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ABSTRACT: We propose and demonstrate a scheme for strong radial confinement of a single 87 Rb atom by a bichromatic far-off resonance optical dipole trap (BFORT). The BFORT is composed of a blue-detuned Laguerre-Gaussian LG01 beam and a red-detuned Gaussian beam. The atomic oscillation frequency measurement shows that the effective trapping dimension is much sharper than that from a diffraction-limited microscopic objective. Theory shows that the added scattering rate due to imposing blue-detuned light is negligible when the temperature of the single atoms is close to ground state temperature. By carrying out sub-Doppler cooling, the mean energy of single atoms trapped in the BFORT is reduced to 15 ± 1 μK. The corresponding mean quantum number of radial vibration n is about 1.65, which satisfies the Lamb-Dicke regime. We conclude that the BFORT is a suitable Lamb-Dicke trap for further cooling a single neutral atom down to the ground state and for further application in quantum information processing.
Optics Express 02/2012; 20(4):3711-24. · 3.59 Impact Factor
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ABSTRACT: We propose and demonstrate a scheme for strongly radially confining a single
neutral atom in a bichromatic far-off resonance optical dipole trap(BFORT) .
BFORT is composed of a blue-detuned Laguerre-Gaussian $LG^1_ 0$ beam and a
red-detuned Gaussian beam. The trapping radial dimension of a single atom
trapped in the Gaussian FORT can be greatly compressed by imposing a
blue-detuned Laguerre-Gaussian $LG^1_ 0$ beam with moderate potential depth. By
modulating the potential depth of the Gaussian FORT we observed that the
resonant and parametric excitation of the oscillatory motion of a single atom
in this BFORT and obtained the oscillation frequency that well fits prediction
from the theoretical model. The frequency measurement shows that effective
trapping dimension can be greatly sharper than that diffraction limited of
microscopic objective we used. Then we show that the excess scattering rate due
to imposing blue detuned light can be eliminated when single atoms is close to
ground-state theoretically. So BFORT suits the purpose of acting as a
Lamb-Dicke trap for further cooling a single neutral atom to motion
ground-state and finding application in quantum information progressing.
11/2010;
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ABSTRACT: We demonstrate trapping a single rubidium atom in a blue detuned optical bottle beam trap. The trap was formed by a strongly focused blue detuned laser beam, which passes through a computer-generated circular pi phase hologram displayed on a spatial light modulator. Single atoms were loaded from a magneto-optical trap and stored in the optical trap for several seconds.
Optics Letters 07/2010; 35(13):2164-6. · 3.40 Impact Factor
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ABSTRACT: We demonstrated trapping two neutral (87)Rb atoms in a two site optical ring lattice generated by reflecting a single laser beam from a computer controlled spatial light modulator directly. The ring lattice was transformed into a Gaussian trap by dynamically displaying the holograms animation movie on the modulator. The trapped atoms follow the evolution of traps and move into the same microscopic dipole trap at the end. The detected success rate of this manipulation is larger than 90%. Under imposing the near resonance light, we observed strong light-induce collision between two atoms.
Optics Express 06/2010; 18(13):13586-92. · 3.59 Impact Factor
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ABSTRACT: We demonstrated trapping single neutral Rb atoms in micro traps of an optical ring lattice formed by superposing the +/-l components of the Laguerre-Gaussian mode, and generated by reflecting a single laser beam from a computer controlled spatial light modulator. A single atom in one trap or two atoms with one each in two traps were identified by observing the fluorescence. The trap array loaded with single atoms was rotated by dynamically displaying the hologram animation movie on the modulator. The modulation period in the fluorescence indicates the rotation of one or two single atoms in the lattice.
Optics Express 11/2009; 17(23):21007-14. · 3.59 Impact Factor
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ABSTRACT: A theoretical approach to quantitatively estimate the spin polarization enhancement via spin polarization-induced nuclear Overhauser effect (SPINOE) in solid state is presented. We show that theoretical estimates from the model are in good agreement with published experimental results. This method provides a straightforward way to predict the enhanced factor of nuclear magnetic resonance signals in solid state experiments.
