Overview
In our lab we are working on direct laser cooling of calcium monofluoride (CaF) molecules. The complex internal level structure of molecules may make them seem a daunting prospect to control. However, here at Durham we are building an experiment to produce ultracold, controlled CaF molecules.
Laser cooling molecule experiments all start in the same way, creating the molecules. For this we are building a cryogenic buffer gas source, shown in figure to the right. The source consists of a calcium metal target which we ablate using a pulsed Nd:YAG laser, we flow sulfur hexafluoride gas into the vicinity of the newly created Ca ions which leads to the formation of CaF molecules. This all happens inside a copper cell mounted on a 4 Kelvin cyrocooler, into which helium gas, also at 4 K, is injected and collides with the CaF, sympathetically cooling it. The molecules then leave the cell with a forward velocity of around 150 m/s. This is far too fast to be captured in a magneto-optical trap (MOT), and so the molecules must next be decelerated.
We are currently working on chirped laser slowing, where we counterpropagate a laser at 531 nm and scan (or chirp) the frequency to keep the laser on resonance with the molecules as they decelerate and experience a changing Doppler shift. The next step of the experiment will be to load the molecules into a MOT. This work is supported by UKRI Future Leaders Fellowship MR/X033430/1.
Team members
 CaF team Feb 2025 (AJM, AB, RH, BH, HJW) | Dr. Hannah J. Williams (she/her) -- PI Dr. Bethan Humphreys (she/her) -- PDRA Mr Archie Baldock (he/him) -- PhD student Miss Rebecca Hedley (she/her) -- PhD student |
Former members
Dr. Alex J. Matthies (they/them) -- PDRAMr Tom Philo (he/him) -- MSci student
Mr Keelan Sloan (he/him) -- MSci student
Mr Andrew Elwood (he/him) -- MSci student
News
2026
July: Bethan and Becca attend the QSMol kick-off meeting. Nicole joins the team for a summer internship, welcome Nicole!June: Archie presents a poster at ICAP in Wuhan and the ultracold molecules satellite meeting in Hong Kong. Alex leaves the group to start a postdoc position in Gothenburg - good luck and thank you!
May: We finish the Zeeman-Sisyphus project, sadly we saw no deceleration. April: Our proposal paper on near-deterministic loading of tweezer arrays is on ArXiv: https://arxiv.org/abs/2604.22406.
2025
September: Hannah returns to work. Bethan and Hannah attend the EPSRC Quantum Technologies Future Leaders Event.August: Our paper DiPolMol-Py: A Python package for calculations for 2Σ ground-state molecules has been published here.
July: Archie presents a poster at ECAMP15 and Becca presents a poster at YAO, both in Innsbruck.
June: Tom graduates, congratulations and best of luck in the future! Bethan presents a poster at ICOLS2025 on the island of Elba and Alex presents a poster at the Workshop on Ultracold Molecules in Warsaw.
May: Bethan passes her viva! Congratulations, and welcome back as a PDRA Dr. Humphreys!!
April: Hannah begins maternity leave!
March: Becca attends PG Women in Physics . We submit our first paper! DiPolMol-Py: A Python package for calculations for 2Σ ground-state molecules, and Bethan submits her PhD thesis.
January: The whole team head to Imperial College for the first UK laser cooling molecules workshop.
2024
October: Rebecca joins the group for her PhD, and Tom starts his Master's project. Welcome to the team both! Alex spends three weeks visiting cold molecule labs in the USA.September: Alex and Hannah attend CCMI near Vienna, Alex presents a poster and Hannah gives an invited talk.
July: We host the Dipolar Quantum Matter ICAP satellite meeting, which is a resounding success! Archie presents a poster at the ICAP summer school at Oxford university and Bethan presents a poster at ICAP
June: Alex presents a poster at EGAS in Granada. Keelan and Andrew both graduate, congratulations and good luck in your future endeavours!
April: We see CaF molecules in the lab for the first time!
2023
December: Hannah is awarded a UKRI Future Leaders Fellowship for the project Molecules for Quantum Simulation to start June 2024.November: Bethan gives her first academic talk at the Northern Quantum Meeting IX in Sheffield.
October: The team is growing rapidly! Archie Baldock joins the team as a PhD student. We also have two MSci students joining: Keelan Sloan working on background free imaging of CaF and Andrew Elwood building a cooled, leader-follower laser system.
September: Dr. Alex Matthies joins the team as a PDRA, welcome Alex.
July: James, Yuchao and Mattew all graduate from Durham University, congratulations all! Keelan Sloan joins the group for a summer placement to help build our cryogenic buffer gas source, welcome to the team Keelan.
June: Bethan presents her first poster at EGAS in Strasbourg.
January: Hannah is awarded a New Investigator Award from EPSRC to test a Zeeman-Sisyphus decelerator for calcium fluoride molecules to run April 2023-September 2025.
2022
October: Three MSci students join the group: James Crilly (co-supervised by Dr. Carty works on simulating the Zeeman-Sisyphus decelerator), Matthew Page & Yuchao Liu (co-supervised by Prof. Cornish work on tweezer simulations and creation using a spatial light modulator).September: The lab refurbishment is complete!
July: Bethan passes her 9-month progression. Congratulations!
February: Bethan attends the Introductory Course on Ultracold Quantum Gases in Innsbruck.
January: Work starts on converting office space into our lab.