Progress on the realization of an experimental setup for the simultaneous creation of quantum degenerate samples of fermionic /sup 40/K and bosonic /sup 87/Rb is presented. The apparatus is based on a double MOT design with a 2D source MOT and a 3D collection MOT both acting on both species. After laser cooling selective forced microwave evaporative cooling of /sup 87/Rb on the hyperfine transition is planned in a magnetic Ioffe-Pritchard trap. The fermionic /sup 40/K component will be sympathetically cooled by the rubidium atoms without additional loss of particles until quantum degeneracy is reached. A high number of fermions is expected by using isotope enriched /sup 40/K dispensers for feeding the 2D source MOT.
Progress on the realization of an experimental setup for the simultaneous creation of quantum degenerate samples of fermionic /sup 40/K and bosonic /sup 87/Rb is presented. The apparatus is based on a double MOT design with a 2D source MOT and a 3D collection MOT both acting on both species. After laser cooling selective forced microwave evaporative cooling of /sup 87/Rb on the hyperfine transition is planned in a magnetic Ioffe-Pritchard trap. The fermionic /sup 40/K component will be sympathetically cooled by the rubidium atoms without additional loss of particles until quantum degeneracy is reached. A high number of fermions is expected by using isotope enriched /sup 40/K dispensers for feeding the 2D source MOT.
This thesis deals with dilute fermionic and bosonic quantum gases in the nK temperature regime.In the work presented here, the first quantum-degenerate mixture of two different fermionic atomic species and the first triple-degenerate Fermi-Fermi-Bose mixture were produced.The quantum-degenerate mixtures were realized using sympathetic cooling of the fermionic species 6 Li and 40 K by an evaporatively cooled gas of bosonic 87 Rb atoms in a magnetic trap.The apparatus, which was designed and built from scratch in this thesis work, provides a very versatile platform for a broad range of experiments.As the first important step in the production of the quantum-degenerate three-species mixture, simultaneous magneto-optical trapping of 6 Li, 40 K, and 87 Rb was achieved, thereby demonstrating the first three-species magneto-optical trap ("triple MOT") and the first two-fermion MOT.The triple MOT is loaded with lithium from a Zeeman slower and with potassium and rubidium from the background vapor that is maintained by atomic vapor dispensers.For this purpose, dispensers for potassium enriched in the isotope 40 K were produced.The triple MOT was characterized and studied with respect to light-assisted interspecies losses.Furthermore, a sequence combining a compressed MOT and a temporal dark MOT is presented that, in spite of the differing requirements of the three species, allows us to achieve favorable starting conditions for further cooling in the QUIC-type magnetic trap.A magnetic transport system is used to transfer the precooled atomic clouds from the MOT position into the QUIC trap.The transport scheme was adapted to the specific requirements of the three-species mixture, in particular to the temperature of laser-cooled lithium, which is high in comparison to other species.The quantum-degenerate regime is reached by evaporative and sympathetic cooling in the QUIC trap.Species-selective evaporation of rubidium is achieved by driving a 87 Rb hyperfine transition to an untrapped state.In order to avoid undesired atom losses and heating due to spin-exchange collisions, the atoms are prepared in the maximally polarized internal ground states.Careful state cleaning during the cooling process was found crucial to attain quantum degeneracy.Since evaporative and sympathetic cooling both rely on energy transfer by elastic collisions between atoms, the efficiency of the cooling process depends on the relevant elastic scattering cross sections.The 87 Rb-87 Rb and 40 K-87 Rb scattering cross sections are quite favorable for this purpose.The 6 Li-87 Rb scattering cross section, however, was unknown at the beginning of the project and was later found to be comparatively small, making sympathetic cooling of 6 Li by 87 Rb rather challenging.In this thesis work, an experimental sequence was developed that nevertheless allows the production of a quantum-degenerate 6 Li gas with large atom number in this mixture.Furthermore, it is shown that in the three-species mixture, the efficiency of the cooling process for 6 Li is significantly increased by the presence of 40 K through catalytic cooling.The quantum-degenerate Fermi-Fermi and Fermi-Fermi-Bose mixtures realized in this thesis work serve as a starting point for a broad range of possible future experiments, including the creation of heteronuclear Fermi-Fermi dimers and the investigation of the BEC-BCS cross-over regime.In this context, the possibilities opened by the mass