Zhu Xi-Wen

Phase space analysis of the ion cloud in the second stability region of the Paul trap

The method of phase-space dynamics was used to study the spatial distributions and energetic characteristics of the ion cloud in the second stability region of the Paul trap. It was shown that ions have a smaller average volume and higher mean energy for the typical operating points in the second stability region as compared with the first one, and the distribution behaviors vary remarkably with the phase of the confining r.f. field. The optimum operating point (ar, qr) was found to be (−1.30, 1.87) in the second stability region.

Laser isotope enrichment of lithium by magnetic deflection of a polarized atomic beam

The authors have succeeded in demonstrating laser isotope enrichment via magnetic deflection of a polarized atomic beam. By using a single dye laser with the frequency tuned to the two accidentally close transitions of the natural lithium (22S1/2(F=1/2) to 22P3/2 for 6Li and 22S1/2(F=2) to 22P12/(F=1) for 7Li), 6Li and 7Li atoms in a beam were positively and negatively polarized respectively. The 6Li enrichment was achieved via magnetic deflection of the polarized beam through a hexapole magnet which focuses the positively polarized 6Li atoms and defocuses the negatively polarized 7Li atoms. The dependence of 7Li polarization on laser intensity was experimentally examined, and the result was in good agreement with that calculated by rate equations. The abundance ratio of 6Li to 7Li was enhanced from 1 : 12.5 to about 1 : 3.1.

Fluorescence Detection and Buffer Gas Cooling of Trapped Mercury Ions in Paul Trap

Hg ions are confined in a hyperboloid ion trap. With the rf discharge Hg-202 isotope lamp, the fluorescence signal of trapped Hg ions is observed. By means of buffer gas cooling, the ionic temperature is reduced. As a result, the trapping time is increased and the signal-to-noise ratio (SNR) of the fluorescent signal is improved. The temperature of ion cloud is estimated by measuring the space charge shift.

Micro-motion effect of a trapped ultra-cold ion in a standing-wave laser

In the absence of the requirements of the Lamb-Dicke limit and rotating wave approximation, we semi-classically investigate the dynamics of a trapped ultra-cold ion in the standing-wave laser, with the consideration of the time-dependent potential and pseudo-potential of the Paul trap. The specific calculations show that the larger the Lamb-Dicke parameter eta and the Rabi frequency Ohm, the greater the difference between the dynamics in the time-dependent potential and the pseudo-potential.

Stabilizing Chaos in the rf-Driven Josephson Junction

The models of rf-driven Josephson junctions are investigated as the perturbed systems. It is shown that the heteroclinic orbits corrected by perturbations are stable if some relations between the initial constants and system parameters are satisfied, which leads to Melnikov chaos: To stabilize chaos one has to make the control parameters fitting the relations. The result is compared with the previous numerical work and a good agreement is found.

Realization of Quantum Logic Gates in Ion Traps Without Any Requirement on the Lamb-Dicke Parameter

A scheme is presented for realizing quantum logic gate in an ion trap. In the scheme the state of the mth ion is first replicated onto the collective motion. Then a transformation, conditional on the motional state, is performed on the nth ion. Finally the motional state is replicated back onto the mth ion. By this way the quantum logic gate between the mth and the nth ions is realized. The scheme does not put any requirement on the Lamb-Dicke parameter.

Approximate solution to the driven Jaynes-Cummings model with small detunings

The quasienergies and the steady states of a two-level atom coupled to a quantized cavity mode and driven by a classical periodic field are solved in the case that the detunings among the atom, the cavity mode and the field are small. We also constitute two sets of orthonormal wavefunctions based on the steady states we obtained from the system and present a unitary evolution operator. Finally, the specific calculations show that the approximate solution is a useful tool for the further investigation of the properties of the driven Jaynes-Cummings model with small detunings.

Exact Solution of a Many-Level Atom Interacting with a Monochromatic Field Without Rotating Wave Approximation*

In the coherent-state representation, the technique applied to the Jaynes-Cummings (JC) model in the absence of rotating wave approximation (RWA) is extended to the treatment of a many-level atom interacting with a monochromatic field. Some general results are presented.

Exact Solution of Jaynes–Cummings Model Without Rotating Wave Approximation

In coherent-state representation, the Jaynes-Cummings (JC) model in the absence of rotating wave approximation (RWA), i.e., in detuning case, is treated by the solution of some differential equations with constant coefficients and can be exactly solved. This approach can be easily extended to deal with the JC model without RWA in more complicated cases.

Simple Approach to the Solution of a Trapped and Radiated Cold Ion Beyond the Lamb–Dicke Limit*

Trapping ions outside the Lamb–Dicke limit have been proven to be useful for the laser-cooling and quantum computing. Under the supposition of the Rabi frequency much smaller than the Lamb–Dicke parameter, we can use a simple method to analytically solve the system with a single cold ion trapped and radiated beyond the Lamb– Dicke limit, in the absence of the rotating-wave approximation (RWA). Discussion has been made for the limitation of our approach and the comparison of our results with the solutions under the RWA.