We discuss two experiments that can be performed using a cloud of laser-cooled and trapped atoms, namely Bose-Einstein condensation (BEC) and search for a permanent Electric Dipole Moment (EDM). BEC can be observed in Rb atoms in a magnetic trap by using forced evaporative cooling to continuously lower the temperature below the condensation limit. The cloud is cooled by preferentially ejecting the hottest atoms from a magnetic trap. The magnetic trap is loaded with laser-cooled atoms from a magneto-optic trap. The EDM experiment can be performed with a laser-cooled cloud of Yb atoms. The atoms are spin polarized and the precession of the spin is measured in the presence of a strong electric field applied perpendicular to the spin direction. The use of laser-cooled atoms should greatly enhance the sensitivity of the experiment.
We discuss two experiments that can be performed using a cloud of laser-cooled and trapped atoms, namely Bose-Einstein condensation (BEC) and search for a permanent Electric Dipole Moment (EDM). BEC can be observed in Rb atoms in a magnetic trap by using forced evaporative cooling to continuously lower the temperature below the condensation limit. The cloud is cooled by preferentially ejecting the hottest atoms from a magnetic trap. The magnetic trap is loaded with laser-cooled atoms from a magneto-optic trap. The EDM experiment can be performed with a laser-cooled cloud of Yb atoms. The atoms are spin polarized and the precession of the spin is measured in the presence of a strong electric field applied perpendicular to the spin direction. The use of laser-cooled atoms should greatly enhance the sensitivity of the experiment.
Summary form only given.We have established an experimental and theoretical program focused on understanding photon atom interactions in condensates with the aim of probing the properties of condensates as well as testing our models of the interactions themselves. With a combination of laser and evaporative cooling, we are routinely creating million atom Bose-Einstein condensates of sodium atoms in the newly designed 4D magnet. Our experimental setup incorporates a candlestick atomic beam source, which provides for recirculation of uncollimated sodium atoms, The laser cooling step involves a zero-crossing Zeeman slower, magneto-optic trap, and polarization gradient cooling. The laser-cooled atom cloud is loaded into the 4D magnetic trap and adiabatically compressed to high density and an evaporative cooling process is initiated. Using a RF magnetic resonance technique, hot atoms are ejected through magnetic spin flips. After formation of the condensate in the tightly confining trap, we manipulate the condensate by adiabatically changing the trapping potential and through interaction with photons. We have developed a technique for probing the condensates directly inside the trap using near-resonant absorption imaging. This imaging technique gives high sensitivity to details of the condensate wavefunction and to its surface structure. Images of pure condensates are compared to calculations of the condensate wavefunction based on a Hartree mean field description of the two-body interaction between condensate atoms.
In 1925, Einstein predicted the condensation of bosons into the ground state of the system for low (but finite) temperatures. Several phenomena, including superfluidity and superconductivity have been associated with Bose-Einstein condensation, but these systems interact strongly with their environment and pure Bose-Einstein condensation could not be established. It took 70 years, in which time the laser was discovered, and laser cooling techniques to manipulate atoms in a dilute atomic gas, before Bose-Einstein condensation in dilute atomic gases could be demonstrated in 1995. In the first condensation experiments, BECs were created in a magnetic trap. Since in a magnetic trap not all mF states of the atom can be trapped simultaneously, thereby limiting the number of experiments that can be done, other ways of trapping and generating BECs were sought and found. In 2001, the first all-optical BEC was made, where the dipole force was used to trap atoms in the crossing of two far red detuned laser beams. In an optical dipole trap not only atoms in different internal states can be trapped, but also different atomic species simultaneously. In this thesis, the formation of an all-optical Bose-Einstein condensate with rubidium atoms is presented. Conventional all-optical BECs are usually created in high power CO2 laser dipole traps, or have complicated laser cooling schemes and complex dipole trap setups. In our simple and straightforward setup, we load rubidium atoms from a magneto-optical trap into a crossed optical dipole trap created by a single frequency Yb:YAG laser with a wavelength at 1030 nm. The small wavelength allows for a small diffraction limit, and permits us to use standard optical materials, thus making the experimental setup cost effective. Other attempts to achieve Bose-Einstein condensation in a multi-mode (frequency) fiber laser at 1064 nm failed, because the atom loss was quite high. It is assumed that the multi-mode character of the fiber laser induces Raman transitions in rubidium atoms, thereby heating them. We can trap about ∼ 5E7 atoms in a single beam dipole trap out of ∼ 5E9 atoms trapped in theMOT, and ∼ 350,000 atoms can be trapped in a crossed beam dipole trap due to the smaller trap volume. 