CsYb: Quantum degenerate mixtures and magnetic molecules

In the CsYb experiment, we trap and cool atoms of Caesium and Ytterbium to the quantum degenerate regime. We create dual-degenerate mixtures of Bose-Einstein condensates and study their interactions and novel quantum phases.

We are also working towards assembling Caesium and Ytterbium atoms into CsYb molecules - the combination of an alkali-metal like Cs and a closed-shell atom like Yb.

Quantum degenerate mixtures: Beyond mean-field interactions

The very different atomic structure of Cs and Yb makes it easy to independently manipulate them. The large number of stable Yb isotopes allows us to tailor their interactions and quantum statistics to suit our experiments.

By using a two species mixture we can achieve a balance of intra- and interspecies interactions that allows us to observe higher order interaction terms, driven by quantum fluctuations.

This way we’ll be able to change the character of our ultra dilute quantum gas mixture to that of a liquid – instead of expanding freely, the mixture will form self-bound quantum droplets.

Magnetic molecules

Unlike bi-alkali molecules produced in our other experiments, CsYb molecules have an unpaired electron. This means their ground state not only has an electric dipole moment, but also a magnetic dipole moment, giving us an additional handle to control. This makes them a promising experimental platform for quantum simulation of lattice spin models as well as quantum information.

We have recently observed magnetic Feshbach resonances, the first step towards assembling Cs and Yb atoms into molecules by magnetoassociation. We are also researching alternative association mechanisms like photoassociation and mergoassociation.


In summer 2023, we upgraded our vacuum apparatus to include a glass cell. Ultracold Cs and Yb atoms will be transferred into this cell from the stainless-steel chamber where previous experiments were performed by optical transport.

Improved optical access in the glass cell will allow us to finely control the experimental properties of our atomic mixtures and perform high-resolution imaging of our atom clouds.

Join us!

We are looking to recruit a PhD student in 2024. For more information email s.l.cornish@durham.ac.uk.


As part of our quantum degenerate mixtures research, we actively collaborate with the Quantum Matter Research Group at Newcastle University, and the Vortices in Superfluids group at the University of Strathclyde.

In our work on ultracold collisions and towards molecule production we work closely with the group of Jeremy Hutson at the Department of Chemistry

Lab publications


[9] Observation of magnetic Feshbach resonances between Cs and 173Yb
Tobias Franzen*, Alexander Guttridge*, Kali E. Wilson*, Jack Segal, Matthew D. Frye, Jeremy M. Hutson, and Simon L. Cornish
Phys. Rev. Research 4, 043072 (2022)

[8] Dynamics of a degenerate Cs-Yb mixture with attractive interspecies interactions
Kali E. Wilson*, Alexander Guttridge*, I-Kang Liu, Jack Segal, Thomas P. Billam, Nick G. Parker, N. P. Proukakis, and Simon L. Cornish
Phys. Rev. Research 3, 033096 (2021)

[7] Quantum degenerate mixtures of Cs and Yb
Kali E. Wilson*, Alexander Guttridge*, Jack Segal, and Simon L. Cornish
Phys. Rev. A 103, 033306 (2021)

[6] Two-photon photoassociation spectroscopy of CsYb. Ground-state interaction potential and interspecies scattering lengths
A. Guttridge, Matthew D. Frye, B. C. Yang, Jeremy M. Hutson, and Simon L. Cornish
Phys. Rev. A 98, 022707 (2018)

[5] Production of ultracold CsYb molecules by photoassociation
Alexander Guttridge, Stephen A. Hopkins, Matthew D. Frye, John J. McFerran, Jeremy M. Hutson, and Simon L. Cornish
Phys. Rev. A 97, 063414 (2018)

[4] Interspecies thermalization in an ultracold mixture of Cs and Yb in an optical trap
A. Guttridge, S. A. Hopkins, S. L. Kemp, Matthew D. Frye, Jeremy M. Hutson, and Simon L. Cornish
Phys. Rev. A 96, 012704 (2017)

[3] Direct loading of a large Yb MOT on the 1S0 to 3P1 transition
A. Guttridge, S. A. Hopkins, S. L. Kemp, D. Boddy, R. Freytag, M. P. A. Jones, M. R. Tarbutt, E. A. Hinds, and S. L. Cornish
_ J. Phys. B At. Mol. Opt. Phys_ 49, 145006 (2016)

[2] A versatile dual-species Zeeman slower for caesium and ytterbium
S. A. Hopkins, K. Butler, A. Guttridge, S. Kemp, R. Freytag, E. A. Hinds, M. R. Tarbutt, and S. L. Cornish
_ Rev. Sci. Instrum._ 87, 043109 (2016)

[1] Production and characterization of a dual species magneto-optical trap of cesium and ytterbium
S. L. Kemp, K. L. Butler, R. Freytag, S. A. Hopkins, E. A. Hinds, M. R. Tarbutt, and S. L. Cornish
_ Rev. Sci. Instrum._ 87, 023105 (2016)


PhD theses

Jack Segal: Ultracold and quantum degenerate mixtures of Cs and Yb (2023)

Alexander Guttridge: Photoassociation of Ultracold CsYb Molecules and Determination of Interspecies Scattering Lengths (2018)

Stefan Kemp: Laser cooling and trapping of Ytterbium (2017)

Kirsteen Butler: A dual species MOT of Yb and Cs (2014)