Ultracold Cesium Research Articles

Vib-rotational spectrum of ultracold cesium molecule 0g- long range state

In this paper, high-resolution vib-rotational spectrum of ultracold cesium molecule in its first excited state of 6S1/2+6P3/2 with dissociation limit 0g- long range state is obtained by cold atom fluorescence frequency modulation method. The rotation constants of different vibration energy levels of cesium molecule for vibrational quantum number from 0 to 51 are achieved. The results are in good agreement with the theoretical results given by Daniel.

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.

Measurement of Energy Level Shift of Ultracold Cesium Atoms by Raman Pump–Probe Spectroscopy

AC Stark shift and Zeeman shift of ultracold atoms are measured by a simple Raman pump–probe spectroscopy. We systematically investigate the relationship between these energy level shifts and the experimental parameters of trapping beam intensity, trapping beam detuning and magnetic gradient. The experimental results agree with theoretical values predicted by F ¼ 1 $ F 0 ¼ 2 model, which is developed from a multi-level cesium atom interacting

Direct measurement of laser-induced frequency shift rate of ultracold cesium molecules by analyzing losses of trapped atoms

We report on a quantitative experimental determination of the laser-induced frequency shift rate of the ultracold cesium molecules formed via photoassociation (PA) by means of the trap loss measurement of the losses of trapped atoms in a standard magneto-optical trap. The experiment was directly performed by varying the photoassociation laser intensity without any additional frequency monitor technologies. Our experimental method utilized dependences of the losses on the laser-induced frequency shift rate based on the conditions of the identified photoassociation spectral shape. We demonstrated that the method is sensitive enough to determine small frequency shifts of rovibrational levels of ultracold cesium molecules.

Improvement of signal-to-noise ratio of the Cs2 photoassociation spectroscopy by using dark SPOT magneto-optical trap

In this paper, a high sensitive photoassociation spectroscopy of cesium molecular 0g- long-range state close to the 6S1/2+6P3/2 dissociation limit is reported based on modulated ultracold cesium atoms in a dark-spot magneto-optical trap. The atoms are mainly populated in hyperfine level F=3 which is called dark hyperfine state, where atoms are not interacting with trapping light and not influenced by interatomic force. We employed lock-in detection technique by modulating fluorescence of cold atoms to obtain high sensitivity spectroscopy. The signal-to-noise ratio of spectroscopy in dark SPOT is up to 115.6, which is remarkably improved. Our technical proved to be a robust tool for effectively improving the signal-to-noise ratio of atom loss spectroscopy.

Experimental study of rovibrational spectrum of ultracold polar RbCs molecules

Ultracold polar RbCs molecules are produced via photoassociation in a dual dark-SPOT magneto-optical trap, in which ultracold rubidium and cesium atoms with high densities are formed by laser cooling and trapping. The a3∑+ triplet metastable state ultracold RbCs molecules with 104/s production rate are detected using resonance-enhanced two-photon ionization. The ultra-high resolution rovibrational spectra of (2)0+, (3)0- and (2)0- rovibrational states are observed by scanning the photoassociation laser frequency. The rotational constants of (2)0+, (3)0- and (2)0- vibrational states are 0.00349 cm-1, 0.00649 cm-1 and 0.00372 cm-1 by fitting respectively.

Enhancing photoassociation efficiency by using a picosecond laser pulse with cubic-phase modulation

The photoassociation (PA) dynamics of ultracold cesium atoms steered by the picosecond laser pulse with cubic-phase modulation has been investigated theoretically by solving numerically the time-dependent Schr\"odinger equation using the mapped Fourier grid method. The temporal duration of the pulse is prolonged, and the pulse area is enlarged by modulating the cubic phase. The PA efficiency is related to the pulse area. When the pulse area is larger than a certain value, the cubic-phase pulses noticeably enhance the PA efficiency, although they have lower energies.

