Zhao Jian-Ming

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.

Effect of Background Noise on the Photon Statistics of Triggered Single Molecules

We theoretically derive exact expressions for Mandels Q parameter of the triggered single molecular source, which is inferred from the probabilities PRS(n) using the record of each photon detection event based on Hanbury Brown and Twiss detection. The real triggered source is recognized as an ideal single photon source with a Poissonian statistics background. How to decrease the background and to increase the efficiency are discussed. It is established that the sub-Poissonian statistics formation can be determined by comparing the measured QRS of the real single triggered molecular with QC of the Poissonian source containing the same mean photons. By this method, we also give an efficient way to measure signal-to-background ratios of triggered single photons.

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.

Experimental Observation of Autler?Townes Splitting in Sub-Doppler Selective Reflection Spectroscopy

We present an experimental study of Autler–Townes splitting of non-linear selective reflection spectroscopy in a Λ-type driven three-level system. The sub-Doppler reflection spectroscopy is observed and the Autler–Townes splitting is measured as functions of the different coupling laser intensity and detuning. The coherent drive splits the excited state into two dressed states and an Autler–Townes splitting emerges in the probe reflection. The experimental results are in good agreement with theoretical fit.

Electromagnetically Induced Absorption and Transparency Spectra of Degenerate Two-Level Systems with a Strong Coupling Field in Cs Vapour

The electromagnetically induced absorption and electromagnetically induced transparency spectra of degenerate two-level systems with a strong coupling laser were observed. The frequency detuning and intensity effect of the coupling laser were demonstrated simultaneously. A dispersion-like spectrum can be obtained when the coupling laser is situated at blue-side detuning. The absorption inversion was realized when the coupling laser intensity is small. The coherent resonance has a linewidth much narrower than the natural linewidth of the optical transitions.

Electromagnetically-induced transparency in a multi-V-type system in cesium atomic vapour

Electromagnetically-induced transparency is observed in a three-level multi-V-type system in cesium vapour at room temperature. The absorption property is measured and the hyperfine structures of atomic states can be determined. The results of the experiment agree with the theoretical analysis.

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.

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.

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.