X. Y. Xu

Photon-induced tunneling in optomechanical systems

In contrast to recent studies [Rabl, Phys. Rev. Lett. 107, 063601 (2011); Nunnenkamp et al., Phys. Rev. Lett. 107, 063602 (2011)] on photon blockade that prevents subsequent photons from resonantly entering the cavity in optomechanical systems, we study the photon-induced tunneling that increases the probability of admitting subsequent photons in those systems. In particular, we analytically and numerically show how two- or three-photon tunneling can occur by avoiding single-photon blockade. Our study provides another way on photon control using a single mechanical resonator in optomechanical systems.

Antibunching photons in a cavity coupled to an optomechanical system

We study the photon statistics of a cavity linearly coupled to an optomechanical system via second-order correlation functions. Our calculations show that the cavity can exhibit strong photon antibunching even when optomechanical interaction in the optomechanical system is weak. The cooperation between the weak optomechanical interaction and the destructive interference between different paths for two-photon excitation leads to the efficient antibunching effect. Compared with the standard optomechanical system, the coupling between a cavity and an optomechanical system provides a method to relax the constraints to obtain a single photon by optomechanical interaction.

The study of autoionizing states of lutetium atoms by resonance ionization spectroscopy

The authors describe the investigation of the autoionizing states of lutetium atoms by exciting the states 2D3/2o, 2D5/2o, 4D3/2o and 4D5/2o with tunable dye lasers by means of a resonance ionization time-of-flight mass spectrometer. Twenty eight autoionizing transitions were measured and 12 autoionizing states were found. Their Shore-Fano profile parameters were determined by a nonlinear fitting program. The ionization probability for different schemes and some ionization cross sections were compared. On the basis of this, the authors have given the optimal schemes of lutetium atom photoionization through autoionizing states. In addition, the relation between ion signal and the laser pulse energy was discussed.

Rydberg and autoionizing states of neutral ytterbium

In the study of Yb atomic Rydberg states, new members of 6sns 1S0 series for n=23, 24, 66-116 and 6snd 1D2 series for n=81-114 were observed. The data are in excellent agreement with the MQDT analysing results. The autoionizing Rydberg series 6p12 /ns ( 1/2 , 1/2 )10 were investigated by three-step laser excitation. The ICE model was used to explain the experimental spectrum, and it has been proved to be suitable for describing the excitation of the autoionizing Rydberg states with a weakly-excited core.

Study on ionic Rydberg states of calcium

Using five-laser resonance excitation, we observe the p Rydberg series with n from 39 to 92. The energy levels calculated using the self-consistent-field method and quantum defect theory are in good agreement with the experimental results.

Observation of the highly excited states of Lanthanum

The highly excited states of Lanthanum are studied by means of laser resonance ionization time-of-flight spectrometer. Based on the two-step laser resonance excitation with intermediate state 5d2(3F)6p 2D5/20, three new Rydberg state (RS) series (5d2(a3F2)ns, 5d2(a3F3)nd and 5d2(a1D2)ns) and a number of autoionizing states (AIS) are obtained. Theoretical calculation leads the quantum defects of ns and nd series to the value δs=4.35 and δd=2.80 respectively, which are very close to the experimental results. The Rydberg state series 5d2(a3F2)ns gives the first ionization limit to be 44979.8±0.3 cm−1, which is an order more accurate than ever.

Constant-electric-field ionization mass spectroscopy in laser-excited Yb + Rydberg states

Using a new method of constant-electric-field ionization of Rydberg states of ions, we have eliminated the influence of the direct multiphoton ionization background in multistep excitation of Yb+ Rydberg states and obtained the pure spectrum of np(n = 17−86) Rydberg levels of Yb+.The precision of the value of the Yb ii ionization potential has been greatly improved to 98 231.75(20) cm−1.

Rydberg energy levels and their structure in the ruthenium atom

The Rydberg energy levels and their structure in the Ru atom for the 4d7(4F)ns (n=28-50) and 4d7(4F)nd (n=24-56) series were measured by means of the laser resonance excitation-electric field ionization method. The Rydberg energy levels and relevant quantum defects are calculated using the relativistic self-consistent-field method. The calculated quantum defect values for the s and d series are: mu s=3.5, mu d=1.9. The relative line strengths within the multiplet of an electron configuration are also calculated. All the theoretical results are consistent with the experiments and the spectral terms of the measured lines can be identified. This is the first work to measure and analyse the level structure of Rydberg states of a platinum group atom. The first ionization potential of Ru is obtained by a non-linear fitting program as 59 365.9 (4) cm-1. This result is a significant improvement over that obtained by Callender et al. (1985).

Study of highly excited states of Yb

We report here the first study of the Yb double‐Rydberg states based on a new time‐of‐flight mass spectroscopy system with five‐lasers resonance excitation. The first quantitative measurement of relative excitation strength for various core states was worked out. The atomic Rydberg states, the autoionizing Rydberg states and ionic Rydberg states were also investigated.

Study on ionic Rydberg states of lanthanum

Using five-laser resonance excitation via the intermediate state 5d6d 1P1, the La+ Rydberg states with n from 23 to 62 have been measured. Based on the eigenchannel quantum defects µα and transformation matrices Uiα, which are calculated from first principles by relativistic multichannel theory, the energy levels of the La+ Rydberg series are calculated within the framework of multichannel quantum defect theory and are in good agreement with the experimental values. With the calculated results we provide clear assignments for the experimental spectra.