Cold cesium molecules produced directly in a magneto—optical trap

We report on the observation of ultracold ground electric-state cesium molecules produced directly in a magneto—optical trap with a good signal-to-noise ratio. These molecules arise from the photoassociation of magneto—optical trap lasers and they are detected by resonantly enhanced multiphoton ionization technology. The production rate of ultracold cesium molecules is up to 4×104 s−1. We measure the characteristic time of the ground electric-state cesium molecules generated in the experiment and investigate the Cs2+ molecular ion intensity as a function of the trapping laser intensity and the ionization pulse laser energy. We conclude that the production of cold cesium molecules may be enhanced by using appropriate experimental parameters, which is useful for future experiments involving the production and trapping of ultracold ground electric-state molecules.

Photoassociation dynamics driven by a modulated two-color laser field

Photoassociation (PA) dynamics of ultracold cesium atoms steered by a modulated two-color laser field $\phantom{\rule{4pt}{0ex}}E(t)={E}_{0}f(t)\mathrm{cos}(\frac{2\ensuremath{\pi}}{{T}_{p}}\ensuremath{-}\ensuremath{\varphi})\mathrm{cos}({\ensuremath{\omega}}_{L}t)$ is investigated theoretically by numerically solving the time-dependent Schr\odinger equation. The PA dynamics is sensitive to the phase of envelope (POE) $\ensuremath{\varphi}$ and the period of the envelope ${T}_{p}$, which indicates that it can be controlled by varying POE $\ensuremath{\varphi}$ and period ${T}_{p}$. Moreover, we introduce the time- and frequency-resolved spectrum to illustrate how the POE $\ensuremath{\varphi}$ and the period ${T}_{p}$ influence the intensity distribution of the modulated laser pulse and hence change the time-dependent population distribution of photoassociated molecules. When the Gaussian envelope contains a few oscillations, the PA efficiency is also dependent on POE $\ensuremath{\varphi}$. The modulated two-color laser field is available in the current experiment based on laser mode-lock technology.

Excitation Dynamics of Ultracold Cesium nS Rydberg Atoms

Ultracold cesium n S ( n =60–70) Rydberg atoms are prepared using the two-photon scheme in a magneto-optical trap (MOT). The number of resonant Rydberg atoms is measured by the pulsed field ionization technique, and the dependences of the Rydberg signal on excitation duration and external DC electric field are investigated. The excitation dynamics and blockade effects due to long-range interactions are obtained. The effect of external electric field on Rydberg excitation is also investigated, and the experimental result shows an enhanced blockade with a weak external electric field.

Efimov Resonances in Ultracold Quantum Gases

Ultracold atomic gases have developed into prime systems for experimental studies of Efimov three-body physics and related few-body phenomena, which occur in the universal regime of resonant interactions. In the last few years, many important breakthroughs have been achieved, confirming basic predictions of universal few-body theory and deepening our understanding of such systems. We review the basic ideas along with the fast experimental developments of the field, focussing on ultracold cesium gases as a well-investigated model system. Triatomic Efimov resonances, atom-dimer Efimov resonances, and related four-body resonances are discussed as central observables. We also present some new observations of such resonances, supporting and complementing the set of available data.

Universality of the Three-Body Parameter for Efimov States in Ultracold Cesium

We report on the observation of triatomic Efimov resonances in an ultracold gas of cesium atoms. Exploiting the wide tunability of interactions resulting from three broad Feshbach resonances in the same spin channel, we measure magnetic-field dependent three-body recombination loss. The positions of the loss resonances yield corresponding values for the three-body parameter, which in universal few-body physics is required to describe three-body phenomena and, in particular, to fix the spectrum of Efimov states. Our observations show a robust universal behavior with a three-body parameter that stays essentially constant.