70% of the atoms in the dipole trap is optically pumped into one mF state. Quantum degeneracy is reached by evaporatively cooling the atoms in the crossed dipole trap by ramping down the laser power with three linear ramps. We can independently change the power of each beam by an AOM. This allows us to use one beam as an atom waveguide for future experiments. After evaporation, we typically have about 10,000 atoms at a temperature below the critical temperature. We have proved Bose-Einstein condensation by using the anisotropic expansion of a quantum degenerate gas trapped in an anisotropic potential. The aspect ratio of our atom cloud changed during a time of flight from 0.7 to 1.2 in 10 ms, thus proving that we have reached quantum degeneracy. We have about 5,000 condensed atoms in our optical dipole trap at a temperature less than 100 nK. The remaining atoms are thermal. Bose-Einstein condensation is obtained within 8 s, and we can repeat the experiment every 30 s. It should be mentioned that the Bose-Einstein experiment was moved from the ”Leibniz Universität Hannover” to the ”Technische Universität Darmstadt”, and had to be completely rebuilt. All-optical Bose-Einstein condensation was reached within one year after the move. Our Bose-Einstein condensation setup presents an ideal starting point for using our condensates in combination with miniaturized atom optical setups based on our novel microfabricated optical elements. With our microlenses, we can create a number of possible dipole trap configurations, such as the dipole trap array or the cylindrical microlens array. Using microlenses in miniaturized atom optical setups opens a completely new field of coherent atom optics. Also because the tight confinement of the microtraps allows us to load a 3D BEC, a 1D BEC, or a Tonks-Girardeau gas in the micropotentials depending on the density.
Experimental techniques to produce and observe a Bose-Einstein condensate of rubidium atoms are presented. The atoms are first optically cooled and trapped in an ultra-high vacuum (-10-11 torr) glass cell using a double magneto-optical trap, and then transferred to a “cloverleaf” magnetic trap. Rf-induced evaporation is performed to further cool the magnetically trapped atoms below the phase transition of Bose-Einstein condensation. The velocity distribution (inferred by absorption imaging) of the cooled atomic cloud clearly shows the expected bi-modal structure characteristic of a condensate
Summary form only given. Bose-Einstein condensates (BEC) are generally produced by evaporative cooling of laser cooled atomic samples in magnetic traps. Though magnetic traps are indispensable for the production of a BEC, they pose restrictions on the possible studies with a BEC. Previous experiments of our group have demonstrated that it is possible to trap a BEC in the circular focus of a far-detuned infrared laser beam. This first realization of an optical dipole trap (ODT) for BEC was used to prepare and investigate spinor condensates of Na atoms in the F=1 hyperfine manifold. However, the initial peak density in this ODT after loading from the magnetic trap reached 10/sup 15/ atoms/cm/sup 3/, leading to rapid losses due to three-body collisions. To realize an ODT capable of storing large condensates for a long time, we have used a laser beam with an elliptical beam profile. The optical trap is loaded by superimposing the light field onto the magnetic trap and then slowly turning off the magnetic fields. The transfer efficiency is close to 100%, and thus more than 10/sup 7/ Bose-condensed atoms can be loaded into the ODT.
Presents work on the realization of Bose-Einstein condensates (BEC) in optical and electro-magnetic traps. We have done some theoretical and experimental work on the project. We have proposed an optical funnel or a hollow beam, which are produced from a short micron-sized hollow optical fiber or a set-up of lenses. The cold atoms extracted from an magneto-optical trap experience effective Sisyphus cooling in the dark hollow beam. We calculate the potential barriers for atomic guiding in the dark hollow beam, and analyze the atomic losses during the guiding process. Inside the hollow beam atoms experience an efficient Sisyphus cooling and repumping-beam induced geometric cooling. We have estimated the total loss rate of the cold atoms, and it shows that an ultracold and dense Rb atomic sample with a 3D temperature of /spl sim/1 K can be obtained and the appearance of an optically-trapped Bose-Einstein condensation may be possible in this optical trap. We have also made a proposal of a micro-wave electro-magnetic trap, which is working at the frequency which is very far from the optical transition of the cold atoms. The trapping force comes from the interaction between the electro-magnetic induced magnetic dipole moment with the electro-magnetic field. Theoretical calculation shows that the force can be used to trap the cold atoms in the trap.
Summary form only given. Recently, we have created a Bose condensate of /sup 87/Rb atoms directly in an optical trap formed by tightly focused laser beams. Following initial loading from a laser cooled gas, evaporative cooling through the BEC transition is achieved by simply lowering the depth of the optical trap. Our success is due in part to a high initial phase space density realized in the loading of our optical dipole trap and in part to the tight confinement of the atoms that permits rapid evaporative cooling to the BEC transition in 2 s.