Xiaodong He

Trapping a single atom in a blue detuned optical bottle beam trap

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.

Rotating single atoms in a ring lattice generated by a spatial light modulator

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.

High efficient loading of two atoms into a microscopic optical trap by dynamically reshaping the trap with a spatial light modulator

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.

Entangling Two Individual Atoms of Different Isotopes via Rydberg Blockade.

We report on the first experimental realization of the controlled-not (cnot) quantum gate and entanglement for two individual atoms of different isotopes and demonstrate a negligible cross talk between two atom qubits. The experiment is based on a strong Rydberg blockade for ^{87}Rb and ^{85}Rb atoms confined in two single-atom optical traps separated by 3.8  μm. The raw fidelities of the cnot gate and entanglement are 0.73±0.01 and 0.59±0.03, respectively, without any corrections for atom loss or trace loss. Our work has applications for simulations of many-body systems with multispecies interactions, for quantum computing, and for quantum metrology.

Combining red and blue-detuned optical potentials to form a Lamb-Dicke trap for a single neutral atom

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.

Interaction-induced decay of a heteronuclear two-atom system

Two-atom systems in small traps are of fundamental interest for understanding the role of interactions in degenerate cold gases and for the creation of quantum gates in quantum information processing with single-atom traps. One of the key quantities is the inelastic relaxation (decay) time when one of the atoms or both are in a higher hyperfine state. Here we measure this quantity in a heteronuclear system of 87Rb and 85Rb in a micro optical trap and demonstrate experimentally and theoretically the presence of both fast and slow relaxation processes, depending on the choice of the initial hyperfine states. This experimental method allows us to single out a particular relaxation process thus provides an extremely clean platform for collisional physics studies. Our results have also implications for engineering of quantum states via controlled collisions and creation of two-qubit quantum gates.