ATOMS

When you look at the periodic table, you'll see that there are many captivating elements for constructing neutral atom-based quantum devices. This page is a running document to keep my own thoughts about the elements in one place. I separately also have a page for some fun links and images.

- Kevin

Alkali + Alkali-like Atoms

Lithium

The lightest of the alkalis, lithium has two stable isotopes: a bosonic isotope (lithium-7) and a fermionic isotope (lithium-6). Its light mass coupled with the availability of broad magnetic Feshbach resonances make lithium a fantastic candidate for exploring Bose/Fermi-Hubbard physics in optical lattices. Far right: An image of a lithium MOT (the bright red ball of gas in the middle of the chamber) from my work in the Weld Lab.

Sodium

As someone who is predisposed to high blood pressure, I tend to stay away from sodium. But that doesn't stop other researchers. Sodium has one stable bosonic isotope: sodium-23. The D1 and D2 lines are at ~589 nm, which is a cool looking yellow.

Potassium

Potassium possesses three stable isotopes, one of them being a fermionic isotope. Interestingly, there are only two stable fermionic isotopes among the alkalis: potassium-40 is one and lithium-6 is the other. Potassium also has the smallest ground state hyperfine splittings among the bosonic alkalis. This fact, coupled with the fact that the D1 and D2 lines are close to each other, make potassium a very good candidate for ground state hyperfine clock qubits (mF = 0 to mF' = 0) with long coherence times. One issue with potassium is that its excited state structure on the D2 transition is unresolved (also an issue with lithium).

Rubidium

Rubidium is the veritable workhorse of atomic physics experiments. It has two stable isotopes: rubidium-87 and rubidium-85. The excited state hyperfine structure on the D2 line is also well-separated, giving reasonable cyclicity on laser cooling/imaging transitions. The D2 and D1 lines are at wavelengths where current laser technology can output large amounts of power. Additionally, the lasers needed for exciting rubidium atoms to high-lying Rydberg states are at reasonable wavelengths as well. For example, a combination of 420 nm and 1013 nm light can be used to excite Rb atoms to electronic states with principle quantum numbers around 70. Far right: An image of a Rb MOT (the bright pink ball) in the center of a Faraday cage from my work in the Bernien Lab.

Cesium

Cesium is the time keeper. The SI unit for time, the second, is explicitly defined as:

"The second is the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom."

The hyperfine structure on the D2 transition is also well-resolved, making cesium an excellent candidate for state-resolved fluorescence imaging of ground state qubits. Like rubidium, the lasers needed for exciting cesium atoms to Rydberg states are also at reasonable wavelengths. For example, a two-photon process with 456 nm light and 1060 nm light can be used to coherently couple cesium atoms to electronic states with principle quantum numbers around 70. Far right (top): On the top is a Cs MOT imaged using an infrared-sensitive camera. The MOT is the large white ball in the center of the glass cell. Far right (bottom): Fluorescence images of single Cs atoms trapped in an optical tweezer array from my work in the Bernien Lab. An averaged fluorescence image is on the top and a stochastically loaded image from a a single MOT loading event is on the bottom. The spacing between sites in the array is 10 microns.

Silver

Curiously, there are several other elements in the periodic table that display electronic structure that resemble that of the alkalis. Three such examples are the precious metals: copper, silver, and gold. The terms symbols are: [Ar] 3d10 4s1, [Kr] 4d10 5s1, and [Xe] 4f14 5d10 6s1 for copper, silver, and gold, respectively. Interestingly, these elements prefer to completely fill their outermost d-orbitals rather than having two electrons in the outermost s subshell. On the right is a plot showing the analogous D2 line of silver-109. It also has a narrow-line transition at 330.6 nm with a linewidth of ~ 1 Hz.

Alkaline-Earth + Alkaline-Earth-Like Atoms

Strontium

Like the alkalis, alkaline-earth-like atoms possess strong, broad electronic transitions that can be used for laser cooling and trapping. Unlike the alkalis, alkaline-earth-like atoms also possess a number of narrow-line transitions from the ground state that can be used for enhanced cooling, measurement, and quantum state manipulation. For instance, the world's most precise clocks are made using the 698 nm 1S0–3P0 clock transition in strontium, which has a linewidth of ~ 1 mHz. Strontium has four stable isotopes: three bosonic isotopes with zero nuclear spin and one fermionic isotope with a nuclear spin of 9/2 (strontium-87). The ground state has zero electronic spin, decoupling the electronic spin from interactions with optical tweezers or lattices. However, for quantum information processing purposes, it is nice to have a two-level system in the ground state or in a long-lived meta-stable state of the atom. One can use the fermionic isotopic with nuclear spin 9/2, but extra care must be taken to isolate two suitable levels in this manifold. As a rather unfortunate property of our universe, none of the atoms in the alkaline-earth column of the periodic table have stable isotopes with nuclear spin 1/2, which is what one would want for a clean two-level qubit.

Magic tweezer wavelengths: 813.4 nm (3P0 magic), 515 nm (3P1 magic)

Rydberg wavelengths: 317 nm (5s5p 3P0 – 5s 47s 3S1 )

Right: on the bottom is an image of a strontium MOT (small blue ball) taken from my time in the Weld Lab.

