Zhao Yan-Ting

Photoassociative Production and Detection of Ultracold Polar RbCs Molecules

We have produced ultracold polar RbCs molecules via photoassociation starting from laser-cooled 85Rb and 133Cs atoms in a dual-species, forced dark magneto-optical trap. The formed electronically excited RbCs* molecules correlated to the Rb(5S1/2) + Cs(6P1/2) dissociation limit are observed by trap loss spectroscopy. Following the decay of these excited RbCs* molecules, the formed ground state molecules are directly ionized by a two-photon single-color pulse dye laser, which is a new ionization mechanism for ground state RbCs molecules and thence detected by time-of-flight mass spectroscopy.

Systematically investigating the polarization gradient cooling in an optical molasses of ultracold cesium atoms

We systematically investigate the dependence of the temperature of cold cesium atoms of polarization gradient cooling (PGC) in optical molasses on experimental parameters, which contain changing modes of cooling laser, PGC interaction time, cooling laser frequency and its intensity. The SR mode of cooling laser, that means the cooling laser frequency is changed with step mode and cooling laser intensity is changed with ramp mode, is found to be the best for PGC comparing with other SS, RS, and RR modes. We introduce a statistical explanation and an exponential decay function to explain the variation of cold atomic temperature on time. The heating effect is observed when the cooling laser intensity is lower than the saturation intensity of cold atoms. After optimization, the lowest temperature of cold cesium atoms is observed to be about 4uK with the number of 2x10^9, a density of 1x10^11/cm^3 and the phase space density of 4.4x10^(-5). The optimization process and analysis of controllable experimental parameters are also meaningful for other cold atomic systems.We systematically investigate the polarization gradient cooling (PGC) process in an optical molasses of ultracold cesium atoms. The SR mode for changing the cooling laser, which means that the cooling laser frequency is stepped to the setting value while its intensity is ramped, is found to be the best for the PGC, compared with other modes studied. We verify that the heating effect of the cold atoms, which appears when the cooling laser intensity is lower than the saturation intensity, arises from insufficient polarization gradient cooling. Finally, an exponential decay function with a statistical explanation is introduced to explain the dependence of the cold atom temperature on the PGC interaction time.

Investigation of ultracold atoms and molecules in a dark magneto-optical trap

In this paper, ultracold atoms and molecules in a dark magneto-optical trap (MOT) are studied via depumping the cesium cold atoms into the dark hyperfine ground state. The collision rate is reduced to 0.45 s−1 and the density of the atoms is increased to 5.6 × 1011 cm−3 when the fractional population of the atoms in the bright hyperfine ground state is as low as 0.15. The vibrational spectra of the ultracold cesium molecules are also studied in a standard MOT and in a dark MOT separately. The experimental results are analyzed by using the perturbative quantum approach.

Precise measurement of the line width of the photoassociation spectra of ultracold molecules by using a frequency shifter

We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation (PA) spectra are recorded with two laser beam induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the PA spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is (34.84 ? 0.22) MHz. By analyzing other broadening mechanisms, a value of (32.02 ? 0.70) MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.

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.

Fast thermometry for trapped atoms using recoil-induced resonance*

We have employed recoil-induced resonance (RIR) with linewidth on the order of 10 kHz to demonstrate the fast thermometry for ultracold atoms. We theoretically calculate the absorption spectrum of RIR which agrees well with the experimental results. The temperature of the ultracold sample derived from the RIR spectrum is T = 84±4.5 μK, which is close to 85 μK that measured by the method of time-of-flight absorption imaging. To exhibit the fast measurement advantage in applying RIR to the ultracold atom thermometry, we study the dependence of ultracold sample temperature on the trapping beam frequency detuning. This method can be applied to determine the translational temperature of molecules in photoassociation dynamics.

Experimental Measurement of the Absolute Frequencies and Hyperfine Coupling Constants of 133Cs Using a Femtosecond Optical Frequency Comb

High resolution two-photon spectrum of the transitions 6S1/2 → 6P3/2 → 8S1/2, 9S1/2 and 6S1/2 → 6P1/2 → 7D3/2 in neutral 133Cs are presented in a room-temperature vapor cell using a femtosecond optical frequency comb. Spectra are obtained by scanning the repetition frequency of the femtosecond optical frequency comb over the two-photon hyperfine structure. The centroid frequency of the 6S1/2 → 8S1/2, 9S1/2, 7D3/2 transitions are 729009798.80(17) MHz, 806761363.96(11) MHz, and 780894762.595(23) MHz, respectively. The hyperfine coupling constants of the corresponding states are also obtained. The results are consistent with the previous measurements.

Photoassociation of ultracold RbCs molecules into the (2)0− state (v = 189, 190) below the 5S1/2 + 6P1/2 dissociation limit

Ultracold polar RbCs molecules are produced via photoassociation in a laser-cooled mixture of 85Rb and 133Cs atoms. The a3Σ+ state molecules which decay from electronically excited (2)0− state RbCs molecules are detected by resonance-enhanced two-photon ionization. The new rovibrational levels (v = 189, 190) in the (2)0− state are also observed, which exist in theory and have not been observed in experiments yet. The corresponding rotational constants are measured by photoassociation spectroscopy, which are consistent with theoretical calculations using a nonrigid rotor model.

High sensitive detection of high-order partial wave scattering in photoassociation of ultracold atoms

We report on the observation of enhanced high-order partial wave scattering from atom-atom interaction via changing the temperature of a magneto-optical trap in the process of photoassociation. The high-order scattering partial wave is directly manifested through the large signal amplitude of the rovibrational resonance levels of trap-loss spectroscopy from photoassociation.

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.