With any ultracold atomic system, a particular atom's electronic configuration dictates the variety and strength of interactions that can be realized in the system, and thus the phases that can be created. Titanium is unlike all previous laser cooled atoms and it's properties will allow us to probe the physics on particles with anisotropic interactions in ways other atoms cannot. These interactions are needed to study novel phenomena such as the fraction quantum Hall effect and topological materials in 2D systems.

To begin it is worth consdiering what can be done with the workhorse atoms of atomic physics, the alkalis and alkali-earth atoms. They all have highly symmetric ground states and consequently a simple spectrum of energy states. Cyclic transitions exist in the ground states of these systems, which makes cooling and trapping them easy. However, the symmetry of the ground state leads to atom-light interactions that are largely independent of both the atomic spin state and the light’s polarization, limiting the strength of anisotropic interactions that can be generated. Creating anisotropic light-atom interactions with these "simple" atoms requires near-resonant light[1], which significantly reduces experiment lifetimes through heating of the atoms.

The other major group of atoms that have been cooled to the ultracold regime are the so-called magnetic atoms: dysprosium (Dy) holmium (Ho), and erbium (Er), which are able to create strong anisotropic interactions with far-off-resonance light [2]. However, the atoms’ large magnetic moments (𝜇_gs>𝜇_B) creates long-range (dipolar) interactions that, while interesting, severely reduce the length of time that atoms in mixtures of spin states will remain trapped [3]. Without the ability to study spin mixtures, many interesting quantum phases remain unable to be realized using these aroms.

Titanium, and certain other transition metals, present a new atomic system compared to either of the previously studied atoms. A quantum degenerate gas of titanium atomic gas will allow for the realization of anisotropic light-atom interactions with far-off-resonance light in long-lived mixtures of spin states not limited by long-range dipolar interactions. This is possible because titanium’s lowest energy electronic configuration, [Ar]3d ²4s², yields a ground state a³F₂ with non-zero orbital angular momentum (L=3), yet a small magnetic moment (𝜇_gs=4/3𝜇_B). Titanium has many stable isotopes, ensuring the likelihood of finding favorable atom-atom collisions. These properties make titanium an ideal experimental platform for studying many body quantum systems with anisotropic interactions.

While this ground state is not suitable for laser-cooling directly, a metastable state does have a broad, closed transition (λ = 498 nm, 𝛤/2𝜋 = 12.1 MHz) that is ideal for laser-cooling. Using this transition, we plan to laser-cool and trap titanium atoms via traditional means: spin-flip Zeeman slower addressing atoms from a hot metal vapor and further cooling and trapping in a magneto-optical trap (MOT), allowing us to reach temperatures of approximately 250 𝜇K.