Optimal preparation of Bose and Fermi atomic gas mixtures of ^(87)Rb and ^(40)K in a crossed optical dipole trap

We report on the optimal production of the Bose and Fermi mixtures with ^(87) Rb and ^(40)K in a crossed optical dipole trap(ODT).We measure the atomic number and lifetime of the mixtures in combination of the spin state |F=9/2,m_F=9/2) of^(40)K and |1,1>of ^(87) Rb in the ODT,which is larger and longer compared with the combination of the spin state 19/2,9/2) of^(40)K and 12,2) of ^(87)Rb in the ODT.We observe the atomic numbers of ^(87)Rb and ^(40)K shown in each stage of the sympathetic cooling process while gradually reducing the depth of the optical trap.By optimizing the relative loading time of atomic mixtures in the MOT,we obtain the large atomic number of ^(40)K(~6 ×10^(6)) or the mixtures of atoms with an equal number(~1.6 × 10^(6)) at the end of evaporative cooling in the ODT.We experimentally investigate the evaporative cooling in an enlarged volume of the ODT via adding a third laser beam to the crossed ODT and found that more atoms(8 × 10^(6)) and higher degeneracy(T/T_(F)=0.25) of Fermi gases are obtained.The ultracold atomic gas mixtures pave the way to explore phenomena such as few-body collisions and the Bose-Fermi Hubbard model,as well as for creating ground-state molecules of ^(87)Rb^(40)K.

Efficient loading of cesium atoms in a magnetic levitated dimple trap

We report a detailed study of magnetically levitated loading of ultracold ^(133)Cs atoms in a dimple trap.The atomic sample was produced in a combined red-detuned optical dipole trap and dimple trap formed by two small waist beams crossing a horizontal plane.The magnetic levitation for the ^(133)Cs atoms forms an effective potential for a large number of atoms in a high spatial density.Dependence of the number of atoms loaded and trapped in the dimple trap on the magnetic field gradient and bias field is in good agreement with the theoretical analysis.This method has been widely used to obtain the Bose–Einstein condensation atoms for many atomic species.

Review of chip-scale atomic clocks based on coherent population trapping

Research on chip-scale atomic clocks （CSACs） based on coherent population trapping （CPT） is reviewed. The back- ground and the inspiration for the research are described, including the important schemes proposed to improve the CPT signal quality, the selection of atoms and buffer gases, and the development of micro-cell fabrication. With regard to the re- liability, stability, and service life of the CSACs, the research regarding the sensitivity of the CPT resonance to temperature and laser power changes is also reviewed, as well as the CPT resonance＇s collision and light of frequency shifts. The first generation CSACs have already been developed but its characters are still far from our expectations. Our conclusion is that miniaturization and power reduction are the most important aspects calling for further research.

Ramsey-coherent population trapping Cs atomic clock based on lin‖lin optical pumping with dispersion detection

A Cs vapor cell-based atomic clock that uses a lin‖lin pumping scheme with dispersion detection is reported. This atomic clock shows potential for high performance because of its high contrast pumping scheme, and for miniaturization because of its simple architecture. The experimental setup and optimal operating parameters for the clock are introduced.The current fractional frequency stability is measured to be 1.3 × 10^-12/■ up to 20s and reaches 3.1 × 10^-13 at 200 s. We have thoroughly investigated the related noise sources that affect clock frequency stability at the 1s and 100s levels. The investigation shows that the laser frequency noise limits the clock frequency stability significantly. The clock performance can be further improved by technically upgrading the laser frequency stabilization setup.

High contrast atomic magnetometer based on coherent population trapping

We present an experimental and theoretical investigation of the coherent population trapping （CPT） resonance excited on the D1 line of 87Rb atoms by bichromatic linearly polarized laser light. The experimental results show that a lin｜｜lin tran- sition scheme is a promising alternative to the conventional circular-circular transition scheme for an atomic magnetometer. Compared with the circular light transition scheme, linear light accounts for high-contrast transmission resonances, which makes this excitation scheme promising for high-sensitivity magnetometers. We also use linear light and circular light to detect changes of a standard magnetic field, separately.

Atomic magnetometer with microfabricated vapor cells based on coherent population trapping

An atomic magnetometer based on coherent population trapping(CPT) resonances in microfabricated vapor cells is demonstrated. Fabricated by the micro-electro-mechanical-system(MEMS) technology, the cells are filled with Rb and Ne at a controlled pressure. An experimental apparatus is built for characterizing properties of microfabricated vapor cells via the CPT effects. The typical CPT linewidth is measured to be about 3 k Hz(1.46 k Hz with approximately zero laser intensity) for the rubidium D1 line at about 90℃. The effects of pressure, temperature and laser intensity on CPT linewidth are studied experimentally. A closed-loop atomic magnetometer is finally finished with a sensitivity of 210.5 p T/Hz1/2 at 1 Hz bandwidth. This work paves the way for developing an integrated chip-scale atomic magnetometer in the future.

