Far-off Resonance Optical Dipole Research Articles

Optical Dipole Trap for Laser-Cooled Lithium-7 Atoms

In this work, we discuss a far-off resonance optical dipole trap for cold lithium-7 atoms. A single optical trapping beam was produced by a continuous-wave fiber laser. Using our experimental data, we obtained important parameters of the trap, such as size of the cold atomic cloud, and evaluate the dipole potential and the rate of the trap losses. Information on temperature is acquired from observation of parametric resonances. We investigate the parametric resonances obtained with strong modulation of the trap potential and record superharmonics. We plan to prepare ultra-cold gas of highly-excited lithium atoms and study interactions between Rydberg atoms.

Measurement and extinction of vector light shifts using interferometry of spinor condensates

We use differential Ramsey interferometry of ultracold atoms to characterize the vector light shift (VLS) from a far-off resonance optical dipole trap at $\lambda = 1064\,\mathrm{nm}$. The VLS manifests as a `fictitious' magnetic field, which we perceive as a change in the Larmor frequency of two spinor condensates exposed to different intensities of elliptically polarized light. We use our measurement scheme to diagnose the light-induced magnetic field and suppress it to $2.1(8)\times10^{-4}$ of its maximum value, by making the trapping light linearly polarized with a quarter-wave plate in each beam. Our sensitive measurement of the VLS-induced field demonstrates high-precision, in-vacuo interferometric polarimetry of dipole trapping light and can be adapted to measure vector shifts from other lasers, advancing the application of optically trapped atoms to precision metrology.

Comparison of loading double-loop microtraps from a surface MOT and a FORT

Two methods to load a microtrap consisting of two concentric microwire loops of radii 300 and 660 μm carrying oppositely oriented currents are demonstrated. Atoms can be directly loaded into the microtrap from a surface magneto-optical trap or alternatively using a far-off resonance optical dipole trap (FORT) as an intermediate step. About 1 × 105 87Rb atoms can be loaded into the microtrap using either technique although the FORT achieves a lower temperature. The FORT is well suited to loading a linear array of 3 microtraps that are aligned with the propagation direction of the infrared laser. Atoms can be trapped in either the $$5S_{1/2}\;F=1$$ or 2 ground state hyperfine level. The position of the microtrapped atom cloud can be precisely adjusted using a bias magnetic field over a distance of 350 to slightly <50 μm from the atom chip surface.

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.

Laser-driven Sisyphus cooling in an optical dipole trap

We propose a laser-driven Sisyphus-cooling scheme for atoms confined in a far-off resonance optical dipole trap. Utilizing the differential trap-induced ac Stark shift, two electronic levels of the atom are resonantly coupled by a cooling laser preferentially near the trap bottom. After absorption of a cooling photon, the atom loses energy by climbing the steeper potential, and then spontaneously decays preferentially away from the trap bottom. The proposed method is particularly suited to cooling alkaline-earth-metal-like atoms where two-level systems with narrow electronic transitions are present. Numerical simulations for the cases of ${}^{88}$Sr and ${}^{174}$Yb demonstrate the expected recoil and Doppler temperature limits. The method requires a relatively small number of scattered photons and can potentially lead to phase-space densities approaching quantum degeneracy in subsecond time scales.

Resonant Control of Elastic Collisions in an Optically Trapped Fermi Gas of Atoms

We have loaded an ultracold gas of fermionic atoms into a far-off resonance optical dipole trap and precisely controlled the spin composition of the trapped gas. We have measured a magnetic-field Feshbach resonance between atoms in the two lowest energy spin states, /9/2,-9/2> and /9/2,-7/2>. The resonance peaks at a magnetic field of 201.5+/-1.4 G and has a width of 8.0+/-1.1 G. Using this resonance, we have changed the elastic collision cross section in the gas by nearly 3 orders of magnitude.

Cold-atom accumulation using an optical trap door

Experiments are performed on loading cold atoms into a far-off resonance optical dipole trap that is spatially separated from the laser-cooling region. The atoms are delivered using a far-off resonant optical dipole guide and enter the trap through a switchable blue-detuned light sheet or ``trap door.'' This scheme provides a means to transfer atoms from a dissipative to a non-dissipative trap without a significant loss of phase-space density. We study the dynamics of atoms within the trap and measure their lifetime. Preliminary results on multiple loading are presented. As the technique does not rely on near-resonant light, the atom number limit characteristic of laser-cooling experiments can, in principle, be exceeded.

Photoassociation spectrum of ultracold Rb atoms.

We study the photoassociative collisional loss of laser-cooled Rb atoms from a far-off resonance optical dipole force atom trap. We obtain a well-resolved photoassociation spectrum from 50 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ to 980 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ below the first excited dissociation limit of the ${\mathrm{Rb}}_{2}$ molecule. Two vibrational series associated with excited ${\mathrm{Rb}}_{2}$ $^{3}\mathrm{\ensuremath{\Sigma}}_{\mathit{g}}^{+}$ states are clearly visible. Oscillations in the associated Franck-Condon factors reflect the structure of the triplet ground state wave function. Our results clearly demonstrate the potential of photoassociation spectroscopy as a new probe of molecular structure.