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A dual species MOT of Yb and Cs

Kirsteen Louisa Butler

Published Jan 1, 2014• 1 citation
OpenAlex

Abstract

This thesis describes the design and construction of a new apparatus to laser cool and trap Yb and Cs atoms with the ultimate aim of creating ultracold molecules with both an electric and magnetic dipole moment, which are of great interest in a range of fields. The Yb and Cs atomic beams are first generated and overlapped in a dual species oven. A collimated atomic beam of the two species is formed by the use of an array of capillary tubes at the exit of the oven. At this stage the atoms have an average velocity of 311m/s or 264m/s for Yb and Cs respectively, therefore it is necessary to reduce their velocity before they can be trapped in a magneto-optical trap (MOT). This initial stage of slowing is carried out with a Zeeman slower. Due to their atomic properties, Yb and Cs atoms are unable to be slowed by the same magnetic field profile therefore they cannot be loaded simultaneously, however, the Zeeman slower can load the atoms into a MOT sequentially. Once their velocities have been reduced to approximately 48m/s (10m/s) the Cs (Yb) atoms can be captured in a MOT. The laser systems for cooling Yb and Cs are also presented. Laser cooling of Cs is achieved on the D2 transition at 852.3nm whereas Yb can either be cooled on the 1S0 to 1P1 or 1S0 to 3P1 transitions at 398.9nm or 555.8nm respectively. Due to the relative linewidths of these transitions (2π×28.0MHz and 2π × 182.2kHz), Zeeman slowing is performed for Yb on the 1S0 to 1P1 transition and magneto-optical trapping on the 1S0 to 3P1 transition. A Cs MOT with 1 × 10^8 atoms and an Yb MOT with the order of 10^8 atoms on the narrow 556nm transition are demonstrated. The mixture can be sequentially loaded into a dual species MOT, paving the way for many further experiments exploring this novel mixture.

