We present a new quantum gas apparatus for ultracold mixtures of K and Cs atoms and ultracold samples of KCs ground-state molecules. We demonstrate the apparatus’ capabilities by producing Bose–Einstein condensates of 39K and 133Cs in a manner that will eventually allow sequential condensation within one experimental cycle, precise sample overlap and magnetic association of atoms into KCs molecules. The condensates are created independently without relying on sympathetic cooling. Our approach is universal and applicable to other species combinations when the two species show dramatically different behavior in terms of loss mechanisms and post laser cooling temperatures, i.e. species combinations that make parallel generation of quantum degenerate samples challenging. We give an outlook over the next experiments involving e.g. sample mixing, molecule formation and transport into a science chamber for high-resolution spatial imaging of novel quantum-many body phases based on K–Cs.
We present a new quantum gas apparatus for ultracold mixtures of K and Cs atoms and ultracold samples of KCs ground-state molecules. We demonstrate the apparatus’ capabilities by producing Bose–Einstein condensates of 39K and 133Cs in a manner that will eventually allow sequential condensation within one experimental cycle, precise sample overlap and magnetic association of atoms into KCs molecules. The condensates are created independently without relying on sympathetic cooling. Our approach is universal and applicable to other species combinations when the two species show dramatically different behavior in terms of loss mechanisms and post laser cooling temperatures, i.e. species combinations that make parallel generation of quantum degenerate samples challenging. We give an outlook over the next experiments involving e.g. sample mixing, molecule formation and transport into a science chamber for high-resolution spatial imaging of novel quantum-many body phases based on K–Cs.
Ultracold atomic gases have proven to be a versatile tool for the study of many-body quantum physics thanks to the high degree of control that they offer. However, interactions between neutral atoms are usually short-ranged and isotropic, which limits their applicability as a simulator of real condensed matter systems. One of the most common methods of introducing stronger interactions into an ultracold gas is associating pairs of atoms of two different elements into molecules. Such molecules possess a body-fixed electric dipole moment, which can be addressed by an external electric field or microwave radiation to engineer long-ranged, tunable dipolar interactions. In addition to constituting an analogue quantum simulator, ultracold dipolar molecules show potential as a platform for digital quantum computation, precision measurements, and the study of quantum chemistry. The main result presented in this thesis is the first successful synthesis of ultracold 39K133Cs molecules in their vibrational and rotational ground state. Using a novel simultaneous cooling scheme for potassium and caesium, our team has been able to produce mixtures that are cold enough for efficient magnetoassociation into weakly bound molecules to take place. By performing high-resolution laser spectroscopy of these molecules, I have identified a two-photon pathway to the ground state via an exceptionally narrow intermediate excited state. I was then able to perform Stimulated Raman Adiabatic Passage (STIRAP) along that pathway with one-way efficiencies up to 71%, producing trapped samples of up to 3500 ground-state molecules at temperatures of 1 µK. The lifetime of these samples is currently limited by a near-universal two-body loss process, a further study of which could shed light on similar loss mechanisms in other molecular species. I have also carried out preliminary rotational spectroscopy, which paves the way towards using KCs molecules as a controlled interacting spin system and a refinement of their hyperfine coupling constants. The thesis ends with a detailed outline of further steps that should be taken to improve the efficiency of STIRAP, as well as the population and coherence lifetimes in KCs samples. It is followed by a list of suggested experiments that could be carried out using our system after it undergoes the described technical upgrades. Some of these experiments are directly inspired by the results I have obtained during my six-month research stay in the KRb laboratory at JILA.
We report the creation of an ultracold gas of bosonic K 39 Cs 133 molecules. We first demonstrate a cooling strategy relying on sympathetic cooling of Cs 133 to produce an ultracold mixture. From this mixture, weakly bound molecules are formed using a Feshbach resonance at 361.7 G. The molecular gas contains 7.6 ( 10 ) × 10 3 molecules with a lifetime of about 130 ms, limited by two-body decay. We perform Feshbach spectroscopy to observe several new interspecies resonances and characterize the bound state used for magnetoassociation. Finally, we fit the combined results to obtain improved K-Cs interaction potentials. This provides a good starting point for the creation of ultracold samples of ground-state K 39 Cs 133 molecules.
Abstract We report a new apparatus for the study of two-species quantum degenerate mixture of 41 K and 6 Li atoms. We develop and combine several advanced cooling techniques to achieve both a large atom number and high phase space density of the two-species atom clouds. Furthermore, we build a high efficiency two-species magnetic transport system to transfer atom clouds from the 3D magneto-optical-trap chamber to a full glass science chamber of an extreme high vacuum environment and good optical access. We perform a forced radio-frequency evaporative cooling for 41 K atoms while the 6 Li atoms are sympathetically cooled in an optically plugged magnetic trap. Finally, we achieve the simultaneous quantum degeneracy for the 41 K and 6 Li atoms. The Bose–Einstein condensate of 41 K has 1.4 × 10 5 atoms with a condensate fraction of about 62%, while the degenerate Fermi gas of 6 Li has a total atom number of 5.4 × 10 5 at 0.25 Fermi temperature.
