Rydberg atoms, which have a highly excited outer electron, are easily manipulated by electric fields. Using a magneto-optical trap, we cool Rubidium atoms to a few hundred millionths of a Kelvin above absolute zero and then excite to Rydberg states. Our first project looks at the dipole-dipole interactions of two atoms starting in the 33p state and ending in the 34s and 33s states. The standard technique is to apply an increasing electric field that ionizes the Rydberg electron and sends it to a detector, but unfortunately the signals overlap. A genetic algorithm is used to separate the signals by controlling the ionization pathway. In order to understand how a Rydberg atom ionizes we need to build a model. The current model, which uses a semi-empirical formula, neglects important quantum phase information. In our second project we are building a computational model that includes continuum states along with discrete states. We present progress on a new model which takes into account the differences in normalization for continuum and discrete states.
Rydberg atoms, which have a highly excited outer electron, are easily manipulated by electric fields. Using a magneto-optical trap, we cool Rubidium atoms to a few hundred millionths of a Kelvin above absolute zero and then excite to Rydberg states. Our first project looks at the dipole-dipole interactions of two atoms starting in the 33p state and ending in the 34s and 33s states. The standard technique is to apply an increasing electric field that ionizes the Rydberg electron and sends it to a detector, but unfortunately the signals overlap. A genetic algorithm is used to separate the signals by controlling the ionization pathway. In order to understand how a Rydberg atom ionizes we need to build a model. The current model, which uses a semi-empirical formula, neglects important quantum phase information. In our second project we are building a computational model that includes continuum states along with discrete states. We present progress on a new model which takes into account the differences in normalization for continuum and discrete states.
The electron signals from the field ionization of two closely spaced Rydberg states of rubidium-85 are separated using quantum control. In selective field ionization, the state distribution of a collection of Rydberg atoms is measured by ionizing the atoms with a ramped electric field. Generally, atoms in higher energy states ionize at lower fields, so ionized electrons which are detected earlier in time can be correlated with higher energy Rydberg states. However, the resolution of this technique is limited by the Stark effect. As the electric field is increased, the electron encounters numerous avoided Stark level crossings which split the amplitude among many states, thus broadening the time-resolved ionization signal. Previously, a genetic algorithm has been used to control the signal shape of a single Rydberg state. The present work extends this technique to separate the signals from the 34s and 33p states of rubidium-85, which are overlapped when using a simple field ramp as in selective field ionization.
Summary form only given. Interactions between neutral atoms are generally weak, but exciting these atoms in a Rydberg state considerably enhances their interaction through a long-range dipole-dipole potential. An interesting application of this dipole-dipole interaction is the dipole blockade in Rydberg excitation. This effect offers exciting possibilities for manipulating quantum bits stored in a single collective excitations in mesoscopic ensembles, or for realizing scalable quantum logic gate. The dipole blockade effect has been demonstrated in atomic ensembles by different groups, and recently also with two independently trapped atoms, which shows the possibility of creating entangle states and quantum logic gates. To extend and continue these results with more atoms, a promising method is to use atoms trapped in an optical lattice in the Mott insulator phase. To excite atoms into a Rydberg state, and to control the interactions and the dipole blockade, a high resolution laser scheme is needed. We use a two-photon excitation scheme 5s1/2rarr 6p3/2rarr ns or nd. The first step, at 420 nm, is realized by doubling a MOPA laser, with the second step at ~ 1000 nm. Both lasers are locked to a Fabry-Perot cavity, and the total excitation bandwidth is less than 3 MHz. After the excitation into the Rydberg state, we apply a pulsed electric field to ionize and detect the Rydberg atoms with an ion detector. To characterize and improve the efficiency of our ion detection, we have explored the direct ionization of ultracold atoms in a magneto-optical trap, or in a Bose-Einstein condensate. This calibration will allows us to characterize precisely the Rydberg excitation and to monitor its time evolution. First results on the Rydberg excitation of ultracold atoms in dipole traps and optical lattices will be presented. The prospect for creating Rydberg excitations inside a Mott insulator will also be discussed.
We study a hitherto unexplored regime of the Rydberg excitation blockade using highly Stark-shifted, yet long-living, states of Rb atoms subject to electric fields above the classical ionization limit. Such states allow tuning the dipole-dipole interaction strength while their ionization rate can be changed over 2 orders of magnitude by small variations of the electric field. We demonstrate laser excitation of the interacting Rydberg states followed by their detection using controlled ionization and magnified imaging with high spatial and temporal resolution. Our work reveals new possibilities to engineer the interaction strength and dynamically control the ionization and detection of Rydberg atoms, which can be useful for realizing and assessing quantum simulators that vary in space and time.