Experiments on trapping ytterbium atoms in optical lattices

Experiments on trapping ytterbium atoms in various optical lattices are presented. After the two-stage cooling, first in a blue magneto-optical trap and then in a green magneto-optical trap, the ultracold 171 Yb atoms are successfully loaded into one-, two-, and three-dimensional optical lattices operating at the Stark-free wavelength, respectively. The temperature, number, and lifetime of cold 171 Yb atoms in one-dimensional lattice are measured. After optimization, the one-dimensional lattice with cold 171Yb atoms is used for developing an ytterbium optical clock.

High-performance coherent population trapping clock based on laser-cooled atoms

We present a coherent population trapping clock system based on laser-cooled^(87)Rb atoms.The clock consists of a frequency-stabilized CPT interrogation laser and a cooling laser as well as a compact magneto-optical trap,a highperformance microwave synthesizer,and a signal detection system.The resonance signal in the continuous wave regime exhibits an absorption contrast of~50%.In the Ramsey interrogation method,the linewidth of the central fringe is31.25 Hz.The system achieves fractional frequency stability of 2.4×10^(-11)/(√τ),which goes down to 1.8×10^(-13)at 20000 s.The results validate that cold atom interrogation can improve the long-term frequency stability of coherent population trapping clocks and holds the potential for developing compact/miniature cold atoms clocks.

Interference properties of a trapped atom interferometer in two asymmetric optical dipole traps

We investigate interference properties of a trapped atom interferometer where two symmetric optical dipole traps(ODTs)act as the atomic wave-packets splitter and combiner with internal state labelling.After the preparation of initial superposition states,the atomic wave-packet is adiabatically split and moves into two spatially separate asymmetric ODTs.The atomic wave-packets in two ODTs are then adiabatically recombined after a duration of free evolving in traps,completing the interference cycle of this atom interferometer.We show that the interferogram exhibits a series of periodic revivals in interference visibility.Furthermore,the revival period decreases as the asymmetry of two dipole potentials increases.By introducing an echo sequence to the interferometer,we show that while the echo effect is not influenced by the asymmetry of the two ODTs,the onset of periodic revivals changes by the echo sequence.Our study provides an effective method to cancel or compensate the phase shift caused by position and time correlated force.

Trapping and Cooling of Single Atoms in an Optical Microcavity by a Magic-Wavelength Dipole Trap

We present trapping and cooling of single cesium atoms inside a microcavity by means of an intracavity far-off- resonance trap （FORT）. By the ＇magic＇ wavelength FORT, we achieve state-insensitive single-atom trapping and cooling in a microeavity. The cavity transmission of the probe beam strongly coupled to single atoms enables us to continuously observe the intracavity atom trapping. The average atomic localization time inside the bright FORT is about 7ms by introducing cavity cooling with appropriate detuning. This experiment presents great potential in coherent state manipulation for strongly coupled atom photon systems in the context of cavity quantum electrodynamics.

Single layer atom chip for magnetically trapping one-dimensional array of ultracold atoms

We propose a wire configuration to create a one-dimensional （1D） array of magnetic microtraps for trapping ultracold atoms. The configuration is formed by replacing the central part of the Z-wire pattern with a zigzag wire. We simulate the performance of this pattern by the finite element method which can take both the width and depth of the wire into consideration. The result of simulation shows that this configuration can create magnetic microtraps which can be separated and combined by changing bias magnetic field. We manage to split Z-wire trap and prove that similar result can occur for the new wire configuration. The fabrication processes of the atom chip are also introduced. Finally we discuss the loading method.

Coupled Two-Dimensional Atomic Oscillation in an Anharmonic Trap

In atomic dynamics, oscillation Mong different axes can be studied separately in the harmonic trap. When the trap is not harmonic, motion in different directions may couple together. In this work, we observe a two- dimensional oscillation by exciting atoms in one direction, where the atoms are transferred to an anharmonic region. Theoretical calculations are coincident to the experimental results. These oscillations in two dimensions not only can be used to measure trap parameters but also have potential applications in atomic interferometry and precise measurements.

