Cavity optomechanics: towards sensing at the quantum limit

Lead Research Organisation: University College London
Department Name: Physics and Astronomy

Abstract

The grand challenge of attempting to cool a small mechanical device towards its quantum ground state is driving intense activity in many leading experimental groups worldwide. What seemed an unfeasible target only a decade ago, now appears tantalisingly close: by means of optomechanical techniques, micromechanical resonators such as small mirrors and cantilevers have been cooled by several orders of magnitude, down to occupation numbers of order n~30. The ultimate goal of approaching the ground state (n~1) now seems a realistic prospect, although serious obstacles remain; among these, thermal coupling to the environment is the most serious.However, within the last year, three groups (including the PI's) have independently proposed a novel scheme which has a fundamental new design: a dielectric nanosphere, optically levitated in a cavity and cooled by dipole forces arising from the optical field. The lack of mechanical connection to the cavity structure in a sense insulates the device from important sources of thermal noise and gives this scheme a unique edge in relation to conventional devices. The project brings together experimental and theory groups from London and Southampton with the ultimate goal of successfully implementing this scheme experimentally, for the first time. In addition, we aim to thoroughly understand the underlying physics theoretically by undertaking complete and realistic simulations of the optically cooled nanosphere system.Once the quantum limit is achieved, the main target is to operate the device in this regime. The rewards are potentially great. This is an attainable quantum technology which offers the prospect of unparalleled sensitivity in measurement, limited only by the Heisenberg uncertainty principle. For example, it is for this reason that these devices are used for gravitational-wave detectors, which require extraordinarily precise detections of displacement. They offer also the possibility of fundamental insights into the quantum-classical border: it may be possible to investigate superpositions which differ only by the displacement of a macroscopic object. Some experimental groups are investigating dipole-force coupling cavity optomechanics using a BEC (Bose Einstein Condensate) as the mechanical oscillator. In this case, the target is already in the ground state so it is already possible to explore the quantum regime. We will also investigate this regime theoretically, in order to establish whether quantum effects like squeezing (which improve sensing in the quantum regime) may be viably generated in such a scheme, as two of the co-applicants have already identified a potentially promising regime.Finally, taking the long view, we note that in parallel to this work, small sensors such as micron-sized cantilevers are actively being developed for biosensing applications (for ultra-sensitive detection of biomolecules or as force sensors). UCL, in particular the LCN (London Centre for Nanotechnology) is a leader in this field. On the otherhand, groups (such as the Caltech group of Vahala) working to cool optomechanical devices to the quantum limit are already testing their potential as biosensors.A desirable ambition, in the long-term would be to achieve a merger of these two directions: quantum limited detection and biosensing. We will explore the viability of employing schemes based on our dielectric nanospheres.

Planned Impact

An important long-term aim of this project is to develop a new type of quantum technology, offering unrivalled sensitivity of measurement. We envisage that the ability to detect tiny forces and displacement (at the single molecular level) will be of significant interest in chemical and bio-sensing. We have specifically chosen our team and project partners, who range from physicists to engineers, so that we can both study the fundamental aspects of this work while also recognising and exploiting important sensing applications when they arise. This programme will initiate UK participation in the development of this new technology where it currently has little or no presence. Our research will thus provide expertise in this area and we will be in a good position to provide expert advice to UK government and industry on potential applications and current worldwide trends in this technology. This research capability will add substantially to the UK's competitiveness in this emerging new quantum technology. As part of this programme, we aim to develop stronger links with the London Nanotechnology Centre (LCN) and medical faculties at UCL who are developing cantilever type bio-senors specifically for health care. The contact will allow us access to potential users of our technology outside the physical sciences, while they will also benefit from our expertise in quantum sensing. The technology and expertise in both experiment and theory will be useful in quantum metrology and therefore eventually also to standards laboratories. Advances here will be communicated to the UK's National Physical Laboratory. Any commercially useful intellectual property will be patented. This service, as well as assistance in technology transfer, is offered through the UCL Business office and at Southampton via Research and Innovation services. As well as publishing our results through the usual established channels such as journal publications, conferences and talks, we aim to bring together interested groups within the UK, and also key international groups, for a quantum sensing sandpit/workshop. This event will also involve a public lecture on quantum sensing and will be given by an esteemed visiting scientist in the field. Other beneficiaries of this work are the students and PDRAs who will be trained during the project. It will provide them with valuable experimental experience in the application of lasers, optics and electronics as well as vacuum technique, all of which are of importance and relevant to many experimental labs in physics and chemistry. We point out that these skills are also important to research and development in government labs, but also to many high tech industries and eventually to wealth creation in the UK. The significant theory component of this research will also provide important training in modern, advanced theoretical quantum physics. These acquired skills will be transferable to a wide range of subject areas which are reliant on skilled graduates in the physical sciences. The students and PDRA's will develop a range of programming and modelling skills, which will have wider application, particularly in the financial sector. The applicants have a particularly good record in this area with past students in jobs ranging from the health and eye care industry to finance, as well as in academia. This emerging field has great potential for public outreach activities, as the long term aim of demonstrating a mesocale particle cooled to the quantum limit inspires wide public interest. The issue of whether it is possible to observe quantum behavior in a small mechanical device is inspiring interest beyond the specialist science community. We aim therefore to disseminate our results and progress by our press releases, websites, a research blog devoted to this project, as well as lectures through the UCL Science Centre for the general public, teachers and school children.