Ytterbium

This is where ytterbium comes into the picture. Ytterbium has seven stable isotopes. Importantly, one of these isotopes, ytterbium-171, has a nuclear spin of 1/2, providing a clean, long-lived nuclear spin qubit with long-coherence times. This property, coupled with electronic transitions that are reasonably addressed with current laser technology, make ytterbium a fantastic candidate for quantum information processing applications. Interestingly, ytterbium is actually a lanthanide. It is rather curious that no "true" alkaline-earth atom has a stable isotope with nuclear spin 1/2.

Magic tweezer wavelengths: 759.35 nm (3P0 magic), 486.78 nm (3P1 magic), 483 nm (3P1 magic, mF = +/- 3/2)

Rydberg wavelengths: 308 nm (5s5p 3P0 – 6s 74s 3S1 )

Cadmium

There are several other elements in the periodic table that display electronic structure similar to that of alkaline-earths. For example, atoms at the end of the d-block. One such atom is cadmium, which possess two isotopes with a nuclear spin of 1/2: cadmium-111 and cadmium-113. It also has a narrow 1S0–3P0 clock transition that has promising applications for optical lattice clocks with decreased sensitivity to blackbody radiation [*]. Unfortunately, the laser wavelengths and powers needed to drive these electronic transitions are a bit more difficult to manage than those needed for strontium and ytterbium.

Magic tweezer wavelengths: ~420 nm (3P0 magic)

Mercury

Mercury is also an alkaline-earth-like atom that has an isotope with nuclear spin 1/2: mercury-199. The main electronic transitions from the ground state are in the ultraviolet, which is a bit difficult to manage on a large-scale with current laser technology.

Other lanthanides

Erbium

There is a lot of excitement to explore lanthanides other than ytterbium for neutral atom array technologies. Two such atoms are erbium and dysprosium. On the right are five energy levels in erbium that can be addressed with laser technology. In addition to possessing a strong line at 401 nm for broad line cooling, erbium has a number of narrow lines for enhanced cooling or quantum state manipulation. One interesting feature of erbium is that it possesses a narrow-line telecom transition from the ground state which could be used to make telecom-compatible quantum network nodes.

References

General energy levels and transitions:

Kramida, A., Ralchenko, Yu., Reader, J., and NIST ASD Team (2022). NIST Atomic Spectra Database (ver. 5.10), [Online]. Available: https://physics.nist.gov/asd [2023, August 1]. National Institute of Standards and Technology, Gaithersburg, MD. DOI: https://doi.org/10.18434/T4W30F

Lithium structure:

Gehm, Michael E. , Properties of 6Li, see: https://jet.physics.ncsu.edu/techdocs/pdf/PropertiesOfLi.pdf

Potassium structure:

Tiecke, T. G. , Properties of Potassium, see: https://www.tobiastiecke.nl/archive/PotassiumProperties.pdf

Sodium, Rubidium, Cesium structure:

D. A. Steck

Sodium D line data, see: https://steck.us/alkalidata/sodiumnumbers.pdf

Rubidium D line data, see: https://steck.us/alkalidata/rubidium87numbers.pdf and https://steck.us/alkalidata/rubidium85numbers.pdf

Cesium D line data, see: https://steck.us/alkalidata/cesiumnumbers.pdf

Silver structure:

G. Uhlenberg, J. Dirscherl, and H. Walther. Magneto-optical trapping of silver atoms. Phys. Rev. A 62, 063404 (2000)

Cadmium structure:

[*] A. Yamaguchi, M. S. Safronova, K. Gibble, and H. Katori. Narrow-line Cooling and Determination of the Magic Wavelength of Cd. Phys. Rev. Lett. 123, 113201 (2019)

Mercury structure:

Liu Hong-Li et al. Magneto-optical trap for neutral mercury atoms. Chinese Phys. B 22 043701 (2013)

Ytterbium structure:

Shuo Ma, Alex P. Burgers, Genyue Liu, Jack Wilson, Bichen Zhang, and Jeff D. Thompson. Universal Gate Operations on Nuclear Spin Qubits in an Optical Tweezer Array of 171Yb Atoms. Phys. Rev. X 12, 021028 (2022)

M.A. Norcia et al. Mid-circuit qubit measurement and rearrangement in a 171Yb atomic array. Phys. Rev. X 13, 041034 (2023)

Joanna W. Lis, Aruku Senoo, William F. McGrew, Felix Rönchen, Alec Jenkins, Adam M. Kaufman. Mid-circuit operations using the omg-architecture in neutral atom arrays. Phys. Rev. X 13, 041035 (2023)

Erbium/Dysprosium structure:

H. Y. Ban, M. Jacka, J. L. Hanssen, J. Reader, and J. J. McClelland. Laser cooling transitions in atomic erbium. Optics Express. 13, Issue 8, pp. 3185-3195 (2005)

A. Patscheider, B. Yang, G. Natale, D. Petter, L. Chomaz, M. J. Mark, G. Hovhannesyan, M. Lepers, and F. Ferlaino. Observation of a narrow inner-shell orbital transition in atomic erbium at 1299 nm. Phys. Rev. Research 3, 033256 (2021)

Damien Bloch, Britton Hofer, Sam R. Cohen, Antoine Browaeys, Igor Ferrier-Barbut. Trapping and imaging single dysprosium atoms in optical tweezer arrays. Phys. Rev. Lett. 131, 203401 (2023)

Banner Image: A photo I took of the inside of a Stable Lasers Systems ultra-low expansion (ULE) optical reference cavity in the Bernien Lab.

Level diagrams: All level diagrams on this page were made by me in Illustrator using the above references for guidance.

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