Journal of Magnetic Resonance 12/2008; 196(2):200-3. · 2.14 Impact Factor
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ABSTRACT: A Raman-amplified atomic filter is demonstrated experimentally. With a coupling light detuned from the D2 line of 85Rb, a weak signal light can be amplified by a factor of 55, and the bandwidth of the filter's transmission spectrum is narrowed to approximately 60 MHz. Moreover, the transmission wavelength is adjustable by changing the coupling-light frequency. Compared with a conventional dispersive atomic filter, this Raman-amplified atomic filter could be more efficient to suppress background noise in free-space quantum-key distribution or a laser-communication system.
Optics Letters 09/2008; 33(16):1842-4. · 3.40 Impact Factor
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ABSTRACT: In this article the recent experimental works on cold atoms carried out at Wuhan Institute of Physics and Mathematics (WIPM) are reported. These include the experimental realization of Bose-Einstein condensation (BEC), different type of cold atom interferometers, and bichromatic electromagnetically-induced transparency (EIT). We have realized Bose-Einstein condensates of 87Rb dilute atomic gases. The apparatus consists of two horizontally mounted magneto-optic-traps (MOTs) and a QUIC magnetic trap. Nearly 3×108 atoms were trapped in the second MOT, and up to 1.2×108 atoms were adiabatically transferred to the QUIC trap. A pure condensate with about 1.1×105 atoms at about 30 nK was achieved. We also demonstrated two type of cold atom interferometers, the Sagnac and Ramsey interference fringes were recorded with contrast of up to 37%.
Journal of Physics Conference Series 09/2007; 80(1):012047.
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ABSTRACT: We consider the particle–hole excitation energy for the insulator state of an ultracold atomic Bose system created by increasing non-adiabatically the depth of an optical lattice. We give the analytical expression of this excitation energy, and it is found that the excitation energy is quite different from that of the ordinary Mott insulator state created by adiabatically increasing the depth of the optical lattice. This difference physically arises from the different particle-number fluctuations in the lattice sites for the insulator state created adiabatically or non-adiabatically.
Journal of Physics B Atomic Molecular and Optical Physics 01/2007; 40(3):517. · 1.88 Impact Factor
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ABSTRACT: After removing the double-well potential trapping two initially independent Bose condensates, the density expectation value is calculated when both the exchange symmetry of identical bosons and interatomic interaction are considered. The density expectation value and evolution equations are obtained based on both the first-quantization and second-quantization methods. When the interatomic interaction is considered carefully, after the overlapping of two initially independent condensates, it is shown that there is a nonzero interference term in the density expectation value. It is found that the calculated density expectation value with this model agrees with the interference pattern observed in the experiment by Andrews (Science 275, 637 (1997)). The nonzero interference term in the density expectation value physically arises from the exchange symmetry of identical bosons and interatomic interaction which make two initially independent condensates become coherent after the overlapping. For two initially independent condensates, our researches show that there is an interaction-induced coherence process.
12/2006;
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ABSTRACT: By using Rb vapor filters, free-space quantum key distribution with the B92 protocol was realized experimentally; the filters based on the Faraday anomalous dispersion effect were used to suppress strong background light. With these atomic filters as spectral filtering, average transmission rates of sifted keys and corrected keys have reached as high as 3.14 and 1.56 kbits/s, respectively, while the error rate was maintained at a reasonable low level of 5.10%. The experimental results show that our Rb vapor filters with transmission efficiency of around 60% operate well under the condition of the mean photon number ⩽ 0.1.
Applied Physics Letters 11/2006; 89(19):191121-191121-3. · 3.84 Impact Factor
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ABSTRACT: For two-component Fermi gases at zero temperature, through a general derivation based on the BCS wave function, our research shows that the nonuniform molecular Bose-Einstein condensate has off-diagonal long-range order and can be described well by an order parameter when the size of molecules is much smaller than the size of the whole system. We also give the equation of state and nonlinear evolution equation for the order parameter of nonuniform molecular condensates, which is similar to the Gross-Pitaevskii equation of atomic Bose condensate. The nonlinear evolution equation is applied to consider the Josephson effect for two weakly linked molecular condensates in the presence of nonuniform magnetic field. We find clear particle-number oscillation where spatially dependent binding energy of molecules plays an important role.
Phys. Rev. A. 09/2006; 74(3).