Publications

10 25 50
 
Description Through this grant we have discovered a way of measuring temperature of a single nano particle. This is something that was impossible using conventional methods. We now know of people who are utilising this method in academia. We have also developed techniques to cool the centre-of-mass motion of particles using light. The particle is trapped within a RF Paul trap which is commonly used for nano particle analysis. We are the first to cool these particles in vacuum using a cavity field. This breakthrough will allow a range of new applications some of which we aim to further explore. These include the development of sensors which will give information on mass, charge and shape of nanoparticles. The low dissipation in vacuum looks promising for an exquisitely sensitive force sensors. Basic applications include a way to test quantum mechanics on macroscopic length and mass scales.
Exploitation Route They are already used by others but we expect that our work will be used in fundamental physics. Identified areas include sensitive force measurements which have application in gravitational wave detection and for studying correction to standard Newtonian gravity at short length scales. The system developed by us also appears promising for tests of quantum mechanics on macroscopic scales and we have now used these to put limits on dissipative models of wavefunction collapse.
Sectors Energy,Other

URL https://arxiv.org/abs/1907.06046
 
Description Although this grant is not finished our work has led to significant impact in nano particle characterisation when trapped in optical fields. This is currently being used in other groups around the world to determine temperature of nano particles that are trapped in optical tweezers. This work has led to more work in this area and has been at the forefront of levitated optomechanics.
First Year Of Impact 2014
Sector Education,Other
Impact Types Societal

 
Description Nonclassicalities and Quantum Control at the Nanoscale
Amount £1,166,350 (GBP)
Funding ID EP/J014664/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2012 
End 11/2015
 
Description Quantum feedback control of levitating opto-mechanics
Amount £579,937 (GBP)
Funding ID EP/K026267/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 11/2013 
End 11/2016
 
Description Collaboration with Coherent Scotland 
Organisation Coherent
Department Coherent Scotland
Country United Kingdom 
Sector Private 
PI Contribution This is in commercial confidence.
Collaborator Contribution Expertise in lasers.
Impact This is in commercial confidence.
Start Year 2017
 
Description Collaboration with Princeton University 
Organisation Princeton University
Country United States 
Sector Academic/University 
PI Contribution Experimental support of a number of programmes
Collaborator Contribution Theoretical support
Impact Publications across a range of grants.
 
Description Erlangen University Collaboration 
Organisation Friedrich-Alexander University Erlangen-Nuremberg
Department Department of Physics
Country Germany 
Sector Academic/University 
PI Contribution Experimental work
Collaborator Contribution Theoretical support
Impact 1 Publicatons
Start Year 2015
 
Description Griffith University Collaboration 
Organisation Griffith University
Country Australia 
Sector Academic/University 
PI Contribution Working out details on trapping diamond and other nanoparticles
Collaborator Contribution Transfer of expertise in ion trapping.
Impact None as yet.
Start Year 2016
 
Title An aligned electro-optical hybrid trap spectrometer for cooling and characterising nanoparticles 
Description Development of cavity mass spectrometer with enhanced sensitivity due to an optical cavity. 
IP Reference GB1522694.7 
Protection Patent application published
Year Protection Granted 2016
Licensed No
Impact None yet.