Compact magneto-optical traps using planar optics

Magneto-optical traps (MOTs) composed of magnetic fields and light fields have been widely utilized to cool andconfine microscopic particles. Practical technology applications require miniaturized MOTs. The advancement of planaroptics has promoted the development of compact MOTs. In this article, we review the development of compact MOTs basedon planar optics. First, we introduce the standardMOTs. We then introduce the gratingMOTs with micron structures, whichhave been used to build cold atomic clocks, cold atomic interferometers, and ultra-cold sources. Further, we introducethe integrated MOTs based on nano-scale metasurfaces. These new compact MOTs greatly reduce volume and powerconsumption, and provide new opportunities for fundamental research and practical applications.

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.

Microwave-mediated magneto-optical trap for polar molecules

Realizing a molecular magneto-optical trap has been a dream for cold molecular physicists for a long time. However,due to the complex energy levels and the small effective Lande g-factor of the excited states, the traditional magneto-optical trap（MOT） scheme does not work very well for polar molecules. One way to overcome this problem is the switching MOT,which requires very fast switching of both the magnetic field and the laser polarizations. Switching laser polarizations is relatively easy, but fast switching of the magnetic field is experimentally challenging. Here we propose an alternative approach, the microwave-mediated MOT, which requires a slight change of the current experimental setup to solve the problem. We calculate the MOT force and compare it with the traditional MOT and the switching MOT scheme. The results show that we can operate a good MOT with this simple setup.

Two-color cesium magneto-optical trap with 6S1/2-6P3/2-7S1/2(852 nm ＋ 1470 nm) ladder-type system

A 1470 nm＋ 852 nm two-color（TC） cesium（Cs） magneto-optical trap（MOT） with a 6S_（1/2）-6P_（3/2）-7S_（1/2） laddertype system is proposed and experimentally investigated. To the best of our knowledge, it is the first report about the 1470 nm ＋ 852 nm Cs TC-MOT. One of the three pairs of the 852 nm cooling and trapping beams（CTBs） in a conventional Cs MOT is replaced with a pair of the 1470 nm CTBs. Thus, the TC-MOT partially employs the optical radiation forces from photon scattering of the 6P_（3∕2）（F＇= 5）-7S_（1∕2）（F＇＇= 4） excited-state transition（1470 nm）. This TC-MOT can cool and trap Cs atoms on both the red-and blue-detuning sides of the twophoton resonance. This work may have applications in cooling and trapping of atoms using inconvenient wavelengths and background-free detection of cold and trapped Cs atoms.

A cold ^(87)Rb atomic beam

We demonstrate an experimental setup for the production of a beam source of cold 87Rb atoms. The atoms are extracted from a trapped cold atomic cloud in an unbalanced three-dimensional magneto-optical trap. Via a radiation pressure difference generated by a specially designed leak tunnel along one trapping laser beam, the atoms are pushed out continuously with low velocities and a high flux. The most-probable velocity in the beam is varied from 9 m/s to 19 m/s by varying the detuning of the trapping laser beams in the magneto-optical trap and the flux can be tuned up to 4× 10^9 s-1 by increasing the intensity of the trapping beams. We also present a simple model for describing the dependence of the beam performance on the magneto optical trap trapping laser intensity and the detuning.

Efficient fluorescence detection of a single neutral atom with low background in a microscopic optical dipole trap

A single cesium atom is trapped in a far-off-resonance optical dipole trap （FORT） from the magneto-optical trap （MOT） and directly imaged by using a charge-coupled device （CCD） camera. The binary single-atom steps and photon anti-bunching are observed by a photon-counting-based HBT system using fluorescence light. The average atom dwelling time in the FORT is about 9 s. To reduce the background noise in the detection procedure we employ a weak probe laser tuned to the D1 line to il- lurninate the single atom from the direction perpendicular to the large-numerical-aperture collimation system. The second or- der degree of coherence g（2）（r）=0.12_＋0.02 is obtained directly from the fluorescence light of the single atom without deducting the background. The background light has been suppressed to 10 counts per 50 ms, which is much lower compared with the reported results. The measured g（2）（r） is in good agreement with theoretical analysis. The system provides a simple and effi- cient method to manipulate and measure single neutral atoms, and opens a way to create an efficient controlled single-photon source.

Optical forces on neutral atoms in the presence of fluctuating laser fields:numerical analysis

Doppler cooling of^(88)Sr atoms is studied in the presence of off-resonant red-detuned fluctuating laser fields.Using a semi-classical approach,we show that the relevant physical quantities in the cooling process,such as optical forces,the damping coefficient,Doppler temperature,and atom number in the trap,are strongly affected by the laser amplitude and phase fluctuations.We find that the Doppler cooling limit is higher than the predicted Doppler theory for non-fluctuating lasers.This implies an additional heating mechanism exists due to the laser fluctuations.Furthermore,our numerical analysis shows that the effect of laser power stability on reducing the number of trapped atoms in a magneto-optical trap is more substantial than the effect of laser linewidth.

原子源的制备与相干性检测

利用不平衡三维磁光阱(3D-MOT)技术,制备了低速、高通量的连续型原子束。通过使一束冷却光沿着光传播方向形成"中空光束",在MOT中形成一对具有不平衡光辐射压力的对射光束,压力将MOT中冷却与陷俘的87 Rb原子云团从"中空光束"通道中推出产生连续出射的原子。形成的原子束具有一定的速度和速度分布,可反映原子束的相干性。对所制备原子束的相干性进行了测量和分析,结果表明,所产生的原子束的最可几速度约为12m/s,纵向速度分布约为3m/s,对应的德布罗意波波长约为0.4nm,带宽为0.1nm。通过光电倍增管(PMT)收集的荧光强度推算得原子束通量为108～109 atoms/s。