difference and the differing internal structures of the two fermionic species are of particular interest.v Zusammenfassung Die vorliegende Arbeit befaßt sich mit verdünnten fermionischen und bosonischen Quantengasen im nK-Temperaturbereich. Im Rahmen der Arbeit wurden sowohl die erste quantenentartete Mischung zweier verschiedener fermionischer Atomspezies als auch die erste dreifach entartete Fermi-Fermi-Bose-Mischung erzeugt.Die quantenentarteten Mischungen wurden durch sympathetisches Kühlen der fermionischen Spezies 6 Li and 40 K mit einem mittels Verdampfungskühlung aktiv gekühlten Gas bosonischer 87 Rb-Atome in einer Magnetfalle realisiert.Die Apparatur, die hierfür in dieser Arbeit entworfen und von Grund auf aufgebaut wurde, bietet eine äußerst vielseitige Plattform für ein breites Spektrum an Experimenten.Als erster wichtiger Schritt für die Produktion der quantenentarteten Drei-Spezies-Mischung konnten 6 Li, 40 K und 87 Rb simultan magneto-optisch gefangen werden.Dies stellt die erste Realisierung einer magneto-optischen Falle für drei Spezies ("Dreifach-MOT") und einer MOT für zwei fermionische Spezies dar.Die Dreifach-MOT wird mit Lithium aus einem Zeeman-Abbremser und mit Rubidium und Kalium aus dem Hintergrund-Gas geladen, das durch Atomgas-Dispenser aufrechterhalten wird.Zu diesem Zweck wurden Dispenser mit im Isotop 40 K angereichertem Kalium hergestellt.Die Dreifach-MOT wurde charakterisiert und bezüglich lichtunterstützter Interspezies-Verluste studiert.Desweiteren wird eine aus einer komprimierten MOT und einer zeitlichen Dunkel-MOT kombinierte Sequenz vorgestellt, die es ermöglicht, trotz der sich unterscheidenden Anforderungen der drei Atomsorten günstige Ausgangsbedingungen für das folgende Kühlen in der QUIC-Magnetfalle zu erzielen.Für den Transfer der vorgekühlten Atome von der MOT-Position in die QUIC-Falle wird ein magnetisches Transport-System verwendet.Das Transport-Schema wurde an die besonderen Anforderungen der Drei-Spezies-Mischung angepaßt, insbesondere auch an die im Vergleich zu anderen Spezies hohe Temperatur von lasergekühltem Lithium.Das quantenentartete Regime wird durch Verdampfungskühlung und sympathetisches Kühlen in der QUIC-Falle erreicht.Speziesselektive Verdampfungskühlung von Rubidium wird durch Treiben eines 87 Rb-Hyperfein-Übergangs in einen ungefangenen Zustand erzielt.Um unerwünschte Atomzahlverluste und Heizen durch Spinaustausch-Stöße zu verhindern, sind die Atome in den maximal polarisierten Grundzuständen präpariert.Eine sorgfältige Zustandsreinigung während des Kühlprozesses hat sich als entscheidend zum Erreichen der Quantenentartung erwiesen.Da sowohl Verdampfungskühlung als auch sympathetisches Kühlen auf Energieübertragung durch elastische Stöße zwischen den Atomen beruhen, hängt die Effizienz des Kühlprozesses von den relevanten elastischen Streuquerschnitten ab.Die Streuquerschnitte für 87 Rb-87 Rb-und 40 K-87 Rb-Stöße sind hierfür recht günstig.Der 6 Li-87 Rb-Streuquerschnitt hingegen war zu Beginn des Projektes noch unbekannt und stellte sich später als vergleichsweise klein heraus, so dass sympathetisches Kühlen von 6 Li durch 87 Rb erheblich erschwert ist.In dieser Arbeit konnte jedoch eine experimentelle Sequenz entwickelt werden, die in dieser Mischung trotzdem die Erzeugung eines quantenentarteten 6 Li-Gases mit großer Atomzahl gestattet.Desweiteren wird gezeigt, dass die Kühleffizienz für 6 Li in der Drei-Spezies-Mischung durch die Anwesenheit von 40 K aufgrund von katalytischem Kühlen signifikant erhöht ist.Die im Rahmen dieser Arbeit erzeugten quantenentarteten Fermi-Fermi-und Fermi-Fermi-Bose-Mischungen dienen als Startpunkt für ein breites Spektrum möglicher zukünftiger Experimente, wie beispielsweise der Erzeugung heteronuklearer Fermi-Fermi-Dimere oder der Erforschung des BEC-BCS-Übergangs.Besonders interessant sind dabei die Möglichkeiten, die sich durch die Massendifferenz und die unterschiedlichen internen Strukturen der zwei fermionischen Spezies ergeben.viii
This thesis reports on experiments with quantum degenerate atomic mixtures and molecular gases at ultracold temperatures.The work describes the first realization of a quantum degenerate Fermi-Fermi mixture of two different species with unequal masses.In addition, the first quantum degenerate three-species mixture is realized.Furthermore, the first heteronuclear bosonic molecules with temperatures close to quantum degeneracy are created from a two-species mixture.Within this work a new and very versatile experimental platform to study quantum degenerate two-species Fermi mixtures is presented.The experimental concept relies on sympathetic cooling of two fermionic species ( 40 K and 6 Li) by a large bosonic gas ( 87 Rb).It is shown that large atom numbers and reliable operation are guaranteed by careful choice of the experimental components and parameters, which is essential to deal with the complexity