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arXiv:0706.1608 · Physical Review A

Magneto-optical trapping of cadmium

Kathy-Anne Brickman, M.-S. Chang, M. Acton, Andrew Chew, Dzmitry Matsukevich, P. C. Haljan, Vanderlei Salvador Bagnato, Christopher R. Monroe

Published Oct 11, 2007• 51 citations
arXivHTMLPDF

Abstract

We report the laser cooling and confinement of Cd atoms in a magneto-optical trap and characterize the loading process from the background Cd vapor. The trapping laser drives the $^{1}S_{0}\ensuremath{\rightarrow}^{1}P_{1}$ transition at $229\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in this two-electron atom and also photoionizes atoms directly from the $^{1}P_{1}$ state. This photoionization overwhelms the other loss mechanisms and allows a direct measurement of the photoionization cross section, which we measure to be $2(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}$ from the $^{1}P_{1}$ state. When combined with nearby laser-cooled and trapped ${\mathrm{Cd}}^{+}$ ions, this apparatus could facilitate studies in ultracold interactions between atoms and ions.

DOI
10.1103/physreva.76.043411

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We report the laser cooling and confinement of Cd atoms in a magneto-optical trap and characterize the loading process from the background Cd vapor. The trapping laser drives the 1S0\ensuremath→1P1^{1}S_{0}\ensuremath{\rightarrow}^{1}P_{1}1S0​\ensuremath→1P1​ transition at 229nm229\phantom{\rule{0.3em}{0ex}}\mathrm{nm}229nm in this two-electron atom and also photoionizes atoms directly from the 1P1^{1}P_{1}1P1​ state. This photoionization overwhelms the other loss mechanisms and allows a direct measurement of the photoionization cross section, which we measure to be 2(1)\ifmmode×\else\texttimes\fi10\ensuremath−16cm22(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}2(1)\ifmmode×\else\texttimes\fi10\ensuremath−16cm2 from the 1P1^{1}P_{1}1P1​ state. When combined with nearby laser-cooled and trapped Cd+{\mathrm{Cd}}^{+}Cd+ ions, this apparatus could facilitate studies in ultracold interactions between atoms and ions.
Atomic cadmium ions are loaded into radiofrequency ion traps by photoionization of atoms in a cadmium vapor with ultrafast laser pulses. The photoionization is driven through an intermediate atomic resonance with a frequency-quadrupled mode-locked Ti:sapphire laser that produces pulses of either $100\text{\ensuremath{-}}\mathrm{fs}$ or $1\text{\ensuremath{-}}\mathrm{ps}$ duration at a central wavelength of 229nm229\phantom{\rule{0.3em}{0ex}}\mathrm{nm}229nm. The large bandwidth of the pulses photoionizes all velocity classes of the Cd vapor, resulting in a high loading efficiency compared to previous ion trap loading techniques. Measured loading rates are compared with a simple theoretical model, and we conclude that this technique can potentially ionize every atom traversing the laser beam within the trapping volume. This may allow the operation of ion traps with lower levels of background pressures and less trap electrode surface contamination. The technique and laser system reported here should be applicable to loading most laser-cooled ion species.
Laser cooling and trapping of the heavy alkaline-earth-metal element barium has been achieved based on the strong $6{s}^{2}\text{ }{^{1}S}_{0}\text{\ensuremath{-}}6s6p\text{ }{^{1}P}_{1}$ transition. The excited state decays to a large fraction into metastable DDD states. Two schemes were implemented where three additional laser-driven transitions provide closed cooling cycles. This results in a fraction of 50(20)% of the trapped atoms in one of the metastable states. A total efficiency of $0.4(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ for slowing a thermal atomic beam and capturing atoms into a magneto-optical trap was obtained. Trap lifetimes of more than 1.5 s were observed. They are shortened at high laser intensities by three photon photoionization losses. The developed scheme can be transferred to other systems with large leakage from the cooling transition, such as Ra which is interesting for sensitive fundamental symmetry research.
