In the September 2017 issue of Nature Photonics, Dr A. Rahman and Professor P. Barker from Physics and Astronomy at UCL report on the first demonstration of optical refrigeration of a submicrometre particle suspended by laser light. The tiny levitated cryostat, consists of a single nanocrystal of Yb3+:YLF crystal cooled to temperatures as cold as −143 °C by illuminating, trapping and aligning it with a single laser beam. Their work has shown that the internal temperature of the nanocrystal can be controlled over a wide range using different trapping laser wavelengths. The laser polarization controls the orientation of the trapped crystal and maximizes its cooling. This development is a further important step towards bringing these macroscopic systems into the quantum regime.


Citation: Laser refrigeration, alignment and rotation of levitated Yb3+:YLF nanocrystals, A.T.M. Anishur Rahman and P. F. Barker, Nature Phonics, Nature Photonics 11, 634–638 (2017)

In a 3 minute video with the online journal, Erika Aranas and other group members explain the work


Our paper “Nonlinear dynamics and strong cavity-cooling of levitated nanoparticles” has been recently published in Physical Review Letter! It has been also selected to be a PRL Editor’s suggestion!

You can find the paper here.


14054221_10100615704706855_8825210623784134533_nCongratulations to Lia (Ying Lia Li) for passing her Ph.D. viva on the 22nd September! Her Ph.D. thesis is titled ‘Cooling and sensing using whispering gallery mode resonators’.

Dr. Li has taken on a post-doc position with Prof. Barker to further her research on whispering gallery modes.


Members of the group attended Quantum Engineering of Levitated systems meeting (Benasque)benasque

 (left) Giacomo Fonseca, Peter Barker, Nathanel, Antonio, Tania Monteiro. (right) Giacomo, Nathanael, Antonio.

spherecoolingOur paper on using optical whispering gallery modes (WGM) to detect and cool mechanical modes of a microsphere-cantilever and the motion of the tapered fibre used to couple light into the WGM has been published in Optics Express!
Ying Lia Li, James Millen, and P. F. Barker, “Simultaneous cooling of coupled mechanical oscillators using whispering gallery mode resonances,” Opt. Express 24, 1392-1401 (2016) 

We have just uploaded a new experimental paper on the ArXiv, click here to view it.
he paper is titled ‘Macroscopic Center-of-Mass Cooling using Whispering Gallery Mode Resonances’ and covers the main achievements from Lia’s Ph.D. project.

As technology continues to miniaturize, we need new ways to control micro-devices. Light is an excellent tool for both measuring the motion of small objects as well as manipulating them. We show that by trapping light from an ultra-thin optical fiber within a glass sphere (diameter of human hair), we can detect the displacement between them that is smaller than the size of an atom! Using this transduction we reduce the natural thermal vibrations from the environment by cooling the motion of both objects by almost 300 C. This is the first time this has been achieved on two objects at once, or with objects this large and heavy.