E8: Ultracold titanium

Lab room: Campbell LL104
Lab phone: (510) 664-4841

The realization of quantum gasses of new species has always led to new advances in our understand of quantum phases of matter. Our lab will expand the range of laser cooled and trapped atoms to titanium, along with providing a framework to cooling other transition metals.

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A limitation in ultracold atomic systems arises from the choice of element comprising the quantum degenerate gas. An element’s configuration of electrons dictates the variety and strength of interactions that can be realized in the system, and thus the phases that can be created.

For example, the alkalis and alkali-earth atoms have highly symmetric ground states and consequently a simple spectrum of energy states. Cyclic, laser-cooling transitions exist in these systems, however their simplicity limits their use in simulating condensed matter systems which require complex anisotropic interactions. The symmetry of the ground state leads to atom-light interactions that are independent of both the atomic spin state and the light’s polarization. While strong atom-atom interactions have been demonstrated in long-lived spin-mixed fermionic atomic gases of alkali atoms [1], creating anisotropic light-atom interactions with these atoms [2] require near-resonant light, which significantly reduces experiment lifetimes.

Another type of quantum gases includes the lanthanides such as dysprosium (Dy) and erbium (Er), which are able to create strong anisotropic interactions with far-off-resonance light [3]. However, the atoms’ large magnetic moments (𝜇gs>𝜇B) creates long-range (dipolar) interactions that, while interesting, severely reduce the length of time that atoms in mixtures of spin states will remain trapped [4].

Titanium, and certain other transition metals, present a completely unique atomic system compared to either the alalkis or magnetic 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 (𝜇gs=4/3𝜇B). Titanium has many stable isotopes, ensuring the likelihood of finding favorable collisional parameters. While this ground state is not suitable for laser-cooling directly, a metastable state does have a broad, closed transition (𝛤/2𝜋 = 10.51 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.

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Quantum degenerate gases of titanium will accelerate current scientific endeavors in topological quantum computing, quantum magnetism, and realizing exotic topological phases of matter, but also lead to directions we cannot yet foresee. We are currently building the vacuum chamber and laser system for Doppler-cooling and magneto-optical trapping. Stay tuned :)

 

[1]  W. Ketterle and M. W. Zwierlein. RIVISTA DEL NUOVO CIMENTO, 31:249, 2008.

[2]  Y. J. Lin, et. al. Nature, 471:83, 2011.

[3]  N. Q. Burdick, et. al. Phy. Rev. X, 6:031022, 2016.

[4]  N. Q. Burdick, et. al. Phys. Rev. Lett., 114:023201, 2015.