Zhang Lin-Jie

Measurement of quantum defects of nS and nD states using field ionization spectroscopy in ultracold cesium atoms

This paper reports that ultracold atoms are populated into different nS and nD Rydberg states (n = 25~52) by two-photon excitation. The ionization spectrum of an ultracold Rydberg atom is acquired in a cesium magneto-optical trap by using the method of pulse field ionization. This denotes nS and nD states in the ionization spectrum and fits the data of energy levels of different Rydberg states to obtain quantum defects of nS and nD states.

Experimental Research of Spontaneous Evolution from Ultracold Rydberg Atoms to Plasma

The spontaneous evolution from ultracold Rydberg atoms to plasma is investigated in a caesium MOT by using the method of field ionization. The plasma transferred from atoms in different Rydberg states (n = 22-32) are obtained experimentally. Dependence of the threshold time of evolving to plasma and the threshold number of initial Rydberg atoms on the principal quantum number of initial Rydberg states is studied. The experimental results are in agreement with hot-cold Rydberg?Rydberg atom collision ionization theory.

Electric dipole moments of lithium atoms in Rydberg states

Recently, the diverse properties of Rydberg atoms, which probably arise from its large electric dipole moment (EDM), have been explored. In this paper, we report electric dipole moments along with Stark energies and charge densities of lithium Rydberg states in the presence of electric fields, calculated by matrix diagonalization. Huge electric dipole moments are discovered. In order to check the validity of the EDMs, we also use these electric dipole moments to calculate the Stark energies by numerical integration. The results agree with those calculated by matrix diagonalization.

Numerically Calculated Stark Structures of Cesium Rydberg Atom and Experimental Observation in an Ultracold Gas

The Stark structure of the cesium atom is calculated using parametric model potential, up-to-date quantum defects, and the same phase convention as that of conventional hydrogen. Using this phase convention makes the phase comparison between other atoms and the hydrogen atom more convenient. Experimental works are performed in an ultracold gas. The calculated Stark structures of the cesium atom for n =19 and 50D are in good agreement with our experimental results. The calculated transition probabilities for the Stark states near the n =19 are in good agreement with our observed spectra. The polarizabilities of the 50D components are measured and discussed in detail.

Spatial distribution measurement of the microwave electric field strength via the Autler-Townes effect of Rydberg atom

We demonstrate the high-resolution spatial feature measurement of microwave electric field using an cesium atomic vapor cell based on the electromagnetically induced transparency (EIT) spectrum of 133Cs Rydberg atom. The microwave electric field with the frequency of 6.95 GHz couples the transition of 47D5/2→48P3/2 Rydberg states. The EIT spectrum of a 6S1/2-6P3/2-47D5/2 ladder system will split by the Autler-Townes(AT) effect under the microwave electric field. The dependence of AT splitting separation on the microwave electric fields strength is observed. Moreover, we present the imaging of the spatial feature of microwave electric field in the atomic vapor cell. The theoretical maximum spatial resolution is about λMw/430.

Quantum based RF E-field sensing by using two-photon transition in Rydberg atoms

It has been proved that quantum coherence effects in highly-excited Rydberg atoms could provide a revolutionary solution for RF field measurement. A two-photon transition due to interaction of RF electric field with cesium Rydberg atoms will be discussed. RF E-field whose carrier frequency satisfies a two-photon transition can induce an Autler-Townes splitting within electromagnetically induced transparency (EIT) spectroscopy, and the field strength is directly linked to the measured energy splitting and Plancks constant. Proof-of-concept measurement results will be presented, which also indicate the possibility of sub-wavelength sensing. This work is of major significance for developing quantum-based RF field metrology.

High-l Rydberg States' Interference Using a Double-Pulse Electric Field

The interference behavior of high-l Rydberg states is investigated in external fields. We prepare high-l states from an initial excited ns Cs Rydberg state by applying one electric-field pulse. The interference between the initial ns state and the high-l states is investigated by two time-delayed short electric-field pulses. The state selective field ionization technique is used to measure the transfer ratio versus the field pulses parameters. The visibility of interference is defined to describe interference and the results show that a relative long duration of electric-field pulse will weaken the interference.

Stark spectra of Rydberg states in atomic cesium in the vicinity of n = 18

The Stark structures in a cesium atom around n = 18 are numerically calculated. The results show that the components of 20D states with a small azimuthal quantum number |m| shift upward a lot, and those with a large |m| shift downward a little within 1100 V/cm. All components of P states shift downward. Experimental work has been performed in ultracold atomic cesium. Atoms initially in 6P3/2 state are excited to high-n Rydberg states by a polarization light perpendicular to the field, and Stark spectra with |m| = 1/2, 3/2, 5/2 are simultaneously observed with a large linewidth for the first time. The observed spectra are analyzed in detail. The relative transition probability is calculated. The experimental results are in good agreement with our numerical computation.

Ionization Detection of Ultracold Ground State Cesium Molecules

Photoassociation of ultracold atoms is an important method for producing stable ultracold molecules with extensive applications. Ion spectroscopy technique, which has higher sensitivity compared with trap loss spectroscopy and fragment spectroscopy, plays an important pole in the research of photoassociation spectroscopy. Based on ion spectroscopy technique, a complete experimental system is employed to produce and detect the ultracold ground state molecules, including the equipment of photoionization and time-of-fight mass spectroscopy. Ultra-cold ground state cesium molecules are demonstrated by the ionization detection technique. The number of the ground-state molecules produced in our MOT is measured. In addition, the relationship of the time interval of the cesium atom ion and the cesium molecular ion to the metal grid voltage is studied for the optimization of the experimental parameters.

Recombination during expansion of ultracold plasma

Signals of ultracold plasma are observed by two-photon ionization of laser-cooled caesium atoms in a magneto-optical trap. Recombination of ions and electrons into Rydberg atoms during the expansion of ultracold plasma is investigated by using state-selective field ionization spectroscopy. The dependences of recombination on initial electron temperature (1–70 K) and initial ion density (~1010 cm−3) are investigated. The measured dependence on initial ion density is N1.547+0.004 at a delay time of 5 μs. The recombination rate rapidly declines as initial electron temperature increases when delay time is increased. The distributions of Rydberg atoms on different values of principal quantum number n, i.e. n = 30–60, at an initial electron temperature of 3.3 K are also investigated. The main experimental results are approximately explained by the three-body recombination theory.