the first experiment, very-high-n (n~300) Rydberg atoms are produced in a tightly collimated atomic beam allowing spectroscopic studies of their energy levels and their Stark effects. Simulations using a two-active-electron model, developed by our theoretical collaborators, allow detailed analysis of the results and are in remarkable agreement with the experimental results. The high density of Rydberg atoms achieved ~ 5*10^5 cm^(-3), in this experiment will allow studies of strongly interacting Rydberg-Rydberg systems. The second experiment, in which a cold strontium Rydberg gas is excited in a magneto-optic trap, features an imaging technique offering both spatial and temporal resolution. We use this technique to observe and study the evolution of an ultra-cold strontium Rydberg gas which reveals the importance of Rydberg-Rydberg interactions in the early stages of this evolution. Strongly interacting Rydberg gas provides an opportunity to realize a very strongly-correlated ultra-cold plasma.
The response of highly excited potassium Rydberg states with n $\ensuremath{\sim}305$ to a sinusoidal electric drive field in the radio frequency (100--300 MHz) regime is examined by photoexcitation from the 4s ground state using a uv probe beam. The drive field couples many Rydberg levels simultaneously and results in a coherent response that leads to a variety of multiphoton processes. The excitation spectra are analyzed within the framework of Floquet theory and reveal signatures of quantum optical phenomena such as electromagnetically induced transparency and Autler-Townes splitting seen with few-level systems.
The production of high-n, $n\ensuremath{\sim}300$, quasi-one-dimensional (quasi-1D) strontium Rydberg atoms through two-photon excitation of selected extreme Stark states in the presence of a weak dc field is examined using a crossed laser-atom beam geometry. The dipolar polarization of the electron wave function in the product states is probed using two independent techniques. The experimental data are analyzed with a classical trajectory Monte Carlo simulation employing initial ensembles that are obtained with the aid of quantum calculations based on a two-active-electron model. Comparisons between theory and experiment highlight different characteristics of the product quasi-1D states, in particular, their large permanent dipole moments, $\ensuremath{\sim}1.0to1.2{n}^{2}e{a}_{0}$, where e is the electronic charge and a0 is the Bohr radius. Such states can be engineered using pulsed electric fields to create a wide variety of target states.
The production of very-high-n ($n\ensuremath{\sim}300$--500) strontium Rydberg atoms is explored using a crossed-laser-atom-beam geometry. n1S0 and n1D2 states are created by two-photon excitation via the 5s5p1P1 intermediate state using radiation with wavelengths of $\ensuremath{\sim}$461 and $\ensuremath{\sim}$413 nm. Rydberg atom densities as high as $\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{5}$ cm${}^{\ensuremath{-}3}$ have been achieved, sufficient that Rydberg-Rydberg interactions can become important. The isotope shifts in the Rydberg series limits are determined by tuning the 461-nm light to preferentially excite the different strontium isotopes. Photoexcitation in the presence of an applied electric field is examined. The initially quadratic Stark shift of the n1P1 and n1D2 states becomes near-linear at higher fields and the possible use of n1D2 states to create strongly polarized, quasi-one-dimensional electronic states in strontium is discussed. The data are analyzed with the aid of a two-active-electron (TAE) approximation. The two-electron Hamiltonian, within which the Sr2+ core is represented by a semi-empirical potential, is numerically diagonalized allowing the calculation of the energies of high-n Rydberg states and their photoexcitation probabilities.
The efficient production of very-high-n, $n\ensuremath{\sim}300$, quasi-one-dimensional (quasi-1D) strontium Rydberg atoms through three-photon excitation of extreme Stark states in the presence of a weak dc field is demonstrated using a crossed laser-atom beam geometry. Strongly polarized quasi-1D states with large permanent dipole moments $\ensuremath{\sim}1.2{n}^{2}$ a.u. can be created in the beam at densities ($\ensuremath{\sim}{10}^{6}$ cm${}^{\ensuremath{-}3}$) where dipole blockade effects should become important. A further advantage of three-photon excitation is that the product F states are sensitive to the presence of external fields, allowing stray fields to be reduced to very small values. The experimental data are analyzed using quantum calculations based on a two-active-electron model together with classical trajectory Monte Carlo simulations. These allow determination of the atomic dipole moments and confirm that stray fields can be reduced to $\ensuremath{\le}25\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}$V cm${}^{\ensuremath{-}1}$.
This thesis investigates the effects of strong Rydberg-Rydberg interactions in the presence of three-level coherent phenomena such as electromagnetically induced transparency (EIT), Autler-Townes splitting (ATS) and coherent population trapping (CPT). As a result of their remarkable properties, highly excited Rydberg atoms have great potential for applications in diverse areas. The interaction-induced dipole blockade between the Rydberg atoms has been proposed as a fundamental tool in quantum information processing with neutral atoms. Yet, they require an increasing level of understanding and control. A many-body theory is developed for the Rydberg excitation dynamics in various atomic systems with different densities and velocity distributions such as for atoms in a vapour cell, ultracold atoms in magneto-optical and optical dipole traps, or a system of optical lattices or dipole trap arrays. The systems were investigated by solving the optical Bloch equations numerically for a two-photon ladder excitation scheme, taking into consideration various experimentally relevant conditions for the emergence of the effects of Rydberg-Rydberg interactions. The lineshape properties of the EIT/ATS/CPT spectra are observed and reviewed while the physical arguments for how the lineshape properties change as a function of various parameters are provided. To account for the differing atomic distributions in the atomic systems, a many-body model based on Monte-Carlo simulation is developed to describe the optical response of the multiatoms systems to two-photon excitation laser lights in the regimes of EIT, ATS and CPT and strong atomic interactions. The study of the lineshape properties allows one to understand possible ways to detect the emergence of interaction-induced excitation suppression, asymmetry, line shift and excitation "antiblockade" enhancement effects. Besides these, the main result of this study is the demonstration that the linewidth properties of the Rydberg EIT/ATS/CPT spectra can reveal collective many-body behaviour associated with the creation of many-body entangled states. The linewidth properties provide compelling evidence of the creation of collective states by confirming the predicted dependence of the generalised Rabi frequency on the square root of the number of atoms in the mesoscopic ensemble. This study could help to quantify and control the conditions necessary for creating many-body entanglement within atomic ensembles. The thesis also describes the step towards experimentally investigating the response of an atomic system to excitation lasers and studying the excitation dynamics of interacting atoms in such systems. Significant work was done to set up the two-photon excitation system for preparing atoms in high-lying Rydberg states and performing Rydberg-based vapour cell experiments. Qualitative analysis of the Rydberg states transparency features allows to obtain laser parameters such as the laser linewidths and Rabi frequencies that are used in the theoretical model to create the similarity between the experimental and theoretical parameters. Further works were carried out towards realising the building blocks for experimentally investigating the interactions between Rydberg atoms in ultracold atom systems. This is by setting-up a trapping system capable of producing a highly dense ultracold atom ensemble within a magneto-optical trap, cold enough to serve as a reservoir from which the optical dipole trap can be loaded efficiently. The optical dipole trap is designed and set up to achieve a micron-size trapping potential capable of producing a sub-micron sized atomic cloud, with a controllable number of atoms, where a full blockade effect can be achieved and exploited to implement a qubit system for quantum gate operations.