Zhan Ming-Sheng

Measurement of Local Gravity via a Cold Atom Interferometer

We demonstrate a precision measurement of local gravity acceleration g in Wuhan by a compact cold atom interferometer. The atom interferometer is in vertical Mach-Zehnder configuration realized using a pi/2-pi-pi/2 Raman pulse sequence. Cold atoms were prepared in a magneto-optical trap, launched upward to form an atom fountain, and then coherently manipulated to interfere by stimulated Raman transition. Population signal vs Raman laser phase was recorded as interference fringes, and the local gravity was deduced from the interference signal. We have obtained a resolution of 7 x 10(-9) g after an integration time of 236 s under the best vibrational environment conditions. The absolute g value was derived from the chirp rate with a difference of 1.5 x 10(-7) g compared to the gravity reference value. The tidal phenomenon was observed by continuously monitoring the local gravity over 123 h.

Quantum wavefunctions and fluctuations of mesoscopic RLC circuit

The quantum wavefunctions and the corresponding energy levels of a RLC (Resistance-Inductance-Capacity) electric circuit are obtained by using canonical quantization method and unitary transformation from the classical equation of motion. The quantum fluctuations of charge and current in an arbitrary eigenstate of the system have also been given as well as the uncertainty relation. It is showed that even if at 0 K charge and current in the circuit exhibit quantum fluctuations, which originates from fluctuations of zero point vibrations of the system.

Magic Wavelength of an Optical Clock Transition of Barium

Similar to most of the other alkaline earth elements, barium atoms can be candidates for optical clocks, thus the magic wavelength for an optical lattice is important for the clock transition. We calculate the magic wavelength of a possible clock transition between 6s(2) (1) S(0) and 6s5d (3) D(2) states of barium atoms. Our theoretical result shows that there are three magic wavelengths 615.9 nm, 641.2nm and 678.8nm for a linearly polarized optical lattice laser for barium.

Squeezing via coupling of Bose–Einstein condensates in a double-well potential with a cavity light field

Squeezing via the interaction between the cavity light field and the Bose–Einstein Condensate (BEC) in a double-well potential is considered within the context of the two-mode approximation. For the cavity light field initially in a coherent state, it is shown that by choosing appropriate parameters, quadrature squeezing of the cavity light field can be achieved and it exhibits periodic oscillation. We also study the case in which BEC is tuned to resonance by periodically modulating the trapping potential, and the quadrature squeezing of the cavity field exhibits periodic collapse and revival effect. Both analytic and numerical calculations are performed, and they are found to be in good agreement with each other. The result shows that the quantum statistical properties of the cavity light field can be manipulated by its coupling with the condensates in the double-well potential. On the other hand, dynamical properties of the condensates in the double-well potential will be reflected by the quadrature squeezing of the light field.

Demonstration of a Sagnac-Type Cold Atom Interferometer with Stimulated Raman Transitions

Cold-matter-wave Sagnac interferometers possess many advantages over their thermal atomic beam counterparts when they are used as precise inertial sensors. We report a realization of a Sagnac-type interferometer with cold atoms. Cold rubidium atoms are prepared in a magneto-optical trap and are pushed by resonant laser pulse to form slow atomic beam. In the interference region, atomic wave packets are coherently manipulated using pi/2 - pi - pi/2 Raman pulse sequences. Interference fringes with maximum contrast of 37% are observed experimentally.

Bohmian mechanics to high-order harmonic generation

This paper introduces Bohmian mechanics (BM) into the intense laser-atom physics to study high-order harmonic generation. In BM, the trajectories of atomic electrons in intense laser field can be obtained with the Bohm-Newton equation. The power spectrum with the trajectory of an atomic electron is calculated, which is found to be irregular. Next, the power spectrum associated with an atom ensemble from BM is considered, where the power spectrum becomes regular and consistent with that from quantum mechanics. Finally, the reason of the generation of the irregular spectrum is discussed.This paper introduces Bohmian mechanics (BM) into the intense laser-atom physics to study high-order harmonic generation. In BM, the trajectories of atomic electron in an intense laser field can be obtained with the Bohm–Newton equation. The power spectrum with the trajectory of an atomic electron is calculated, which is found to be irregular. Next, the power spectrum associated with an atom ensemble from BM is considered, where the power spectrum becomes regular and consistent with that from quantum mechanics. Finally, the reason of the generation of the irregular spectrum is discussed.

Optical Guiding of Trapped Atoms by a Blue-Detuned Hollow Laser Beam in the Horizontal Direction

Optical guiding of Rb-85 atoms in a magneto-optical trap (MOT) by a blue-detuned horizontal hollow laser beam is demonstrated experimentally. The guiding efficiency and the velocity distribution of the guided atoms are found to have strong dependence on the detuning of the guiding laser. In particular, the optimum guiding occurs when the blue detuning of the hollow laser beam is approximately equal to the hyperfine structure splitting of the Rb-85 ground states, in good agreement with the theoretical analysis based on a three-level model.

A peculiar tripartite entangled state

We present a scheme to prepare two-atom Einstein-Podoisky-Rosen states and three-atom entangled states via cavity quantum electrodynamics, and it can be realized experimentally. Importantly, we find that in the set of tripartite entangled states prepared by our scheme there is a peculiar tripartite entangled state except the Greenberger-Horne-Zeilinger (GHZ) state. The peculiar tripartite entangled states have double feature of the GHZ state (i.e. tau(123) > 0) and W state (i.e. the remaining reduce density matrices rho(ij) retain entanglement according to the positive partial transformation (PPT) criterion) simultaneously. However, its entanglement properties are not completely identical either to the GHZ state or to the W state. It is interesting that for peculiar entanglement properties, the remaining reduced density matrices rho(ij) can retain entanglement or disentanglement independently, which can be chosen freely according to our need.

Direct measurement of light speed reduction in a rubidium vapour medium coherently prepared by electromagnetically induced transparency

We have experimentally observed the reduction of light speed in a rubidium vapour medium coherently prepared by electromagnetically induced transparency. The light speed reduction was deduced by directly measuring the time delay of a probe light when it passed through the medium. The time delay varies with the intensity of the coupling laser, and the typical time delay we recorded was 1.8 μs, corresponding to a light speed of 56000 m/s.

Chip-Based Square Wave Dynamic Micro Atom Trap

We propose a scheme for a chip-based dynamic micro atom trap where the trap potentials are created by square wave radiation and an inhomogeneous static magnetic field. The parameters of this kind of trap array can be modulated dynamically. Both one-dimensional (1-D) and two-dimensional (2-D) trap array potentials for 6Li atoms are discussed. The 1-D trap is combined by a square wave radiation (6 kHz) and a gradient magnetic field (300 G/cm), the array constant of 1-D trap is 0.85 μm. Since the trap array does not require any laser field, it can be easily integrated on a chip and it is useful in applications of scalable quantum information processing.