Characteristics of a magneto-optical trap of molecules
H.J. Williams, S. Truppe, M. Hambach, L. Caldwell, N. Fitch, E.A. Hinds, B. Sauer, M.R. Tarbutt
New J. Phys. 19 113035 (2017)

Synopsis: Magneto-optical traps (MOTs) for molecules are new, so a thorough characterisation of their properties is called for. This paper presents a detailed investigation of the properties of a MOT of CaF molecules. We first study how molecules load into the MOT from a decelerated molecular beam. Then we measure how the number of molecules, the photon scattering rate, the oscillation frequency, damping constant, temperature, cloud size and lifetime depend on the key parameters of the MOT, especially the intensity and the detuning of the light. By comparing our results to analytical and numerical models we shed light on the mechanisms at work in molecule MOTs. We hope this paper will be a useful resource to all groups wishing to build and characterize their own molecular MOTs.
Contributes to objectives:
2 –  The MOT is the first step in cooling below the Doppler limit

9 – A chip-based MOT may be a good way to load molecules into microscopic chip traps
11 – The MOT is the starting point for loading single molecules into tweezer traps

A buffer gas beam source for short, intense and slow molecular pulses
S. Truppe, M. Hambach, S. Skoff, N. Bulleid, J. Bumby, R.J. Hendricks, E.A. Hinds, B. Sauer, M.R. Tarbutt
Journal of Modern Optics, 65:3 246-254 (2018)

Synopsis: Experiments with directly-cooled molecules usually begin with a source. This paper describes a pulsed source of molecules with characteristics that are ideal for many experiments – the pulses have high flux, low speed, low temperature and short duration. We make CaF molecules by laser ablation of a Ca target in the presence of SF6 gas. The molecules are caught in a flow of 4K helium, which cools them and produces a directed beam. We present the design of the source, give practical details about how to build it, and characterize its performance.

Contributes to objectives: 2-  The source makes the CaF, ready for laser cooling


Characterizing Feshbach resonances in ultracold scattering calculations
M.D. Frye, J.M. Hutson
Phys. Rev. A 96, 042705 (2017)

Hyperfine structure of alkali-metal diatomic molecules
J. Aldegunde, J.M. Hutson
Phys. Rev. A 96, 042506 (2017)

Inelastic losses in radio-frequency-dressed traps for ultracold atoms
D.J. Owens, J.M. Hutson
Phys. Rev. A 96, 042707

Atomic clock measurements of quantum scattering phase shifts spanning Feshbach resonances at ultralow fields
A. Bennett, K. Gibble, S. Kokkelmans, J.M. Hutson
Phys. Rev. Lett. 119, 113401 (2017)

Molecules cooled below the Doppler limit
S. Truppe, H.J. Williams, M. Hambach, L. Caldwell, N. Fitch, E.A. Hinds, B. Sauer, M.R. Tarbutt
Nature Physics 13 1173-1176 (2017)

Synopsis: The magneto-optical trap (MOT) is the workhorse of experiments with ultracold atoms. A MOT uses a combination of laser beams and a magnetic field to trap and cool atoms. The main cooling mechanism is Doppler cooling, which is effective when the laser light is detuned to the red side of the atomic transition, but cannot cool below a certain temperature limit, known as the Doppler limit.  A molecule MOT, first demonstrated in Yale using SrF molecules, is an ideal starting point for many applications of ultracold molecules. In this paper, we demonstrate the word’s second molecule MOT, using CaF molecules. We capture about 10,000 molecules, cool them to a few millikelvin, and store them for about 100 ms. We then demonstrate that a second cooling mechanism, sub-Doppler cooling, is effective when the light is blue-detuned and the magnetic field is turned off. Using this mechanism, we cool molecules below the Doppler limit for the first time, reaching a temperature of 50 microkelvin.
Contributes to objectives:
2-  We have cooled CaF molecules to sub-Doppler temperatures

11 – Loading into a tweezer trap requires low temperature and dissipation, which we demonstrate

ac Stark effect in ultracold polar 87Rb133Cs molecules
P. D. Gregory, J. A. Blackmore, J. Aldegunde, J. M. Hutson, and S. L. Cornish
Phys. Rev. A 96, 021402(R) (2017)

Synopsis: To interrogate ultracold molecules for a long time it is necessary to confine them in a trap. In the case of RbCs molecules where there is no magnetic moment, this trap has to be formed using far-off resonance laser beams in a so-called optical trap. In this paper, we investigate the effect of such trapping light on the internal rotational and hyperfine states of ultracold RbCs molecules. We use high-precision microwave spectroscopy to measure the differential ac Stark shifts between hyperfine states in the ground and first excited rotational levels of the molecule that result from the interaction with the trapping light. We demonstrate through both experiment and theory that coupling between neighbouring hyperfine states manifests in rich structure with many avoided crossings. This coupling may be tuned by rotating the polarization of the linearly polarized trapping light. Using such spectroscopic measurements in combination with direct measurements of the trap frequencies, we completely characterise the trap in both the ground and first excited rotational states. This will enable quantitative studies of molecular collisions and lifetimes in the trap, as well as allowing us to design optical lattice potentials for future experiments.
Contributes to objectives:
16 – Contributes to understanding of microwave spectroscopy in the presence of the trap.

19 – Aids with the design of optical traps and lattices
22 – Allows us to understand how optical and magnetic fields affect molecules at the level of hyperfine states.

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

Synopsis: The most successful method for the creation of ultracold molecules from ultracold atoms involves magnetoassociation of the atoms using  an interspecies Feshbach resonance. To be able to predict positions of CsYb Feshbach resonances we require knowledge of the interaction between Cs and Yb atoms. By confining both Cs and Yb in an optical dipole trap we observe sympathetic cooling of Cs by Yb. The rate of this cooling is related to the interspecies thermalisation cross section, which we extract from fitting our results with our kinetic model. Measuring this cross section for mixtures Cs-170Yb and Cs-174Yb we optimise the CsYb interaction potential to reproduce the measurements. This improves our knowledge of the CsYb interaction potential and allows the prediction of scattering length for all isotopologs of CsYb. We also demonstrate the production of Bose-Einstein condensates of Cs and 174Yb an important step towards a quantum-degenerate mixture of the two species.
Contributes to objectives:
1- Allows predictions of Feshbach resonances for formation of CsYb molecules