We present an asymmetric focused-beam trap of rubidium-85 atoms where the cloud volume only varied with the trap laser intensity. By repumping on F=2 to F'=2 D2 transition, the Stokes Raman scattering has strongly affected the population ratio in the two hyperfine ground states. With the volume and trap number simultaneously and separately controlled, we have shown that the cloud density can be monotonously manipulated from zero to the maximum value limited by the cooling power. By solely varying the intensity of repump laser, the scheme for precision loading of exact 1-6 atoms in the FORT, which is beyond the practical loading limit of the blue-detuned light-assisted collision, is described.
We present an asymmetric focused-beam trap of rubidium-85 atoms where the cloud volume only varied with the trap laser intensity. By repumping on F=2 to F'=2 D2 transition, the Stokes Raman scattering has strongly affected the population ratio in the two hyperfine ground states. With the volume and trap number simultaneously and separately controlled, we have shown that the cloud density can be monotonously manipulated from zero to the maximum value limited by the cooling power. By solely varying the intensity of repump laser, the scheme for precision loading of exact 1-6 atoms in the FORT, which is beyond the practical loading limit of the blue-detuned light-assisted collision, is described.
We present an asymmetric focused-beam trap (FBT) of cold Rubidium-85 atoms.Unlike the cold atom preparation using the magneto-optical trap, the FBT has its path of cooling beam occupying only one axis.Since the experiments on these cold atoms usually require additional laser beams or other atom interacting sources, the FBT allows more optical and physical accessibility for these experiments.In our experiment, the cooling beams only occupied one axis, and the crossed repumping beams were in the transverse plane to the cooling beams.By varying the intensity of the repump laser, we have shown that the atomic cloud density can be monotonically manipulated from zero to the maximum value limited by the cooling power.With this monotonic control, we then computationally introduced a scheme for the precision loading of 1-6 atoms into the far-off-resonance optical dipole trap (FORT).Using the FBT for precision FORT loading could enable extensions toward the research areas, such as Rydberg atom, quantum simulation, and quantum computing.
We report a way to overcome heating due to the reabsorption of scattered light when relatively many atoms are laser cooled at high density. A sample of $8\ifmmode\times\else\texttimes\fi{}{10}^{7}\mathrm{Cs}$ atoms, with $6\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{atoms}\mathrm{}\mathrm{cm}}^{\mathrm{\ensuremath{-}}3},$ is loaded into a deep far-detuned one-dimensional optical lattice, which acts as a large volume three-dimensional (3D) trap. Polarization gradient cooling with a separate set of cooling beams is found to work well in this trap, populating the trap's vibrational ground state with more than half the atoms. After cooling, the lattice is shut off adiabatically, leaving a still dense sample at 1.2 \ensuremath{\mu}K. We propose and demonstrate a generalization to a 3D lattice, which will allow many more atoms to be loaded into conservative light traps, and can greatly increase the initial phase-space density for loading magnetic traps.
We experimentally realize an enhanced Raman control scheme for neutral atoms that features an intrinsic suppression of the two-photon carrier transition, but retains the sidebands which couple to the external degrees of freedom of the trapped atoms. This is achieved by trapping the atom at the node of a blue detuned standing wave dipole trap, that acts as one field for the two-photon Raman coupling. The improved ratio between cooling and heating processes in this configuration enables a five times lower fundamental temperature limit for resolved sideband cooling. We apply this method to perform Raman cooling to the two-dimensional vibrational ground state and to coherently manipulate the atomic motion. The presented scheme requires minimal additional resources and can be applied to experiments with challenging optical access, as we demonstrate by our implementation for atoms strongly coupled to an optical cavity.
Summary form only given.Laser cooling, where excess kinetic energy is extracted by a photon, is ideally suited to loading atoms into a trap; however, quantization and reabsorption of light, limit the maximum phase-space density attainable. A sequence of laser cooling followed by evaporative cooling, where the excess energy is extracted by escaping atoms, may be used to overcome the laser cooling limit; however, such a scheme dramatically reduces the number of trapped atoms. A remaining challenge is to achieve continuous loading without the phase-space density limit imposed by near-resonant light. We consider continuous evaporative loading of a magnetic trap using a magnetically insensitive buffer gas. The key is to deliver sufficient cold atoms to the trapping region such that the steady-state trap population is large. To achieve this we employ an atomic fountain guided by a far-off resonant laser beam. At the apex of the fountain, the density can be a factor of 30-40 higher than in a magneto-optical trapping region, and importantly, the atoms are spatially separated from the region of resonant laser light. We propose to use this high-density region as a reservoir for continuous evaporative loading of a trap.
We report cooling and trapping of 85Rb atoms in the lower hyperfine level F=2 of the 52S1∕2 ground state in a magneto-optical trap. A maximum of $\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{6}$ atoms could be trapped using trap laser frequency red detuned by 12MHz from the $F=2\ensuremath{\rightarrow}{F}^{\ensuremath{'}}=1$ cycling transition. The loading behavior of the trap in terms of loading rate, collisional loss rate, number and density of trapped atoms was studied as a function of trap laser intensity.
This dissertation reports on the design, construction, and investigation of a pulsed optical dipole force trap which uses laser light to confine ultracold rubidium (Rb) atoms. Because the laser frequency is detuned far from the atomic resonance frequency, the optical dipole force trap is also called a "far-off-resonance trap" (FORT). The use of pulsed laser light to create an optical trap may find application in expanding the number of atomic species which can be confined. The experiments reported here are principally aimed, however, at understanding the physics of pulsed FORT dynamics in anticipation of using the free electron laser (FEL) at Jefferson Lab (Jlab) to construct a FORT. The Jlab FEL will provide a tunable, high power laser light source enabling the realization of spatially large and/or energetically deep traps which are not presently accessible with table-top laser sources. Here, a mode-locked Nd:YAG laser is used as a pulsed laser source. Since the conservative optical dipole force trap does not cool Rb atoms, ultracold atoms must be loaded into the FORT. The optical dipole force trap is formed at the focus of a Gaussian, 1.06 μm Nd:YAG laser beam which is located at the center of a high vacuum chamber and superimposed onto the center of a pre-cooled Rb atom cloud that has been previously accumulated in a magneto-optic trap (MOT). The performance of the pulsed FORT is compared to a continuous wave mode (cw) FORT which is built using the same laser beam; the operation of the two kinds of FORTs can be switched easily without disturbing the experimental alignment. The dependencies of FORT loading efficiency to FORT and MOT parameters such as FORT laser power, loading time, storage/holding time, detuning of the primary MOT laser frequency, and repump laser intensity are investigated. There are about 1.5×107 ultracold rubidium atoms in the MOT. At 7 Watts FORT laser power, about 8% of the atoms are loaded successfully into the cw FORT and about 5% into the pulsed FORT under similar, but not identical, conditions. In most respects both the cw and pulsed FORTs show comparable behavior. The behavior of both FORTs depends strongly on FORT laser power. As expected, at higher power, more atoms can be loaded into the FORT. Both FORTs also depend on the loading time and holding time.