Our UCL theory team comprised of Marco and Alessio, collaborating with Jinglei Zhang at Scuola Normale Superiore and James (now with Markus Arndt) have published a paper titled ‘Quantum cooling and squeezing of a levitated nanosphere via time-continuous measurements’, which is in the New Journal of Physics.

This work is particularly interesting for the many nanosphere cavity cooling experiments being conducted around the world, including our very own! In the paper they find that the addition of continuous measurement of the system can help create more non-classical states, squeeze the nanosphere’s position, and enhance cooling, helping us to reach a mechanical ground state.

Direct link to the pdf: here


We recently released a new paper titled ‘Testing Wavefunction Collapse Models using Parametric Heating of a Trapped Nanosphere’ written by Dan Goldwater (one of our Ph.D students) in collaboration with Mauro Paternostro at Queen’s University.

In this paper we propose a protocol which we could use to test novel theories which alter quantum mechanics, so-called collapse theories. The strengths of our proposal are that it could be implemented using our already existing hybrid trap (see previous posts), although we would require a lower pressure and temperature than we have achieved so far; and that it appears capable of testing the leading collapse theory (CSL) over a large parameter range, giving it an edge over other experiments designed to the same end. This work has been interesting – we’re seeking to address foundational questions in the lab using new experimental techniques, leading us to study both the philosophical aspects of quantum mechanics and the technical details of proposed experimental set-ups.

It is currently on the arXiv: http://arxiv.org/pdf/1506.08782v1.pdf


11334000_924866107534569_548118734246015486_oOur Ph.D. student Lia (Ying Lia Li) went to ONNA2015 last week, which is a conference held by OIST University on tapered optical fibres. OIST University is based on the sub-tropical island of Okinawa, Japan and is thriving with great scientific research, as well as surrounded by beaches and jungle. Lia presented her new results on active feedback cooling of a microsphere-cantilever using a piezo element, as well as feedback cooling the mechanical modes of the coupling taper using the cavity enhanced optical dipole force. Tapered optical fibres are crucial for her work, as they allow her to excite whispering gallery modes within the microsphere and these resonances both enhance optical forces as well as transduce the centre-of-mass motion of both the microsphere-cantilever and the tapered optical fibre.

The ONNA2015 programme was crammed with invited speakers from around the world, on a broad range of subjects from nano-fabrication, non-linear optics, plasmonics and cold atoms.

The PRL paper on ‘Cavity Cooling a Single Charged Levitated Nanosphere’ has been highlighted in Nature Photonics! Click here to view the highlight. It provides an excellent overview of the experiment and the results, and is accessible for students and the general public.

Our leaving present for Dr. James Millen

In April we said goodbye to our postdoc Dr. James Millen who has now joined Prof. Markus Arndt’s group in the Quantum Nanophysics Group. He was awarded a Marie Curie Fellowship and will continue to work with levitated nanospheres (as well as other fascinating macroscopic objects!).

James worked in our group for a few years looking at cooling levitated silica nanospheres, which cumulated in the design and implentation of the cavity cooling experiment using a hybrid optical and ion trap. He has also overseen the development of the whispering gallery mode project and has been immensely useful for many other experiments within the whole group. Within his time here, he also collaborated on theorectical work looking at non-linear Brownian dynamics and thermodynamics with Dr. Janet Anders, as well as looking at the theory of cooling and squeezing nanoparticles with Dr. Alessio Serafini.

Everyone at UCL’s Optomechanics group wishes him the best of luck with his fellowship, and we gifted him with an engraving on his first ever ion trap! His website is here and is regularly updated with both research news as well as his public speaking events and lectures.

Our paper on cavity cooling nanospheres has been published in Physical Review Letters! You can find it here.

There is an accompanying popular physics article, published in Physics.


Here is some new work we have done predicting the effects of continuous measurement on cavity-cooled nanospheres: Quantum cooling and squeezing of a levitating nanosphere via time-continuous measurements. We predict that by measuring the cavity output and/or the light scattered from a cavity-cooled nanosphere, and using these measurements to feedback onto the dynamics of the particle, cooling, squeezing and the purity of the quantum state can be improved.


Continuously measuring the position and cavity-output can inmprove cooling

Continuously measuring the position and cavity-output can inmprove cooling