The research group currently consists of Shaun Laing (PhD student), Rafal Gajewski (PhD student), and Madeline Harris (MPhys project student).
EPSRC INSQT: International Network in Space Quantum Technologies
EPSRC LeviNet: International Quantum Technologies Network for Levitated Optomechanics
The MAQRO Mission seeks to "harness space for achieving long free-fall times, extreme vacuum, nano-gravity, and cryogenic temperatures to test the foundations of physics in macroscopic quantum experiments". This effort is led by Rainer Kaltenbaek of University of Ljubljana, Solvenia. The effort started in 2010 and I have been involved since ~2014
Highlights of my involvement include
- Adoption of Talbot geometry (2015); further details below.
- Representing MAQRO at Lisbon workshop on Quantum Technologies (September 2017).
- Academic advisory role during ESA CDF Study (2018) 1.
Publication themes, context, and impact
Matterwave interferometric velocimetry of cold atoms
My PhD, in the Freegarde group (Southampton), started with a nearly empty lab and the goal of using matterwave interferometry of cold atoms to produce a cooling effect, quite different from standard Doppler cooling, which could be applied to species not suitable for Doppler cooling, such as molecules3.
Together with a number of other PhD students, we produced a working experiment performing Raman oscillations on cold rubidium atoms, and several theoretical publications. The publication on velocimetry2 captures much of what we originally set out to do, and rounds off my involvement with this experiment.
Parabolic Mirror for levitated optomechanics
Before joining the Ulbricht group to build their first levitated optomechanics setup, I was employed by the Optoelectronics Research Centre to work on fibre lasers. There, I learned the techniques and capabilities of this technology. On joining the Ulbricht group, I advocated that we build our system using telecommunications wavelength 1550nm fibre lasers, to exploit the power and stability of this mature technology. However, when building the first traps, we found a lack of good quality aspheric lenses designed for this wavelength. I suggested reflective optics and, after some discussions, we ordered a custom diamond-turned parabolic aluminium mirror.
This design has a number of advantages: not only is it achromatic, but also light back-scattered from the particle is collimated while the unscattered laser light diverges strongly. Therefore, about one metre from the trap, collimated back-scattered light and the unscattered trapping laser light are of equal intensity and a detector placed here sees a strong modulation from interference, in stark constrast to ~1 part per thousand in forward-scattering 4. Furthermore, back-scattered light is more sensitive to position than forward scatter. We knew this based on simple arguments, and it has since been shown rigorously that this is the optimally sensitive arrangement 5.
A practical problem with back-scatter is that there is a large path difference, and consequent drift in the phase, compared with the much more stable forward-scatter arrangement. However, in the reflective arrangement, this path difference is only some millimetres, and the drift is much less of a problem.
We used this geometry in work at Swansea6, and 1550nm light has since been adopted by other levitated optomechanics groups. Not only are the lasers extremely stable, but also the absorption in glass nanoparticles appears to be less than at 1064nm, leading to more stable trapping at intermediate gas pressures.
Near-field matterwave interferometry
While employed by the Ulbricht group (Southampton), I collaborated with Klaus Hornberger and Stefan Nimmrichter to design a Talbot-effect interferometer for matterwaves 7. The original plan was to adapt existing work on the Talbot-Lau interferometer, which uses three gratings at least one of which is absorbitive, to measure matterwave properties of macromolecules 8.
However, for the case of nanoparticles, we realised that we could start with a near point-like source which, together with spatially-resolving position detection, would allow us to use a single grating. This simplified the theoretical description and experimental implementation, and reduced the sources of decoherence.
Soon after publication, this approach was adopted by the MAQRO Consortium 9.