An apparatus for ultracold Na-40/41K mixtures toward ground-state molecule production
We present an apparatus for producing ultracold Na- 40 K and Na- 41 K mixtures as a starting point for the formation of fermionic and bosonic ground-state NaK molecules. Sodium and potassium atoms are first loaded into a magneto-optical trap and transferred to an optically plugged magnetic trap, where the mixture undergoes sympathetic cooling via radio-frequency evaporation of Na. A key feature of the apparatus is its ability to switch between loading fermionic 40 K and bosonic 41 K by toggling three acousto-optic modulators. After further sympathetic cooling in an optical dipole trap, we obtain quantum-degenerate Bose–Fermi Na- 40 K and Bose–Bose Na- 41 K mixtures. This apparatus provides a robust starting point for creating ultracold Bose and Fermi gases of ground-state NaK molecules, opening pathways to explore strongly interacting dipolar quantum matter.
This thesis reports the formation of a dual-species Bose-Einstein condensate of 87Rb and 133Cs in the same trapping potential. Quantum degenerate mixtures exhibit rich physics inaccessible to single species experiments and provide an ideal starting point for the creation of ultracold dipolar molecules. These molecules offer a wealth of new research avenues including precision metrology, quantum simulation and computation. The experimental method exploits the efficient sympathetic cooling of 133Cs via elastic collisions with 87Rb, initially in a magnetic quadrupole trap and subsequently in a levitated optical trap. Evaporative cooling in the dipole trap must compete against a high interspecies three-body inelastic collision rate \mbox{∼10−25−10−26~cm6/s}. The two condensates each contain up to \mbox{2×104} atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the 87Rb during the cooling leads to the creation of single-species 133Cs condensates of up to \mbox{6×104} atoms. In addition this thesis reports the observation of an interspecies Feshbach resonance at 181.7(5)~G and the creation of a pure sample of Cs2 molecules via magneto-association on the 4(g)4 resonance at 19.8~G. These results represent important steps towards the creation of ultracold polar RbCs molecules.
The field of ultracold matter has developed rapidly over the course of the past twenty to thirty years. One outstanding achievement has been the realisation of Bose-Einstein condensation (BEC) only 23 years ago. Many other fascinating observations of quantum phenomena have been made at an incredibly fast pace using ultracold atomic samples with contact force interactions as a testbed. Due to the rapid successes of all these experiments on atomic ensembles, researchers began to aim for more elaborate inter-particle interactions. A possible additional one is the dipole-dipole interaction (DDI), the long-range character of which stands out in comparison to the contact interactions. Moreover, DDI is anisotropic and the possibility to tune the direction of the dipoles in the experiment as well as the interaction strength promises the possibility to study a plethora of new quantum phenomena. In recent years, several experiments using different combinations of alkali atoms to create ground-state hetero-nuclear molecules in the ultracold regime have been set up, following the pioneering work on KRb molecules. Of all possible combinations of two alkali atoms, NaK combines the advantages of a high induced electric dipole moment of 2.72 Debye, chemical stability of the ground-state molecules, the possibility to realise bosonic as well as fermionic molecules and a large knowledge base for cooling and trapping of the two atomic species. This thesis reports on the development and construction of an experiment apparatus for the production of ultracold bosonic dipolar ground state 23Na39K molecules. This includes the setup of an ultra-high vacuum (UHV) system, several laser light sources, microwave (MW) and radio frequency (RF) antennas and electronics to control the various components of the experiment. The system pre-cools the atomic samples of 23Na and 39K and loads them into a dual-species three-dimensional magneto-optical trap (3D MOT). After a transfer to a magnetic quadrupole trap, the mixture is cooled by forced MW evaporation until three-body losses limit dual-species operation at high densities and zero magnetic field. Using the pure optical trapping potential of a crossed optical dipole trap (cODT) and RF- state-transfer, the scattering properties of the bosonic mixture of 23Na+39K are investigated in extensive atom loss measurements for a magnetic field range from 0 to 750 G. Several Feshbach resonances, zero crossings of the interspecies scattering length and inelastic loss features in many different scattering channels are identified. The results of this study are used to refine the molecular potentials of NaK and to produce a dual-species quantum-degenerate mixture of two BECs in the state (f = 1, mf = −1) of 23Na + (f = 1, mf = −1) of 39K. The measurements and refined molecular potentials will considerably aid in the future realisation of 23Na39K molecules in their absolute ground state.