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This thesis describes the design and construction of a new apparatus to laser cool and trap Yb and Cs atoms with the ultimate aim of creating ultracold molecules with both an electric and magnetic dipole moment, which are of great interest in a range of fields. The Yb and Cs atomic beams are first generated and overlapped in a dual species oven. A collimated atomic beam of the two species is formed by the use of an array of capillary tubes at the exit of the oven. At this stage the atoms have an average velocity of 311m/s or 264m/s for Yb and Cs respectively, therefore it is necessary to reduce their velocity before they can be trapped in a magneto-optical trap (MOT). This initial stage of slowing is carried out with a Zeeman slower. Due to their atomic properties, Yb and Cs atoms are unable to be slowed by the same magnetic field profile therefore they cannot be loaded simultaneously, however, the Zeeman slower can load the atoms into a MOT sequentially. Once their velocities have been reduced to approximately 48m/s (10m/s) the Cs (Yb) atoms can be captured in a MOT. The laser systems for cooling Yb and Cs are also presented. Laser cooling of Cs is achieved on the D2 transition at 852.3nm whereas Yb can either be cooled on the 1S0 to 1P1 or 1S0 to 3P1 transitions at 398.9nm or 555.8nm respectively. Due to the relative linewidths of these transitions (2π×28.0MHz and 2π × 182.2kHz), Zeeman slowing is performed for Yb on the 1S0 to 1P1 transition and magneto-optical trapping on the 1S0 to 3P1 transition. A Cs MOT with 1 × 10^8 atoms and an Yb MOT with the order of 10^8 atoms on the narrow 556nm transition are demonstrated. The mixture can be sequentially loaded into a dual species MOT, paving the way for many further experiments exploring this novel mixture.
This thesis presents progress toward the production of ultracold CsYb molecules. To this end, an apparatus capable of producing magneto optical traps of Yb and Cs was designed, built and tested. Both atoms are produced in a dual species oven and both slowed to low speeds by a single Zeeman slower. From the Zeeman slower atoms are captured in a dual-species magneto-optical trap. To cool caesium the 852 nm D2 transition is addressed by two lasers for cooling and repump. For ytterbium the 399 nm 1S0 ⇒ 1P1 transition is addressed for the Zeeman slower and the 556 nm 1S0 ⇒ 3P1 transition is addressed for the magneto-optical trap. The 399 nm light is produced by two homebuilt diode lasers in an injection-seeding setup, which can produce up to 100 mW. The 556 nm light is produced from a commercial frequency doubled fiber laser, which can produce up to 260 mW. The Zeeman slower is characterised experimentally for both Cs and Yb, and the results compared to those of a numerical simulation of the slower for Yb. The velocity distribution exiting the slower is very sensitive to the exact magnetic field profile, the laser power and detuning of the laser light. The number of atoms loaded into the magneto-optical trap was investigated as a function of the magnetic field gradient, the laser power and the laser detuning. The capture velocity of the Yb MOT is small because the linewidth of the MOT transition is narrow, and so we investigated the influence of broadening the laser linewidth by adding multiple finely-spaced sidebands to the laser light. After optimisation the caesium MOT trapped 5.5 ×10^8 atoms at 125 ± 4 μK. The ytterbium MOT trapped 4.7 ×10^9 atoms at 81 ± 2 μK. Lastly we demonstrate that both MOTs can be produced in the same vacuum chamber simultaneously.
We describe an apparatus designed to trap and cool a Yb and Cs mixture. The apparatus consists of a dual species effusive oven source, dual species Zeeman slower, magneto-optical traps in a single ultra-high vacuum science chamber, and the associated laser systems. The dual species Zeeman slower is used to load sequentially the two species into their respective traps. Its design is flexible and may be adapted for other experiments with different mixtures of atomic species. The apparatus provides excellent optical access and can apply large magnetic bias fields to the trapped atoms. The apparatus regularly produces 10(8) Cs atoms at 13.3 μK in an optical molasses, and 10(9) (174)Y b atoms cooled to 22 μK in a narrowband magneto-optical trap.
This thesis presents the development of an experimental apparatus designed to investigate the ultracold collisional properties for mixtures of Cs and Yb, with a long-term view to the creation of ultracold CsYb molecules via indirect cooling methods. The unpaired electron spin that is inherent to molecules of this form gives rise to a magnetic dipole moment in addition to a ground state electric dipole moment. This enables extra control over molecular interactions and should enable the experimental simulation of spin lattice models. We focus on the implementation of a system designed to controllably laser cool and optically trap Yb. The first step in this system is the production of a magneto-optical trap (MOT) on the triplet 1S0 to 3P1 transition of Yb. With careful control over the cooling beam detunings and power, gravitational-assisted Doppler cooling allows samples of Yb to be prepared at 22 uK. This regime of enhanced Doppler cooling is investigated and proves to be a crucial step to ensuring good transfer of cold Yb to optical traps. The construction and characterisation of single and crossed beam optical dipole traps for Yb are discussed. The single beam optical trap has been used to verify a model for the optical trapping of Yb in its ground state. This trap has also been utilised as a tool for the measurement of the light shift on the 1S0 to 3P1 transition at a wavelength of 1070~nm. In the main experimental sequence, Yb atoms are loaded from the magneto-optical trap into the crossed optical dipole trap, allowing evaporative cooling ramps to quantum degeneracy to be performed. This highly-reproducible system typically forms Bose-Einstein condensates with 2 x 10^5 174Yb atoms. This thesis additionally reports on the progress made towards measurements of the interspecies scattering length for 133Cs and Yb isotopes. We present two approaches that are being developed in tandem: rethermalisation in a conservative trap, and two-photon photoassociation. Progress towards rethermalisation measurements has focussed on developing systems for the efficient transfer of Cs to an optical trap. For photoassociative measurements, a laser system has been developed and tested by producing one-photon photoassociation spectra of Cs2.
We describe the design, construction, and operation of a versatile dual-species Zeeman slower for both Cs and Yb, which is easily adaptable for use with other alkali metals and alkaline earths. With the aid of analytic models and numerical simulation of decelerator action, we highlight several real-world problems affecting the performance of a slower and discuss effective solutions. To capture Yb into a magneto-optical trap (MOT), we use the broad (1)S0 to (1)P1 transition at 399 nm for the slower and the narrow (1)S0 to (3)P1 intercombination line at 556 nm for the MOT. The Cs MOT and slower both use the D2 line (6(2)S1/2 to 6(2)P3/2) at 852 nm. The slower can be switched between loading Yb or Cs in under 0.1 s. We demonstrate that within a few seconds the Zeeman slower loads more than 10(9) Yb atoms and 10(8) Cs atoms into their respective MOTs. These are ideal starting numbers for further experiments on ultracold mixtures and molecules.
This thesis describes the advances made towards a dual-species magneto-optical trap (MOT) of Li and Rb for use in photoassociation spectroscopy, Feshbach resonance studies, and, as long-term aspirations, the formation of ultracold heteronuclear polar molecules. The initial discussion will focus on a brief theoretical overview of laser cooling and trapping and the production of ultracold molecules from a cold atom source. Subsequently, details of the experimental system, including those pertaining to the required laser light, the vacuum chamber, and the computer control system will be presented. Finally, preliminary optimization and characterization measurements showing the performance of a single species Li MOT are introduced. These measurements demonstrated the loading of over 8 x 107 Li atoms directly into a MOT without the need for a Zeeman slower.
We demonstrate a dual magneto-optical trap (MOT) of 109Ag^{109}\mathrm{Ag}109Ag and 39K^{39}\mathrm{K}39K. For silver, a decreasing-field Zeeman slower loads a MOT of $1.5\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at a temperature of 0.74(5) mK, with laser cooling occurring primarily on the D2{D}_{2}D2​ line of $4{d}^{10}5s\phantom{\rule{0.28em}{0ex}}^{2}S_{1/2}\ensuremath{\rightarrow}5p\phantom{\rule{0.28em}{0ex}}^{2}P_{3/2}$ at 328 nm. We create a Ag ``dark spot MOT,'' where shelving the atoms in a dark state enhances the captured atom number by a factor of 2 and the lifetime by a factor of 4. For potassium, we obtain $2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ trapped atoms, and further cooling on the D1{D}_{1}D1​ transition via gray molasses results in a cloud of $1.2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at $7(1)\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{K}$. We observe evidence of photoionization loss of the K MOT in the presence of Ag laser-cooling light, necessitating sequential rather than simultaneous loading for the two species. Our results on Ag point to simple and general laser cooling strategies for other coinage metals (Au, Cu). Furthermore, this work lays the foundation for the production of alkali-metal--coinage-metal degenerate quantum mixtures and highly polar molecules.