Single atoms transferring between a magneto-optical trap and a far-off-resonance optical dipole trap

Based on our work on single cesium atoms trapped in a large-magnetic-gradient vapour-cell magneto-optical trap （MOT）, the signal-to-noise ratio （SNR） is remarkably improved. Also a far-off-resonance optical dipole trap （FORT） formed by a strongly-focused 1064 nm single frequency Nd：YVO4 laser beam is introduced. One cesium atom is prepared in the MOT, and then it can transfer successfully between the MOT and the FORT which is overlapped with the MOT. Utilizing the effective transfer, the lifetime of single atoms trapped in the FORT is measured to be 6.9± 0.3 s. Thus we provide a system where the atomic qubit can be coherently manipulated.

Observation of single neutral atoms in a large-magnetic-gradient vapour-cell magneto-optical trap

Single caesium atoms in a large-magnetic-gradient vapour-cell magneto-optical trap have been identified. The trapping of individual atoms is marked by the steps in fluorescence signal corresponding to the capture or loss of single atoms. The typical magnetic gradient is about 29 mT/cm, which evidently reduces the capture rate of magneto-optical trap.

Loss of cold atoms due to collisions with residual gases in free flight in a magneto-optical trap

The loss rate of cold atoms in a trap due to residual gas collisions differs from that in a free state after the cold atoms are released from the trap. In this paper, the loss rate in a cold rubidium-87 atom cloud was measured in a magneto-optical trap （MOT） and during its free flight. The residual gas pressure was analyzed by a residual gas analyzer, and the pressure distribution in a vacuum chamber was numerically calculated by the angular coefficient method. The decay factor, which describes the decay behavior of cold atoms due to residual gas collisions during a free flight, was calculated. It was found that the decay factor agrees well with theoretical predictions under various vacuum conditions.

Enhanced cold mercury atom production with two-dimensional magneto-optical trap

A cold atom source is important for quantum metrology and precision measurement.To reduce the quantum projection noise limit in optical lattice clock,one can increase the number of cold atoms and reduce the dead time by enhancing the loading rate.In this work,we realize an enhanced cold mercury atom source based on a two-dimensional(2D)magnetooptical trap(MOT).The vacuum system is composed of two titanium chambers connected with a differential pumping tube.Two stable cooling laser systems are adopted for the 2D-MOT and the three-dimensional(3D)-MOT,respectively.Using an optimized 2D-MOT and push beam,about 1.3×10^(6)atoms,which are almost an order of magnitude higher than using a pure 3D-MOT,are loaded into the 3D-MOT for202Hg atoms.This enhanced cold mercury atom source is helpful in increasing the frequency stability of a neutral mercury lattice clock.

Continuously transferring cold atoms in caesium double magneto-optical trap

We have established a caesium double magneto-optical trap （MOT） system for cavity-QED experiment, and demonstrated the continuous transfer of cold caesium atoms from the vapour-cell MOT with a pressure of - 1 × 10^-6 Pa to the ultra-high-vacuum （UHV） MOT with a pressure of - 8 × 10^-8 Pa via a focused continuous-wave transfer laser beam. The effect of frequency detuning as well as the intensity of the transfer beam is systematically investigated, which makes the transverse cooling adequate before the atoms leak out of the vapour-cell MOT to reduce divergence of the cold atomic beam. The typical cold atomic flux got from vapour-cell MOT is - 2 × 10^7 atoms/s. About 5 × 10^6 caesium atoms are recaptured in the UHV MOT.

Dependence of the ^(85)Rb coherent population trapping resonance characteristic on the pressure of N_2 buffer gas

In order to exploit its potential applications, we experimentally study the dependence of ^85 Rb-based coherent population trapping （CPTi resonance on N2 buffer gas with 6 vapor cells filled with natural rubidium and N2. The experiments are carried out at different pressures and temperatures, and the results reveal that higher cell temperature makes the resonance more sensitive to N2 pressure. Thus, it is importmlt to choose a proper buffer gas pressure at a given cell temperature. This work provides valuable data for the application of 85Rb CPT resonance with a buffer gas of N2.

A Single Folded Beam Magneto-Optical Trap System for Neutral Mercury Atoms

Mercury is a promising candidate for the optical lattice clock, due to its low sensitivity to the blackbody radiation. We develop a single folded beam magneto-optical trap for the neutral mercury optical lattice clock, with a 253. 7nm frequency quadrupled laser. Up to 1.7 × 10^6 （202Hg） or 1.5 × 10^6 （199Hg） atoms can be captured, and the atom temperature is lowered to 170μK （202Hg） or 50μK （199Hg）. The cold atom signals of all six rich abundant isotopes are observed in this system.