Rydberg atoms, i.e. atoms with one or more highly excited electrons, show exaggerated properties compared to ground state atoms. For example, their energy levels are very sensitive to external electric fields (Stark effect) and they exhibit strong interatomic interactions, which can lead to a suppression of excitation known as the Rydberg blockade. The latter property makes Rydberg atoms promising candidates for quantum simulation and quantum computing. This work describes the direct observation of the excitation blockade for highly Stark-shifted Rydberg atoms induced by controllable dipole-dipole interactions. We investigate the electric field region around and above the classical ionization threshold, which is typically not considered suitable for blockade experiments. We excite Rydberg atoms in the energy region corresponding to the unperturbed 43S1/2 state at electric fields around 127V/cm out of a magneto-optically trapped cloud of 87Rb atoms with a temperature of 150 μK. We tune the dipole-dipole interaction by the applied electric field thus changing the electric dipole moment of the excited state. The position of the Rydberg atoms is detected by ionization and subsequent ion imaging; the controlled ionization of the atoms is achieved by adiabatic transfer of the Rydberg state to an ionizing state. For the spatially resolved detection of the atoms, a high resolution ion microscope for cold atoms has been developed and experimentally characterized. It features a maximum magnification of 1000 and sub-micrometer spatial resolution. A theoretical treatment of highly Stark-shifted Rydberg states is developed introducing a complex absorbing potential. It is capable of predicting the ionization rates of the Rydberg states for a wide range of electric fields and energies with only one free parameter. Together with the numerical calculations, measurements of the ionization spectra for different Rydberg states are presented. The 43S1/2 state is measured in an electric-field range from 125V/cm to 165V/cm (classical ionization limit 127V/cm), the 70S1/2 state in an electric-field range from 15V/cm to 35V/cm (classical ionization limit 16.1V/cm) and the 100S1/2 state in an electric-field range from 7V/cm to 19V/cm (classical ionization limit 3.7V/cm). Our results show an intricate energy level structure with broad, strongly ionizing states as well as sharp, nearly non-ionizing states. The numerical calculations are also used for the prediction of selective field ionization spectra and the results are used to identify Förster resonances in the Stark spectrum of the 45D5/2 state. Complementary to the spatially resolved measurements in high electric fields, the Rydberg blockade effect is also observed via the excitation number statistics at Förster resonances.
A Rydberg atom has a highly excited valence electron which is weakly bound and far from the nucleus. These atoms have exaggerated properties that make them attractive candidates for quantum computation and studies of fundamental quantum mechanics. A widely used method for measuring the energy level of the outer electron is to ionize it with an electric field pulse and send it to a detector where the resulting spectrum is measured. However, this technique fails to resolve energy levels that are closely spaced. The electron’s path to ionization branches several hundreds of times, causing neighboring energy levels to overlap. By using an engineered electric field pulse, we can manipulate which branches the electron follows. To design our electric field pulse, we created a genetic algorithm. A genetic algorithm is an optimization process analogous to biological evolution. Our algorithm creates a random population of electric field pulses, evaluates the fitness of the field pulses, and allows the fittest members of the population to mate and create a new generation. We present results of our simulations.
Collisions involving Rydberg atoms reveal detailed information on the state of a background medium and can be used as diagnostic probes of temperature and density distributions in a neutral or ionized gas. Spectroscopy of Rydberg atoms in highly excited states reveals the interaction of the Rydberg electron with core electrons, including relativistic effects, and can be used for precise determination of fundamental constants. The advent of ultracold trapping and cooling methods in the last three decades has ushered in a new paradigm in Rydberg physics control and manipulation. The concept of the Rydberg blockade, for instance, al- lows for precise control of long-range dipolar interaction between atoms, creation of correlated many-body wave functions, and realization of macroscopic quantum entanglement and quan- tum logic operations. The formation of a new class of Rydberg molecules arising from ground and Rydberg atom collisions can be used to manipulate electron-atom scattering phase shifts, form and manipulate molecules with enormous permanent electric dipole moments, study Ry- dberg chemistry at the ultracold, and realize macroscopic quantum polaronic systems. In this thesis, I will investigate charge transfer from covalent ground-Rydberg collisions to form heavy ion pair states. In another related study, I explore the formation of spin-mixed ultralong range Rydberg molecules, by accounting for spin-dependent relativistic fine and hyperfine interac- tion. Such studies help to not only explain experimental observations, but also point to how molecular reactions can be controlled using small electric or magnetic fields.