Wang Yi-qiu

Microwave Atomic Clock in the Optical Lattice with Specific Frequency

A scheme for a microwave atomic clock is proposed for Cs or Rb atoms trapped in a blue detuned optical lattice. The ac Stark shift of the clock transition due to a trapping laser is calculated. We analyze it at some specific laser wavelength. Compared with the case of the fountain clock, the cavity related shifts, the collision shift and the Doppler effect are eliminated or suppressed dramatically in an atomic lattice clock. By analyzing various sources of clock uncertainty, a microwave atomic lattice clock with a high accuracy and small volume is feasible.

Alternating Current Zeeman and Stark Interference Effect in Ramsey Separated Oscillating Fields

Analytic expressions have been derived of the alternating current (ac) Zeeman and ac Stark effect in an atomic beam magnetic resonance method using Ramsey separated oscillating fields. An interesting feature which will affect the normal Ramsey pattern is that an interference fringe is superimposed on the dispersion lineshapes of the normal ac Zeeman or ac Stark effect. We point out that this new character of ac Zeeman (ac Stark) effect generally exists in all kinds of Ramsey method, for example, in the optical Ramsey atomic interferometer and atomic beam frequency standard. An important implication is that, particularly in an atomic beam frequency standard using Ramsey method, this effect has an influence on the evaluation of the second-order Doppler frequency shift.

An Empirical Formula for the Measurement of Spatial Coherence of Trapped Bose Gases

An empirical formula, which demonstrates the interference fringe visibility as a function of the slit separation and the temperature of thermal atoms, is obtained by analysing a recent experiment [Bloch et al. Nature 403 (2000) 166] that refers to the spatial correlation function of a trapped Bose gas below the critical temperature. We find that the decay rate of the coherence function for the non-condensed component is about two orders larger than that of the pure condensed component. The changes of the interference fringe visibility versus the falling time for different temperatures and slit separations are also discussed.

A Scheme for Realizing the Continuous Wave Atom Laser

We propose a scheme for realizing the long-term continuous output of an atom laser. In this scheme the cold atoms in several subsidiary Bose-Einstein condensates (BEC) will be coupled one by one in turn into one main BEC which serves for the continuous output of a coherent atomic beam. We discuss the process of the phase unification of the newly entered BEC atoms with the remaining atoms in the main BEC trap. An ideal dynamical equilibrium can be established when the transition rate of the uncondensed atoms transforming into the condensate and the decay rate of coupling output satisfy some conditions. The coupling method from the subsidiary BEC to the main BEC and the time rates of all different processes are considered.

The Weak-Coupling of Bose-Einstein Condensates

The coherent characteristics of four trapped Bose-Einstein condensates (BEC) conjunct one by one in a ring shape which is divided by two far off-resonant lasers, are studied. Four coupled Gross-Pitaevskii equations are used to describe the dynamics of the system. Two kinds of self-trapping effects are discussed in the coupled BECs, and the phase diagrams for different initial conditions and different coupling strengths are discussed. This study can be used to determine interaction parameters between atoms in BEC.

The Study of the Phase of Bose–Einstein Condensate*

We first propose to study the phase of Bose-Einstein condensate in the phase space. The mean value of the phase and the phase fluctuation of Bose-Einstein condensate are considered, and their explicit expressions are given with the Thomas-Fermi approximation. For a finite atom number, we find that the phase of condensate is determined by the oscillation frequency of the harmonic confining potential at certain time. The effects of the atom number and time on the phase of condensate are also discussed for the same kinds of atoms.

A New Pumping-Probing Scheme for the Optically Pumped Cesium Beam Frequency Standard

A new pumping-probing scheme for the optically pumped cesium beam frequency standard has been experimentally tested in our laboratory. The stability of the optically pumped cesium beam frequency standard was measured by comparing its 10 MHz output with an HP5071A commercial cesium atomic clock. The result shows that the frequency stability for the 1 s and 30000 s sample times are 1.2×10-11 and 3.7×10-13, respectively. It was proved that the new pumping scheme works well. PACS: 06. 20. Fn, 42. 62. Eh

Pyramidal-hollow-beam dipole trap for alkali atoms*

We propose a dark gravito-optical dipole trap, for alkali atoms, consisting of a blue-detuned, pyramidal-hollow laser beam propagating upward and the gravity field. When cold atoms from a magneto-optical trap are loaded into the pyramidal-hollow beam and bounce inside the pyramidal-hollow beam, they experience efficient Sisyphus cooling and geometric cooling induced by the pyramidal-hollow beam and the weak repumping beam propagating downward. Our study shows that an ultracold and dense atomic sample with an equilibrium 3D momentum of � 3 ¯ and an atomic density above the point of Bose-Einstein condensation may be obtained in this pure optical trap. PACC: 3280P; 3380P; 4250

Gealas laser diode pumped cesium beam frequency standard

A laser diode pumped cesium beam frequency standard had been built. The laser diode used for both optical pumping and detection is frequency-locked at the 4-4 transition of Cs D2 line. The voltage controlled crystal oscillator (VCCO) frequency is locked to the center of the Ramsey pattern of the microwave clock transition after frequency multiplying and synthesizing. The preliminary measurement of the frequency stabilities shows that the results are in agreement with the theory, and better results could be achieved by further improving the frequency stability of the laser diode.

Observation of F = 2 Spinor Bose–Einstein Condensation in a Magnetic Field

Multiple-component Bose-Einstein condensation has been observed in a magnetic field generated by a controllable magnetic quadrupole-Ioffe-configuration trap. Different distributions of atoms in spinor Bose–Einstein condensates are created by changing the time difference of switching-off current in quadrupole-Ioffe-configuration coils and bias coils of the magnetic trap. A simple analysis is carried out to explain some phenomena of the experiment.