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ABSTRACT: We consider the Josephson effect when two independent Bose superfluids are weakly connected. In the presence of interparticle interaction and based on the calculations of the one-particle density matrix of the whole system, we find that the one-particle density matrix can be factorized which satisfies the general criterion of Bose superfluid proposed by Penrose and Onsager. By introducing an effective order parameter for the whole system, our researches show that there is Josephson effect for two independent Bose superfluids. Comment: 9 pages, 4 figures. two typos in Eqs. (19) and (22) are corrected in this version
06/2006;
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ABSTRACT: We study theoretically the ultracold two-component fermionic gases when a gradient magnetic field is used to tune the scattering length between atoms. For 6Li at the narrow resonance B0=543.25 G, it is shown that the gases would be in a coexistence of the regimes of BCS, Bose-Einstein condensation (BEC), and unitarity limit with the present experimental technique. In the case of thermal and chemical equilibrium, we investigate the density distribution of the gases and show that a double peak of the density distribution can give us a clear evidence for the coexistence of BCS, BEC, and unitarity limit.
Physical Review Letters 10/2005; 95(12):120401. · 7.37 Impact Factor
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09/2005;
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ABSTRACT: After removing the double-well potential trapping two initially independent Bose condensates, the density expectation value is calculated when both the exchange symmetry of identical bosons and interatomic interaction are considered. After the overlapping, it is shown that there is a nonzero interference term in the density expectation value. This nonzero interference term physically arises from the exchange symmetry of identical bosons and interatomic interaction which make two initially independent condensates become coherent after the overlapping. It is found that the calculated density expectation value with this model agrees with the interference pattern observed in the experiment by Andrews et al (Science 275, 637 (1997)).
08/2005;
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ABSTRACT: This Letter presents a two-dimensional nuclear magnetic resonance (NMR) approach for constructing a two-logical-qubit decoherence-free subspace (DFS) by using four multiple-quantum coherences of a CH3 spin system as logical qubits. The three protons in this spin system are magnetically equivalent and can only be used as a single qubit in one-dimensional NMR. We have experimentally demonstrated that our DFS can protect against more types of decoherences than those of the one composed of four noisy physical qubits all with different chemical shifts. This idea may provide new insights into extending qubit systems in the sense that it effectively utilizes the magnetically equivalent nuclei.
Physical Review Letters 08/2005; 95(2):020501. · 7.37 Impact Factor
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ABSTRACT: The thermodynamic properties of two-component Fermi gases with divergent scattering length is investigated and the transition temperature for the emergence of a stable dimeric gas is obtained by a simple theoretical model where the unique property of the dimers (i.e. fermionic atom pairs) with divergent scattering length is considered. Below the transition temperature, through the investigation of the overall entropy for the mixture gas of fermionic atoms and dimers, we calculate the relation between the energy and temperature of the system. In the limit of zero temperature, based on the chemical equilibrium condition, the fraction of the dimers is investigated and the role of the dimers in the collective excitations of the system is also discussed. It is found that our theoretical results agree with the condensate fraction, collective excitations, transition temperature and heat capacity investigated by the recent experiments about the strongly interacting two-component Fermi gases.
12/2004;
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ABSTRACT: We study theoretically the ultracold two-component Fermi gases when a gradient magnetic field is used to tune the scattering length between atoms. For Li6 at the narrow resonance B0=543.25G, it is shown that the gases would be in a coexistence of the regimes of BCS, BEC and unitarity limit with the present experimental technique. In the case of thermal and chemical equilibrium, we investigate the density distribution of the gases and show that a double peak of the density distribution can give us a clear evidence for the coexistence of BCS, BEC and unitarity limit.
12/2004;
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ABSTRACT: We present a theoretical model to investigate the interference of an array of Bose-Einstein condensates loaded in a one-dimensional spin-dependent optical lattice, which is based on an assumption that for the atoms in the entangled single-atom state between the internal and the external degrees of freedom each atom interferes only with itself. Our theoretical results agree well with the interference patterns observed in a recent experiment by Mandel et al. [Phys. Rev. Lett. 91, 010407 (2003)]. In addition, an experimental suggestion of nonuniform phase distribution is proposed to test further our theoretical model and prediction. The present work shows that the entanglement of a single atom is sufficient for the interference of the condensates confined in a spin-dependent optical lattice and this interference is irrelevant with the phases of individual condensates, i.e., this interference arises only between each condensate and itself and there is no interference effect between two arbitrary different condensates.
10/2004;
