Jieying Wang

Velocity-selective spectroscopy measurements of Rydberg fine structure states in a hot vapor cell

A velocity-selective spectroscopy technique for studying the spectra from hot Rydberg gases is presented. This method provides high-resolution measurement of the spectrum interval. Based on this method, the velocity-selective hyperfine splitting of intermediate states is measured, as well as the Doppler-free fine-structure splitting of the Rydberg states via two-photon Rydberg excitation in a room-temperature 133Cs vapor cell. The experiment data and theoretical predictions show excellent agreement.

Realization of a watt-level narrow-linewidth 318-nm UV laser and single-photon Rydberg excitation of cesium atoms (Conference Presentation)

Nowadays the long-range dipole-dipole interaction between highly-excited Rydberg atoms at micrometer distance become promising way to establish the atom-atom quantum entanglement and to implement the two-qubit logic gate. For alkali metal atoms, single-photon excitation from the ground state to the desired Rydberg state demands powerful narrow-linewidth ultra-violet (UV) laser, which is very challenging. Maybe just because of this, the studies of single-photon Rydberg excitation of alkali metal atoms are rare. Alternatively people have employed the two-photon or three-photon Rydberg excitation scheme. However, comparing with the single-photon Rydberg excitation, the two-photon or three-photon scheme has following drawbacks: atomic decoherence due to the photon scattering from the lower and upper transitions, and light shift of the involved ground state and Rydberg state due to the lower and upper transition laser beams. Thanks to the efficient laser frequency conversion technology with PPXX material and the well-developed commercial fiber laser as well as fiber amplifier, we have implemented a tunable 318.6-nm UV laser system based on the cavity-enhanced second-harmonic generation following the single-pass sum-frequency generation of 1560.5-nm and 1076.9-nm fiber-amplified lasers. More than 2-Watt output of the 318.6-nm UV laser has been achieved with a typical linewidth of smaller than 10 kHz. Employing the UV laser system we have demonstrated a single-photon Rydberg excitation spectroscopy of cesium (Cs) atoms. Partial Cs atoms can be directly excited from 6S_1/2 ground state to nP_3/2 (n = 70 - 100) Rydberg states, and Rydberg excitation spectra are obtained with transmission enhancement of a probe beam locked to Cs 6S_1/2 (F = 4) - 6P_3/2 (F’ = 5) cycling transition because partial population on the ground state (F = 4) are transferred to Rydberg state. The quantum defect for Cs nP_3/2 (n = 70 -100) Rydberg states is determined experimentally. Further more, the demodulated single-photon Rydberg excitation spectrum is employed to stabilize the UV laser to specific Cs Rydberg transition to improve the laser frequency stability. References: [1] Opt. Express 25 (2017) p.22510; [2] J. Opt. 19 (2017) 045501; [3] J. Opt. Soc. Am. B 33 (2016) p.2020; [4] Opt. Commun. 370 (2016) p.150. Funding: the National Natural Science Foundation of China (61475091).

Large-scale continuous-variable dual-rail cluster entangled state based on spatial mode comb

In recent continuous-variable (CV) multipartite entanglement researches, the number of fully inseparable light modes has been increased dramatically by the introduction of a multiplexing scheme in either the time domain or the frequency domain. In this paper, we propose a scheme that a large-scale (≥ 20) CV dual-rail cluster entangled state is established based on a spatial mode comb in a self-imaging optical parametric oscillator, which is pumped by two spatial Laguerre-Gaussian modes with different polarization and identical frequency. A sufficient condition of full inseparability for a CV dual-rail cluster entangled state is used to evaluate the degree of quantum entanglement. It is shown that entanglement exists over a wide range of analyzing frequency and pump parameter. We have found a new scheme that uses the optical parametric cavity to generate a large-scale entanglement based on optical spatial mode comb. The presented system will be hopefully as a practical entangled source for quantum information.

Nearly deterministic loading of a single cesium atom in a magneto-optical trap and in a microscopic optical tweezer by feedback control

Based on feedback control techniques and our realization of nearly complete transferring cold cesium (Cs) atoms from a magneto-optical trap (MOT) to a far-off-resonance microscopic optical tweezer, we investigated the possibility for nearly deterministic loading of a single Cs atom in a MOT and in a microscopic optical tweezer. We combined feedback controls on the gradient of the MOT quadrupole magnetic field (QMF) and on blue-detuned light-assisted collisions (LAC) of confined cold atoms in the tweezer. Using active feedback on QMF of the MOT, we have achieved ~ 98% of probability of single atom loading in a MOT. In a microscopic optical tweezer, by combining the feedback controls on the QMF and the LAC, we finally achieved ~ 95.2% of probability of single atom loading in the tweezer. This two-path feedback control scheme may be extended to load a small-size 2D tweezer array with exact single atom trapped in each site simultaneously. This is very important and promising to implement an addressable multiple-qubit system for demonstrating quantum register and quantum processor.

Optimization of the experimental parameters of cesium CPT system

Based on a Λ-type three-level system consists of cesium (Cs) 6S1/2 (Fg = 3) and 6S1/2 (Fg = 4) long-lived ground states and 6P3/2 (Fe = 4) excited state, we have experimentally measured and theoretically analyzed the characters of coherent population trapping (CPT) resonances in Cs vapor cells with different partial pressure of neon (Ne) as buffer gas around room temperature. The impact of some experimental parameters, such as the relative intensity ratio between two phase-locked laser beams, the laser intensity, with or without buffer gas and the partial pressure of Ne, the temperature and the longitudinal magnetic field, on the CPT resonance was studied in details. With the optimized parameters, we got typical CPT signal with the full-width half-maximum (FWHM) linewidth as narrow as ~ 181 Hz in a Cs vapor cell filled with 30 Torr of Ne as buffer gas.