The continuous injection and propagation of a cold atomic beam in a 1.7 m long high-gradient (up to 2.7 kG/cm) magnetic guide is demonstrated. Continuous injection is accomplished by side-loading a magnetic guide with atoms from a sequence of two modified magneto-optical traps. In the high-gradient portion of the guide, the guided atomic beam has a transverse temperature of 420 muK +/- 40 muK, a longitudinal temperature of 1 mK, and an average velocity of order 1 m/s. Essential for the characterization of this steady-state atomic beam, imaging methods compatible with the high field-gradients associated with this magnetic guide have been investigated and developed. By utilizing a probe laser tuned to an open transition, the fluorescence yield per atom is largely fixed throughout the trap volume, independent of the trapping field. This enables a reliable conversion of fluorescence images into atomic-density profiles. Using a fixed radio-frequency (nurf) current coupled directly onto the guide wires, continuous and selective removal of atoms with a transverse energy exceeding hnurf is demonstrated. This removal scheme is the essence of an rf filter, where the number of modes occupied by the atomic flow is reduced. Through sufficient rf-filtering, a near-single-mode guided atomic beam should be achievable, enabling basic atom-interferometric experiments. The extension of this fixed-frequency removal of atoms for continuous position-resolved evaporative cooling in a long magnetic guide is outlined. Employing an innovative gridless technique for performing Direct Simulation of rarefied gas dynamics via Monte Carlo (DSMC), the evaporative cooling process in a guided atomic beam has been simulated. Both fixed-frequency as well as variable-frequency evaporative cooling layouts have been explored and the results of these simulations are presented. The implementation of this gridless technique is presented and its benefits are briefly outlined. In parallel with the development of a continuous-wave atom laser, tools suited to manipulate cold atomic beams in atom guides have been explored. An atomic guide with a tunable aspect ratio, using rf-dressed state potentials, is presented.
The continuous injection and propagation of a cold atomic beam in a 1.7 m long high-gradient (up to 2.7 kG/cm) magnetic guide is demonstrated. Continuous injection is accomplished by side-loading a magnetic guide with atoms from a sequence of two modified magneto-optical traps. In the high-gradient portion of the guide, the guided atomic beam has a transverse temperature of 420 muK +/- 40 muK, a longitudinal temperature of 1 mK, and an average velocity of order 1 m/s. Essential for the characterization of this steady-state atomic beam, imaging methods compatible with the high field-gradients associated with this magnetic guide have been investigated and developed. By utilizing a probe laser tuned to an open transition, the fluorescence yield per atom is largely fixed throughout the trap volume, independent of the trapping field. This enables a reliable conversion of fluorescence images into atomic-density profiles. Using a fixed radio-frequency (nurf) current coupled directly onto the guide wires, continuous and selective removal of atoms with a transverse energy exceeding hnurf is demonstrated. This removal scheme is the essence of an rf filter, where the number of modes occupied by the atomic flow is reduced. Through sufficient rf-filtering, a near-single-mode guided atomic beam should be achievable, enabling basic atom-interferometric experiments. The extension of this fixed-frequency removal of atoms for continuous position-resolved evaporative cooling in a long magnetic guide is outlined. Employing an innovative gridless technique for performing Direct Simulation of rarefied gas dynamics via Monte Carlo (DSMC), the evaporative cooling process in a guided atomic beam has been simulated. Both fixed-frequency as well as variable-frequency evaporative cooling layouts have been explored and the results of these simulations are presented. The implementation of this gridless technique is presented and its benefits are briefly outlined. In parallel with the development of a continuous-wave atom laser, tools suited to manipulate cold atomic beams in atom guides have been explored. An atomic guide with a tunable aspect ratio, using rf-dressed state potentials, is presented.
We demonstrate the continuous injection and propagation of a cold atomic beam in a high-gradient (up to 2.7kG∕cm) magnetic guide of 1.7m length. Continuous injection is accomplished using a side-loading scheme that involves a sequence of two modified magneto-optic traps. Methods are developed to measure the atomic-flow temperatures and the flux under steady-state conditions. In the high-gradient portion of the guide, the guided atomic beam has a transverse temperature of $420\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}\ifmmode\pm\else\textpm\fi{}40\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$, a longitudinal temperature of 1mK, and an average velocity of order 1m∕s. Using a radio-frequency current of a fixed frequency $\ensuremath{\nu}$ coupled directly into the guide wires, atoms exceeding a transverse energy of $h\ensuremath{\nu}$ can be continuously and selectively removed from the atomic beam.
We demonstrate experimentally the continuous and pulsed loading of a slow and cold atomic beam into a magnetic guide. The slow beam is produced using a vapor loaded laser trap, which ensures two-dimensional magneto-optical trapping, as well as cooling by a moving molasses along the third direction. It provides a continuous flux larger than 109 atoms/s with an adjustable mean velocity ranging from 0.3 to 3 m/s, and with longitudinal and transverse temperatures smaller than 100μK. Up to 3108 atoms/s are injected into the magnetic guide and subsequently guided over a distance of 40 cm.
