This dissertation documents a second Bose-Einstein Condensate production apparatus at the University of Virginia. The apparatus produces condensates of 87 Rb atoms to be used as the wave source for atom interferometry experiments. Additionally, a new magnetic trap was developed which provides a harmonic potential with cylindrical symmetry and also supports the atoms against gravity. This trap is based on a time-orbiting potential. To characterize the trapping potential, a condensate was loaded into the trap and perturbed by suddenly changing the confinement field during loading. This had the effect of inducing harmonic oscillations which were measured at varying trap parameters. We expect that this trap will be useful for the implementation of a compact atom interferometer-based gyroscope. Finally, an asymmetric Bragg splitting pulse was developed which allowed for the implementation of two simple interferometers. These interferometers developed a phase which depended on the recoil frequency of 87 Rb and served as a proof of principle for this new apparatus.
This dissertation documents a second Bose-Einstein Condensate production apparatus at the University of Virginia. The apparatus produces condensates of 87 Rb atoms to be used as the wave source for atom interferometry experiments. Additionally, a new magnetic trap was developed which provides a harmonic potential with cylindrical symmetry and also supports the atoms against gravity. This trap is based on a time-orbiting potential. To characterize the trapping potential, a condensate was loaded into the trap and perturbed by suddenly changing the confinement field during loading. This had the effect of inducing harmonic oscillations which were measured at varying trap parameters. We expect that this trap will be useful for the implementation of a compact atom interferometer-based gyroscope. Finally, an asymmetric Bragg splitting pulse was developed which allowed for the implementation of two simple interferometers. These interferometers developed a phase which depended on the recoil frequency of 87 Rb and served as a proof of principle for this new apparatus.
We present a variant of the time-orbiting potential trap suitable for Bose-Einstein condensate atom interferometers, which provides weak, cylindrically symmetric confinement as well as support for the atoms against gravity. This trapping configuration is well-suited for the implementation of a compact atom interferometer based gyroscope. The trap is made up of six coils, which were produced using photolithographic techniques and take up a modest volume of approximately 1 cubic inch inside a vacuum chamber. The trapping frequencies and thermal characteristics of the trap are presented, showing cylindrical symmetry and scalability of the trapping frequencies from 1 Hz to 8 Hz in the symmetry plane.
A Bose-Einstein condensation (BEC) production machine has been assembled and operated, using two vacuum chambers isolated from each other by a thin tube. A magnetooptical trap (MOT) is operated in the first chamber, where atoms are captured out of a thermal vapor and cooled to about 200 µK. The atoms are then transferred to a magnetic trap which is mounted on to a movable stage. A programmable motor moves the stage about half a meter, carrying the atoms to the second vacuum chamber where they are evaporatively cooled in a time-orbiting potential trap. We successfully used this apparatus to observe the first BEC's at the University of Virginia. We have also implemented a novel atom trap for BEC's of 87 Rb to be used in atom interferometry experiments. The trap is based on a time-orbiting potential waveguide. It supports the atoms against gravity while providing weak confinement to minimize interaction effects. We have loaded a condensate into the waveguide, and removed all other confinement fields. Up to 2 ×10 4 condensate atoms have been loaded into the trap, at estimated temperatures as low as 850 pK. We expect this novel type of trap will be useful for a variety of applications in condensate interferometry. Finally, we have characterized our trap by perturbing the atomic cloud with a sudden change in the confinement field. We subsequently obtain harmonic oscillation frequencies vi (ω x ,ω y ,ω z ) as low as 2π×(6.0, 1.2, 3.3) Hz. We have developed a mathematical description of the waveguide fields to account for the residual fields from the trap leads, obtaining good agreement between the measured and predicted trap behavior. The weak confinement of our guide should greatly reduce the limiting effects of atomic interactions. We anticipate that interferometer measurement times of 1 s or more should be achievable in this device. With suitable modifications, our waveguide could be used to precisely measure electric polarizability, gravitational forces, rotations, and other phenomena. We expect that the trap design presented here will play an essential role in allowing condensate interferometry to realize its potential. Note: Abstract extracted from PDF text
We describe an atom trap for Bose-Einstein condensates of 87Rb to be used in atom interferometry experiments. The trap is based on a time-orbiting potential waveguide. It supports the atoms against gravity while providing weak confinement to minimize interaction effects. We observe harmonic oscillation frequencies $({\ensuremath{\omega}}_{x},{\ensuremath{\omega}}_{y},{\ensuremath{\omega}}_{z})$ as low as $2\ensuremath{\pi}\ifmmode\times\else\texttimes\fi{}(6.0,1.2,3.3)\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$. Up to $2\ifmmode\times\else\texttimes\fi{}{10}^{4}$ condensate atoms have been loaded into the trap, at estimated temperatures as low as 850pK. We anticipate that interferometer measurement times of 1s or more should be achievable in this device.