of such an experimental platform with three atomic species.The first important milestone towards quantum degeneracy is realized by simultaneous trapping 87 Rb, 40 K and 6 Li in a magneto-optical trap.This marks the first realization of magneto-optical trapping of two fermionic species and also of three species.To achieve quantum degeneracy, different experimental challenges and difficulties of the three species with very different initial temperatures, scattering cross sections and masses were overcome.A combined compressed MOT and temporal dark MOT phase, a careful state cleaning process during the cooling process, species selective evaporative cooling of rubidium and removing of high energetic lithium atoms turn out to be essential for the successful realization of a quantum degenerate Fermi-Fermi-Bose mixture.Furthermore, at the end of the sympathetic cooling process, the cooling efficiency of lithium is improved by catalytic cooling through potassium.A quantum degenerate Fermi-Fermi mixture can be realized in the strongly interacting regime at a s-wave Feshbach resonance.By an adiabatic magnetic field sweep across the Feshbach resonance ultracold bosonic heteronuclear molecules are created with high efficiencies of up to 50 %.The associated number of molecules are up to 4 × 10 4 molecules, which is the largest number of heteronuclear molecules produced so far.Furthermore, close to resonance an increased molecular lifetime of more than 100 ms is observed.Therefore, this is the first system that may be used to explore many-body physics of a heteronuclear mixture in the strongly interacting regime across a Feshbach resonance.The heteronuclear Fermi mixture adds the mass ratio and the different internal structure as new parameters to quantum degenerate Fermi gases.The molecular cloud being close to quantum degeneracy marks the first starting point for the realization of a heteronuclear molecular BEC and to investigate the BEC-BCS crossover with unequal masses.Moreover, the molecules can be transferred into the rovibrational ground state to create a polar BEC with an anisotropic, long-range interaction.
We report on the first experimental setup based on a 2D-/3D-magneto-optical trap (MOT) scheme to create both Bose-Einstein condensates and degenerate Fermi gases of several ytterbium isotopes. Our setup does not require a Zeeman slower and offers the flexibility to simultaneously produce ultracold samples of other atomic species. Furthermore, the extraordinary optical access favors future experiments in optical lattices. A 2D-MOT on the strong (1)S0 → (1)P1 transition captures ytterbium directly from a dispenser of atoms and loads a 3D-MOT on the narrow (1)S0 → (3)P1 intercombination transition. Subsequently, atoms are transferred to a crossed optical dipole trap and cooled evaporatively to quantum degeneracy.
We report a compact experimental setup for producing a quantum degenerate mixture of Bose 23Na and Fermi 40K gases. The atoms are collected in dual dark magneto–optical traps (MOT) with species timesharing loading to reduce the light-induced loss, and then further cooled using the gray molasses technique on the D 2 line for 23Na and D 1 line for 40K. The microwave evaporation cooling is used to cool 23Na in | F = 2,mF = 2〉 in an optically plugged magnetic trap, meanwhile, 40K in | F = 9/2,mF = 9/2〉 is sympathetically cooled. Then the mixture is loaded into a large volume optical dipole trap where 23Na atoms are immediately transferred to |1,1〉 for further effective cooling to avoid the strong three-body loss between 23Na atoms in |2,2〉 and 40K atoms in |9/2,9/2〉. At the end of the evaporation in optical trap, a degenerate Fermi gas of 40K with 1.9 × 105 atoms at T/TF = 0.5 in the |9/2,9/2〉 hyperfine state coexists with a Bose–Einstein condensate (BEC) of 23Na with 8 × 104 atoms in the |1,1〉 hyperfine state at 300 nK. We also can produce the two species mixture with the tunable population imbalance by adjusting the 23Na magneto–optical trap loading time.
We investigate sympathetic cooling fermions 40 K by evaporatively cooling bosonic 87 Rb atoms in a magnetic trap with microwave and radio frequency induced evaporations in detail. The mixture of bosonic and fermionic atoms is prepared in their polarized spin states | F = 9/2, m F = 9/2〉 for 40 K and | F = 2, m F = 2〉 for 87 Rb, which is trapped in Quadrupole—Ioffe—Configuration trap. Comparing microwave with radio frequency evaporatively cooling bosonic 87 Rb atoms with sympathetically cooling Fermi gas 40 K, we find that the presence of rubidium atoms in the |2, 1〉 Zeeman states, which are generated in the evaporative process, gives rise to a significant loss of 40 K due to inelastic collisions. Thus, the rubidium atoms populated in the |2, 1〉 Zeeman states should be removed in order to effectively perform sympathetically cooling 40 K with the evaporatively cooled 87 Rb atoms.