Manipulation Of Ultracold Rydberg Atom By External Electric Field

Rydberg atom, outermost electrons excited to high-n (principal quantum number) states (n>>1), shows novel properties, such as strong interaction (n4), long lifetime (n3), huge polarizability (n7). Rydberg atoms have raised attentions in many fields such as quantum logic gates, single-photon sources and many-body systems with strong long-range interactions due to blockade effect, the Rydberg-excitation inhibition of neighboring atoms.About ?107 cesium atoms are trapped in the magneto-optical trap with ?100?K and density ?109 cm-3 by laser cooling and trapping technique. Rydberg atoms are prepared by two-step excitation and detected by pulse field ionization technique. Two grids in the two sides of atom sample are used to apply external fields to manipulate the Rydberg atoms.Due to small fractional quantum defect, energy of nS Rydberg state is close to (n-4) hydrogenic states. The avoided crossing between them can be formed in small electric field. The Stark spectra are precisely measured and the avoided crossings between nS Rydberg state and (n-A) hydrogenic states are investigated in detail. Base on this, a new method to refine the nS quantum defect is proposed by comparing the measured avoided crossing with theoretical ones. A highly dipolar Rydberg atom gas is prepared by adiabatically manipulating nS Rydberg state through an avoided crossing to high-/ Rydberg stark states. Additionally, a new controllable Rydberg-atom interferometer is demonstrated by precisely scanning the initial Rydberg state through one avoided crossing twice. Details are as following:1. The ion spectra of cesium three-level avoided crossings between nS state and high-l Rydberg states in the n-4 manifold in the Stark spectrum are precisely measured. A new method for the determination of specific quantum defects of highly excited nS Rydberg states is proposed through experimental measurements of the energy gaps between the levels of a three-level avoided crossing, at its center, in combination with corresponding quantum simulations.2. The highly dipolar Rydberg atom gas with strongly interaction in an electric field is prepared by adiabatically scanning the field amplitude through selected avoided crossing. The initial prepared nS Rydberg state with dipole moment ?500 Debye is adiabatically populated to high-l Stark states and thus obtains large permanent electric dipole moments ?2500 Debye. The adiabatically transformed atoms are embedded in a background of other high-|m| Stark states. These conditions are conducive to selective m-mixing of the adiabatically transformed atoms, making adiabatic passage experimentally detectable.3. Through manipulation of the passage process, a special Rydberg-atom interferometer was demonstrated by an external electric field ramped twice through selected avoided crossing. The avoided crossing is viewed as the "splitter" and "combiner" in the traditional interferometer. The center of avoided crossing produces the superposition between two initial states. The interferometric signal is observed by varying the hold time between the field ramps. The coherence frequencies observed in the Fourier transforms of the signal reflect the energy-level differences in the underlying Stark map. Due to the limitation of transition selection rules (?l=±1), it cannot directly excite the intermediate state (P state) to high-l Stark state. This interferometer overcomes this limitation and provides a new method to measure the Stark spectrum.The innovations of this work:1. A new method to refine the quantum defect of highly excited Rydberg states is demonstrated by comparing the energy gaps (?100MHz) between evolved levels of selected avoided crossing in Stark map. This is immune to uncertainty of ionization threshold as the traditional way.2. Preparation and detection of highly dipolar Rydberg atoms realized by the manipulating the passage through the avoided crossing. This method only needs very small electric field (?1V/cm) to realize huge tuning of dipole moments (?2500 Debye) from initial nS Rydberg state (-500 Debye).3. A new Rydberg-atom interferometer is demonstrated through manipulating the electric field forth and back through a selected avoided crossing. The method allows us to map out levels that, due to selection rules, are hidden in optical excitation spectra.