Over the past decade, the field of trapped ion quantum computing has emerged as one of the leaders in quantum information processing due the level of manipulation available and the long coherence times possible in the system. As this thesis will demonstrate, all of the necessary building blocks for a quantum computer have been exhibited in ion traps and small scale quantum algorithms have been implemented. In this trapped ion system, quantum bits consist of the first order magnetic field insensitive ground state hyperfine levels of 111^{111}111Cd+^++. The qubits are manipulated via resonant and off-resonant coherent laser interactions. We experimentally realize Grover's quantum search algorithm over a 4 element database with n=2 trapped 111^{111}111Cd+^++ ion qubits. One of the four states is marked, and with a single query it is recovered, on average, with 60% probability. This exceeds the performance of any possible classical search, which can only succeed with 50% probability following a single query. The algorithm consists of two Molmer-Sorensen entangling gates, that utilize bichromatic stimulated Raman transitions to create a spin dependent force, paired with several single-qubit rotations and near-perfect qubit measurements. The spectral arrangement of the Raman beams is tailored to suppress phase noise accumulation between gates. This suppression is critical for reliably performing consecutive operations during the algorithm. Additionally, this thesis discusses the possibility of combining trapped ions with trapped neutral atoms for the purpose studying ultra-cold charge exchange interactions. It may be possible to conceal quantum information, initially prepared in an ionic qubit, inside a pure nuclear spin qubit for the purpose of transportation and storage. As a first step, we present the laser-cooling and confinement of Cd atoms in a magneto-optical trap, and characterize the loading process from the background Cd vapor. The trapping laser drives the 1S0^{1}S_{0}1S0​~rightarrowrightarrowrightarrow~1P1^{1}P_{1}1P1​ transition at 229 nm in this two valence electron atom and also photoionizes atoms directly from the 1P1^{1}P_{1}1P1​ state. This photoionization dominates other loss mechanisms and allows a direct measurement of the photoionization cross section.
We demonstrate the simultaneous magneto-optical trapping (MOT) of Rb and Sr and examine the characteristic loss of Rb in the MOT due to photoionization by the cooling laser for Sr. The photoionization cross section of Rb in the 5P3/25P_{3/2}5P3/2​ state at 461 nm is determined to be 1.2×10−171.2\times10^{-17}1.2×10−17 cm2^22. It is important to consider this loss rate to realize a sufficiently large number of trapped Rb atoms to achieve a quantum degenerate mixture of Rb and Sr.
We report the measurement of one-body loss rates for magnetically trapped metastable europium atoms and the study of their loss mechanism. The loss of atoms observed in a magneto-optical trap is not fully understood because of the indivisibility of the loss regarding optical pumpings due to the presence of cooling laser beams. We magnetically trap the atoms by directly loading from the magneto-optical trap and observe almost identical one-body loss rates of approximately 2.6 s−12.6\,\mathrm{s^{-1}}2.6s−1 for two isotopes: 151Eu\mathrm{{}^{151}Eu}151Eu and 153Eu\mathrm{{}^{153}Eu}153Eu. Our rate-equation-based model, combined with loss rate measurements carried out with repumpers, shows that blackbody radiation at room temperature drives E1 transitions and induces the observed losses.
We report narrow-line laser cooling and trapping of strontium atoms down to the photon recoil temperature. 88Sr{}^{88}\mathrm{Sr}88Sr atoms precooled by the broad $^{1}S_{0}\ensuremath{-}^{1}P_{1}$ transition at 461 nm were further cooled in a magneto-optical trap using the spin-forbidden transition $^{1}S_{0}\ensuremath{-}^{3}P_{1}$ at 689 nm. We have thus obtained an atomic sample with a density over ${10}^{12}\mathrm{cm}{}^{\ensuremath{-}3}$ and a minimum temperature of 400 nK, corresponding to a maximum phase space density of ${10}^{\ensuremath{-}2}$ which is 3 orders of magnitude larger than the value that has been obtained by magneto-optical traps to date. This scheme provides us an opportunity and system to study quantum statistical properties of degenerate fermions as well as bosons.