Since its first observation in 1995, Bose-Einstein condensation (BEC) experiments in dilute gases have been performed with only a few different kinds of magnetic traps. We have performed a BEC experiment with /sup 87/Rb atoms in a Ioffe-Pritchard magnetic potential, which opens up the possibility to study, e.g., Bose-Einstein condensates released in only one dimension. Our trap consists of a clip-like coil, which generates a pure two-dimensional (2D) quadrupole field for radial confinement. The axial confinement is provided by two plane pinch coils inside the clip-coil. These two coils create a bottle field. Two additional Helmholtz coils on the same symmetry axis are used to compensate the homogeneous part of the bottle field. By continuously varying the currents through the coils, the trapping potential can be changed from a 3D spherical harmonic to a 2D linear potential. The change can be done adiabatically or nonadiabatically by switching off the axial confinement slowly, or instantaneously respectively. This opens up the possibility to study 1D nonlinear atom optics. In combination with, e.g., far detuned light sheets, a Fabry-Perot type interferometer for a condensate might be realizable. Our experiments are performed in a vacuum system with two magneto-optical traps, which serves as the source of cold atoms for the magnetic trap. 10/sup 9/ atoms are captured in less than one minute. RF-induced evaporative cooling is used to increase the phase space density of the trapped atomic cloud. The BEC phase transition occurs at a temperature of 550 nK with 10/sup 6/ particles in the trap. Pure condensates with more than 10/sup 5/ atoms were produced.
Interferometry with atoms is a young discipline of physics. The ¯rst interfer- ometers were realised in the early 1990s, using light pulses as beamsplitters in momentum space. Recent developments in atom optics have led to new proposals for interferometers, where the splitting takes place spatially. Mag- netic and optical traps are both suited for this kind of interferometer if a well de¯ned and highly controllable trap is realised. In this thesis results from two experiments that in principle allow the creation of such traps are presented. After reviewing the principles and techniques of atom optics necessary for the understanding of this thesis, a theoretical discussion about the spatial single atom interferometer in a double well potential follows. It is shown that within reasonable limits the system can be reduced to two levels and solved by the Bloch equations. Using the realistic case of a not perfectly symmetric double well potential allows an understanding of the physics behind such an interferometer: how phase is accumulated and how localisation of the atoms leads to the loss of the interferometric signal. Then two experiments are presented. One experiment was newly built up as part of this thesis: it uses a novel hybrid atom chip' with a combination of a magneto-optical ¯lm and current-carrying structures to produce the magnetic trapping potentials. This experiment allowed 5¢108 87Rb atoms to be captured in a magneto-optical trap, where the atom-chip's surface acts as a mirror. The atoms were then transferred into a purely magnetic trap which was created by current carrying structures on the chip. From there on, RF radiation enforced evaporative cooling, so that a quantum degenerate Bose-Einstein condensate of up to 105 atoms was created. It was also shown that the magneto-optical ¯lm is able to hold and trap the atoms. In the second experiment atoms are trapped in the spatially varying inten- sity of light of 1.03 ¹m wavelength. This experiment used an existing set-up as a basis and was modi¯ed and improved for this new project. This experiment starts with 109 87Rb atoms in a 6-beam magneto-optical trap. After examining and optimising the loading process, 1:5 ¢ 105 atoms could be loaded directly from the Magneto-optical trap into the optical dipole potential of two crossed laser beams at 1.03 ¹m. Evaporative cooling was demonstrated though the phase transition to quantum degeneracy was not reached.
A Sagnac atom interferometer can be constructed using a Bose–Einstein condensate trapped in a cylindrically symmetric harmonic potential. Using the Bragg interaction with a set of laser beams, the atoms can be launched into circular orbits, with two counterpropagating interferometers allowing many sources of common-mode noise to be excluded. In a perfectly symmetric and harmonic potential, the interferometer output would depend only on the rotation rate of the apparatus. However, deviations from the ideal case can lead to spurious phase shifts. These phase shifts have been theoretically analyzed for anharmonic perturbations up to quartic in the confining potential, as well as angular deviations of the laser beams, timing deviations of the laser pulses, and motional excitations of the initial condensate. Analytical and numerical results show the leading effects of the perturbations to be second order. The scaling of the phase shifts with the number of orbits and the trap axial frequency ratio are determined. The results indicate that sensitive parameters should be controlled at the 10−5 level to accommodate a rotation sensing accuracy of 10−9 rad/s. The leading-order perturbations are suppressed in the case of perfect cylindrical symmetry, even in the presence of anharmonicity and other errors. An experimental measurement of one of the perturbation terms is presented.