This thesis examines two complimentary methods for the laser cooling of a magnetically guided ultra-cold atom beam. If combined, these methods could serve as a starting point for high-through put and possibly even continuous production of Bose-Einstein condensates. First, a mechanism is outlined to harvest ultra cold atoms from a magnetically guided atom beam into an optical dipole trap. A continuous loading scheme is described that dissipates the directed kinetic energy of a captured atom via deceleration by a magnetic potential barrier followed by optical pumping to the energetically lowest Zeeman sublevel. The application of this scheme to the transfer of ultra cold chromium atoms from a magnetically guided atom beam into a deep optical dipole trap is investigated via numerical simulations of the loading process. Based on the results of the theoretical studies the feasibility and the efficiency of our loading scheme, including the realisation of a suitable magnetic field configuration, are analysed. Second, experiments were conducted on the transverse laser cooling of a magnetically guided beam of ultra cold chromium atoms. Radial compression by a tapering of the guide is employed to adiabatically heat the beam. Inside the tapered section heat is extracted from the atom beam by a two-dimensional optical molasses perpendicular to it, resulting in a significant increase of atomic phase space density. A magnetic offset field is applied to prevent optical pumping to untrapped states. Our results demonstrate that by a suitable choice of the magnetic offset field, the cooling beam intensity and detuning, atom losses and longitudinal heating can be avoided. Final temperatures below 65 µK have been achieved, corresponding to an increase of phase space density in the guided beam by more than a factor of 30.
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.
The atom laser has long been a holy grail within atom physics and with the creation of an atom laser we hope to bring a similar revolution in to the field of atom optics. With the creation of the Bose-Einstein Condensate (BEC) in 1995 the path to an atom laser was initiated. An atom laser is continues source of BEC. In a Bose condensate all the atoms occupy the same quantum state and can be described by the same wave function and phase. With an atom laser the De Broglie wavelength of atoms can be much smaller than the wavelength of light. Due to the ultimate control over the atoms the atom laser is very interesting for atom optics, lithography, metrology, etching and deposition of atoms on a surface. All previous atom lasers have been created from atoms coupled out from an existing Bose-Einstein Condensate. There are different approaches but common to them all is that the duration of the output of the atom laser is limited by the size of the initial BEC and they all have a low flux. This leaves the quest to build a continuous high flux atom laser. An alternative approach to a continuous BEC beam is to channel a continuous ultra cold atomic beam into a magnetic guide and then cool this beam down to degeneracy. Cooling down a continuous beam of atoms faces three large problems: The collision rate has to be large enough for effective rethermalization, since evaporative cooling in 2D is not as effective as in 3D and a large thermal conductivity due to atoms with a high angular momentum causes heating downstream in the guide. We have built a 4 meter magnetic guide that is placed on a downward slope with a magnetic barrier in the end. In the guide we load packets of ultra cold rubidium atoms with a frequency rate large enough for the packets to merge together to form a continuous atomic beam. The atomic beam is supersonic and when the beam reaches the end barrier it will return and collide with itself. The collisions lowers the velocity of the beam into subsonic velocities and a shock wave is created between the two velocity regions. In order to conserve number of particle, momentum and enthalpy the density of the atomic beam passing through the shock wave must increase. We have build such a shock wave in an atomic beam and observed the density increase due to this. As an extra feature having a subsonic beam on a downward slope adds an extra density increase due to gravitational compression. Loading ultra cold atoms into a 3D trap from the dense subsonic beam overcomes the problem with 2D cooling and thermal conductivity. This was done and evaporative cooling was applied creating an unprecedented large number rubidium BEC.
Atom optics has been a highly active field of research with many scientific breakthroughs over the past two decades, largely due to successful advances in laser technology, microfabrication techniques, and the development of laser cooling and trapping of neutral atoms. This dissertation details several atom optics experiments with the motivation to develop tools and techniques for precision atom wave interferometry. It provides background information about atom optics and the fundamentals behind laser cooling and trapping, including basic techniques for cold gas thermometry and absorptive detection of atoms. A brief overview of magnetic trapping and guiding in tight wire-based traps is also provided before the experimental details are presented. ❧ We developed a novel laser source of 780 nm light using frequency-doubled 1560 nm fiber amplifier. This laser system provided up to a Watt of tunable frequency stabilized light for two Rb laser cooling and trapping experiments. One system generates Bose-Einstein condensates in an optical trap while the second is based on atom chip magnetic traps. The atom chip system, detailed in this thesis, was designed and built to develop the tools necessary for transport and loading large numbers of cold atoms and explore the potential for guided atom interferometry. Techniques and results from this experiment are presented, including an efficient magnetic transport and loading method to deliver cold atom to atom chip traps. We also developed a modeling tool for the magnetic fields formed by coiled wire geometries, as well as planar wire patterns. These models helped us design traps and determine adiabatic transportation of cold atoms between macro-scale traps and micro-traps formed on atom chips. Having achieved near unity transfer efficiency, we demonstrated that this approach promises to be a consistent method for loading large numbers of atoms into micro-traps. Furthermore, we discuss an in situ imaging technique to investigate magnetic field contours of the traps and the dynamics of atoms within those confining potentials. We also controlled the propagation along the atom chip guides by accelerating atoms with longitudinal magnetic gradients, and investigated an atom focusing scheme. ❧ While the atom chip wire guides perform a role analogous to optical fibers guiding light waves, ""free space"" cold atoms offer great opportunity for precision interferometry. We describe a second on-going atom optics experiment that measures gravity gradients using a pair of atom fountain interferometers separated by one meter. We have demonstrated Gravity Gradiometer resolution down to 4x10⁻⁹ g/m using a 40 kg test mass. The atomic physics subsystem is described in detail, including the vacuum, cold atom source, optics, magnetic coils and shields, and vibration isolation and compensation. The system is designed to be a compact, robust, transportable instrument, taking strides towards future gravity gradient measurements in the field. In the realm of space applications, there has been interest for micro-gravity science experiments aboard the International Space Station, along with instrument development for gravity mapping of Earth and planetary bodies with satellite-based instruments. Furthermore, there are ground-based applications for gravity imaging of local density distributions, precision measurement of gravity, as well as proposals for redefining the kilogram, detecting gravitational waves and determining the Gravitational constant.