Towards high-mass quantum physics with levitated nanoparticles
Main list: Physics and Astronomy Colloquia
Optomechanical devices monitor the displacement of a small mechanical oscillator using the light of an optical cavity with exquisite sensitivity, allowing for instance the recent detection of gravitational waves by the LIGO experiment (2017 Nobel prize). The optomechanical interaction can also lead to cooling and has allowed cooling to (or near) the quantum ground state of a range of mechanical devices, with the assistance of cryogenic cooling. Over the past decade or so, cooling the centre of mass motion of nanoparticle (on the 100-500 nm scale, about the size of a virus) levitated by light in a cavity has been a challenge for several experimental groups . Levitation by light at high vacuum would provide a high degree of decoupling from environmental heating and decoherence. Nevertheless, the problems are formidable: the oscillator must be cooled from room temperature (about n~10^7 quanta above the ground state) down to typical occupancies n<1. The key bottleneck was trapping the particle stably at high vacuum; particle loss issues held up the field for years, but in 2015-2017 it became possible to trap and cool down to $n~100$ including at UCL . This year, a technical breakthrough  means that the milestone of cooling of a levitated nanoparticle to the quantum ground state (n<1) is in view (and has already been tentatively reported at summer conferences by groups in Austria and Switzerland). In the talk I will review progress in levitated optomechanics, in particular cavity optomechanics, and including our work at UCL. A key driver of the field is for applications in quantum sensing, thus cheaper, so -called “table-top” versions of LIGO. Which may be used for quantum accelerometers or for exploring fundamental physics. I will review the Standard Quantum Limit (SQL) of optomechanical sensing which represents a trade-off between incoming imprecision noise (quantum shot noise of light) and measurement back-action noise. An unusual and interesting feature of the new levitated set-ups is that they are intrinsically 3D, while in contrast, standard optomechanics cools only a single degree of freedom so I will also look at the SQL in 3D.
Physics Theatre C
September 27, 2019
From: 10h00 To: 11h00
University of St Andrews
The oldest university in Scotland, with international renown for both research and education of undergraduates and postgraduates.