High sensitive determination of laser-induced frequency shifts of ultracold cesium molecules

We experimentally present a technique for sensitively determining the laser-induced frequency shifts of the long-range molecular vibrational and rotational levels. The scheme relies on an optical frequency shifter, leading to two laser beams with a precise and adjustable frequency interval. A series of photoassociation spectra are recorded with both beams inducing molecular lines, whose peak separation provides an accurate frequency ruler to measure the frequency shifts of cesium molecular levels, which have not yet been observed in previous reports. The data are compared to theoretical predictions and show a good agreement.

Inelastic collisions of ultracold polar LiCs molecules with caesium atoms in an optical dipole trap

We investigate collisions of ultracold polar LiCs molecules and ultracold caesium atoms. LiCs molecules are formed in an optical dipole trap by photoassociation of caesium and lithium atoms via the B(1)Π excited state followed by spontaneous emission to the X(1)Σ(+) ground state and the lowest triplet state a(3)Σ(+). The molecules are then stored together with caesium atoms in the same optical trap. Rate coefficients for the loss of molecules induced by collisions with surrounding Cs atoms are measured for molecular ensembles produced via different photoassociation resonances. The results are analyzed in terms of the unitarity limit for the inelastic rates and predictions from the universal model of Idziaszek and Julienne (Phys. Rev. Lett., 2010, 104, 113202).

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.

Slow Mass Transport and Statistical Evolution of an Atomic Gas across the Superfluid–Mott-Insulator Transition

We study transport dynamics of ultracold cesium atoms in a two-dimensional optical lattice across the superfluid-Mott-insulator transition based on in situ imaging. Inducing the phase transition with a lattice ramping routine expected to be locally adiabatic, we observe a global mass redistribution which requires a very long time to equilibrate, more than 100 times longer than the microscopic time scales for on-site interaction and tunneling. When the sample enters the Mott-insulator regime, mass transport significantly slows down. By employing fast recombination loss pulses to analyze the occupancy distribution, we observe similarly slow-evolving dynamics, and a lower effective temperature at the center of the sample.

Research on improve the SNR of ultracold cesium molecule rovibronic spectrum via best optimization parameter control

Ultracold atom photoassociation spectroscopy is significant for studying the long-range molecular potential energy structure. The signal-noise ratio of ultracold Cesium Molecule photoassociation Rovibronic Spectrum is one of the indicators as a measure of detection technology which directly affect the distinguishing ability and detection sensitivity of the spectra. We obtain an long-range ultracold cesium molecular hyperfine rovibration spectra by modulating the fluorescence spectroscopy. We find that demodulation parameters have a significant impact to the signal-noise ratio of spectra by studying the demodulation parameters such as integration time and sensitivity, which show nonlinear relation with the ratio. We achieve the optimal control of the signal-noise ratio for spectrum according to our experiment, which laid an important foundation for further studying the long-range state rovibration level of ultracold cesium molecule.

Experimental investigation of Stark effect of ultra-cold 39D cesium Rydberg atoms

In this paper, we investigate the Stark effect of ultra-cold 39D cesium Rydberg atoms in low-field. The Stark structure of 39D Rydberg states is calculated numerically. The cold cesium atoms are excited to Rydberg states via two-step process and the Stark spectra are obtained by field-ionization method. The scalar and tenson polarizabilities of 39D cesium Rydberg atoms are measured to be α5/22=62(7) MHz·V-2cm2，α5/20=－146(13) MHz·V-2cm2, α3/22=73(6) MHz·V-2cm2，α3/20=－106(20) MHz·V-2cm2 respectively. The experimental values are in agreement with the theoretical results.

Lifetime measurement of ultracold caesium Rydberg states

We measure the nS and nD (n = 30–40) state lifetimes of caesium Rydberg atoms in a conventional magneto-optical trap using the field ionization technique, which is consistent with the existing theoretical model through suppressing collisions and super-radiance effects. We also investigate variation of the lifetimes with densities of Rydberg atoms by changing the pulse energy of the dye laser. The results indicate that collisions and super-radiance effects have a large influence on the accuracy of lifetime measurement at high densities of Rydberg atoms.

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.