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.

High efficient Raman sideband cooling and strong three-body recombination of atoms

We report a highly efficient three-dimensional degenerated Raman sideband cooling(3D dRSC)that enhances the loading of a magnetically levitated optical dipole trap,and observe the strong atom loss due to the three-body recombination.The 3D dRSC is implemented to obtain 5×10^(7)Cs atoms with the temperature of~480 nK.The cold temperature enables 1.8×10^(7)atoms loaded into a crossed dipole trap with an optimized excessive levitation magnetic gradient.Compared to the loading of atoms from a bare magneto-optical trap or the gray-molasses cooling,there is a significant increase in the number of atoms loaded into the optical dipole trap.We derive for the three-body recombination coefficient of L_(3)=7.73×10^(-25)cm^(6)/s by analyzing the strong atom loss at a large scattering length of 1418 Bohr radius,and discover the transition from the strong three-body loss to the dominant one-body loss.Our result indicates that the lifetime of atoms in the optical dipole trap is finally decided by the one-body loss after the initial strong three-body loss.

Effect of external magnetic field on the shift of resonant frequency in photoassociation of ultracold Cs atoms

We study the influence of external magnetic field on the shift of the resonant frequency in the photoassociation of ultracold Cs atoms, which are captured in a magnetically levitated optical crossed dipole trap. With the increase of the photoassociation laser intensity, the linear variation of the frequency shift is measured by recording the photoassociation spectra of the long-range 0_u^+ state of Cs molecule below the 6S_(1/2)+ 6P_(1/2) dissociation limit at different magnetic fields.The slope of the frequency shift to the intensity of the photoassociation laser exhibits a strong dependence on the external magnetic field. The experimental data is simulated with an analytic theory model, in which a single channel rectangular potential with the tunable well depth is introduced to acquire the influence of the magnetic field on the atomic behavior in the effective range where photoassociation occurs.

Superfluid to Mott-insulator transition in a one-dimensional optical lattice

Bose–Einstein condensates(BEC)of sodium atoms are transferred into one-dimensional(1D)optical lattice potentials,formed by two laser beams with a wavelength of 1064 nm,in a shallow optical trap.The phase coherence of the condensate in the lattice potential is studied by changing the lattice depth.A qualitative change in behavior of the BEC is observed at a lattice depth of~13.7Er,where the quantum gas undergoes a transition from a superfluid state to a state that lacks well-to-well phase coherence.

Spin current in a spinor Bose–Einstein condensate induced by a gradient magnetic field

We develop a research of spin currents in a^(23)Na spinor Bose–Einstein condensate(BEC)by applying a magnetic field gradient.The spin current is successfully induced by the spin-dependent force arising from the magnetic field gradient.The dynamics of the spin components under the magnetic force is investigated.The study is promising to be extended to produce a longer spin-coherence and to enhance the sensitivity of the spin-mixing interferometry in a spinor BEC.

Generation of coherent blue light via bichromatic pumping in cesium vapor

Diode-pumped alkali lasers,possessing high efficiency and narrow linewidth,can provide feasible solutions for wavelength ranges difficult to reach by commercial lasers.In this study,we investigate a generation of coherent blue light(CBL)via four-wave mixing(FWM)-based up-conversion processes in cesium(Cs)vapor.A bichromatic pumping scheme with 852-and 917-nm lasers drives the Cs atoms to the 6D5/2 excited level,followed by cascaded decay of 6D5/2→7 P3/2→6 S1/2,producing 456-nm CBL under phase matching conditions.The fluorescence in multiple bands from blue to near-and far-infrared in the FWM process is demonstrated under different experimental conditions.To optimize the experimental parameters,we investigate the dependence of 456-nm CBL on the vapor temperature,frequency,and intensity of the two pump lasers.A maximum power of 2.94 mW is achieved with pump powers of 430 mW(for 852 nm)and 470 mW(for 917 nm).The corresponding conversion efficiency is 1.5%/W,three-fold higher than those in previous studies.Our results can contribute to fundamental research on atom–photon interactions and quantum metrology.

Laser intensity induced transparency in atom-molecular transition process

We propose a new transparency mechanism,which is based on photoassociation(PA)laser intensity induced transitional frequency shift for ultracold cesium molecules formed in PA scheme.The PA laser intensity is supposed to change before the atom-molecule resonance.Thus,a remarkable transparent effect for PA laser is expected to appear in the vicinity of original resonant transitional line,where the variation of PA laser intensity induces the shift of the excited molecular levels.The mechanism is different from electromagnetically induced transparency effect and interesting for further research on the scattering length for cesium atomic condensate.

Atom-optically synthetic gauge fields for a noninteracting Bose gas

Synthetic gauge fields in synthetic dimensions are now of great interest.This concept provides a convenient manner for exploring topological phases of matter.Here,we report on the first experimental realization of an atom-optically synthetic gauge field based on the synthetic momentum-state lattice of a Bose gas of ^(133)Cs atoms,where magnetically controlled Feshbach resonance is used to tune the interacting lattice into noninteracting regime.Specifically,we engineer a noninteracting one-dimensional lattice into a two-leg ladder with tunable synthetic gauge fields.We observe the flux-dependent populations of atoms and measure the gauge field-induced chiral currents in the two legs.We also show that an inhomogeneous gauge field could control the atomic transport in the ladder.Our results lay the groundwork for using a clean noninteracting synthetic momentum-state lattice to study the gauge field-induced topological physics.

Topological quantum walks:Theory and experiments

Inspired by recent breakthroughs with topological quantum materials,which pave the way to novel,high-efficiency,low-energy magnetoelectric devices[1-3]and fault-tolerant quantum information processing[4],inter alia,topological quantum walks have emerged as an exciting topic in its own right,especially due to the theoretical and experimental simplifications this approach offers[5-14].Motivated by impressive progress in topological quantum walks,we provide a perspective on theoretical studies and experimental investigations of topological quantum walks focusing on current explorations of topological properties arising for single-walker quantum walks.

Wide and fast-frequency tuning for a stabilized diode laser

External-cavity diode laser(ECDL)has important applications in many fundamental and applied researches.Here we report a method to fast and widely tune the frequency of a stabilized ECDL.The beat frequency between the ECDL and a frequency-locked reference laser is identified by the voltagecontrolled oscillator contained in a phase detector,whose output voltage is subtracted from the flexibly controlled PC signal to generate an error signal for stabilizing the ECDL.The output frequency of the stabilized ECDL can be shifted at a short characteristic time of∼150µs within a range of∼620 MHz.The wide and fast-frequency tuning achieved by our method is compared with other previous works.We demonstrated the performance of our method by the efficient sub-Doppler cooling of Cs atoms with the temperature as low as 6µK.