A Magneto-Optical Trap of Titanium Atoms (2501.05544v1)

Abstract: We realize laser cooling and trapping of titanium (Ti) atoms in a mangeto-optical trap (MOT). While Ti does not possess a transition suitable for laser cooling out of its $\mathrm{3d^24s^2}$ $\mathrm{a^3F}$ ground term, there is such a transition, at an optical wavelength of $\lambda=498\mathrm{nm}$, from the long-lived $\mathrm{3d^3(^4F)4s}$ $\mathrm{a^5F_5}$ metastable state to the $\mathrm{3d^3(^4F)4p}$ $\mathrm{y^5G^o_6}$ excited state. Without the addition of any repumping light, we observe MOTs of metastable $\mathrm{^{46}Ti}$, $\mathrm{^{48}Ti}$, and $\mathrm{^{50}Ti}$, the three stable nuclear-spin-zero bosonic isotopes of Ti. While MOTs can be observed when loaded directly from our Ti sublimation source, optical pumping of ground term atoms to the $\mathrm{a^5F_5}$ state increases the loading rate by a factor of 120, and the steady-state MOT atom number by a factor of 30. At steady state, the MOT of $\mathrm{^{48}Ti}$ holds up to $8.30(26)\times10^5$ atoms at a maximum density of $1.3(4)\times10^{11}\mathrm{cm}^{-3}$ and at a temperature of $90(15)\mathrm{\mu K}$. By measuring the decay of the MOT upon suddenly reducing the loading rate, we place upper bounds on the leakage branching ratio of the cooling transition $(\leq2.5\times 10^{-6})$ and the two-body loss coefficient $(\leq2\times10^{-10}\mathrm{cm}^3\mathrm{s}^{-1})$. Our approach to laser cooling Ti can be applied to other transition metals, enabling a significant expansion of the elements that can be laser cooled.

• The paper presents an innovative method using optical pumping to laser cool titanium atoms, advancing MOT techniques for transition metals.
• Using a 498 nm cycling transition, the approach enhanced loading efficiency by 120-fold and achieved trapping of 8.3×10^5 atoms at temperatures around 90 µK.
• The study reports an exceptionally low leakage branching ratio (≤2.5×10^-6) and negligible two-body loss, highlighting robust performance in quantum gas experimentation.

Magneto-Optical Trapping of Titanium Atoms

The researchers present an advancement in the laser cooling and trapping of transition metal atoms by implementing a magneto-optical trap (MOT) for titanium (Ti) atoms. The work addresses the challenge of laser cooling for transition metals, which historically have been difficult due to the lack of suitable cycling transitions. Through innovative engineering of electronic transitions and optical pumping strategies, they demonstrate a technique that reliably cools and traps Ti atoms, paving the way for expanding MOT technology to other transition metals.

Experimental Setup and Techniques

The authors utilized a direct, yet refined, approach to MOT implementation by leveraging a Ti sublimation source. This source emits Ti atoms, which are optically pumped from their ground state to a metastable state, enabling laser cooling. The Ti was trapped using a notable transition from the 3d$^3$(\textsuperscript{4}F)4s a\textsuperscript{5}F\textsubscript{5} metastable state to the 3d$^3$(\textsuperscript{4}F)4p y\textsuperscript{5}G\textsuperscript{o}\textsubscript{6} excited state, with a wavelength of 498 nm. This metamorphosis effectively realizes a type-I cycling transition that supports conventional MOT operations.

The technique incorporates optical pumping applied to the atomic beam emitted from the thermal sublimator, which increased the loading efficiency as demonstrated by a 120-fold enhancement in loading rate and 30-fold gain in atom number in the MOT.

Key Findings

• Operational Parameters: With efficient optical pumping, approximately 8.3 × 10$^5$ atoms were captured at a density of 1.3 × 10$^11$ cm$^-3$ within the MOT at a temperature of 90(15) $\mu$K. The MOT displayed robust performance despite the intrinsic challenges presented by metastable state populations and transition-metal complexity.
• Efficiency in Transition: The paper notes an upper bound on the leakage branching ratio for the optical transition involved, which was found to be less than or equal to 2.5 × 10$^-6$. This exceptionally low leakage supports the validity of the transition's suitability for sustainable MOT operation on a broader scale.
• Two-Body Loss Constraints: Measurements of MOT dynamics suggest a negligible impact from two-body loss processes, reinforcing the potential robustness of Ti as a candidate for further optical and magnetic trapping investigations.

Implications for Future Research

The implications of these results extend towards the broader adoption of laser cooling techniques in elements that have, until now, remained challenging due to their electronic structure complexities. The paper asserts the possibility of using this experimental approach to extend into other transition metals, potentially leading to new quantum gases exploration. Moreover, the research opens pathways for more refined trap conditions using alternative cooling transitions, such as those offered at longer wavelengths like 1040 nm.

Conclusion

This research exemplifies the applied precision and methodological advancements required to bridge gaps in atomic manipulation techniques, particularly concerning transition metals. Future endeavors may build upon this platform to facilitate new paradigms in quantum technology development, leveraging the novel capabilities of transition metals. Such advancements promise to enhance the understanding and control over quantum interactions in materials previously deemed infeasible for traditional laser cooling and trapping strategies.