This project is to create ultralow loss cavity optomechanics through optical dilution for use in white light cavity to reduce quantum noise in gravitational wave detectors.

Optical springs:  towards measurements below the standard quantum limit 

We will be fabricating low noise resonators with international partners in Austria, Taiwan, Holland and France.  These resonators are designed to have a macroscopic mass suspended with nanoscale suspension, in order to achieve extremely low mechanical coupling. We can then use radiation pressure to achieve thermal noise free optomechanics.


Optical springs are created by radiation pressure forces in optical cavities. This radiation pressure allows the stiffness and resonant frequencyFigure 1. An optical cavity with a %u201Ccat-flap%u201D resonator mirror design (the purple part is the coated mirror) of a mechanical resonator to be raised without adding extra mechanical coupling. Current techniques have managed to achieve a quality factor enhancement of approximately 50-fold. We aim to optimise the optical stiffening process by using a resonator with an extremely small mechanical stiffness provided by nanoscale suspension, thus allowing the majority of the restoring force to be provided by radiation pressure. We aim to eventually achieve a Q-factor enhancement of over 1000, with an ultimate Qf product of more than 1013. This is an extremely challenging task, which requires expertise in optical experimentation techniques, cavity locking and technical noise mitigation.

An opto-mechanical system as shown in Figure 1 has been designed.  The cat-flap resonator, shown in Figure 2, is trapped in a high power laser beam which provides the radiation pressure restoring force. This resonator is a highly customised component which requires extensive modelling, design and specialised fabrication. The project involves modelling this resonator to minimise unwanted mechanical modes in the bulk, suspension and dielectric mirror coatings, as well as losses through clamping, recoil and other means. The first iteration of the experiment aims to achieve an extremely high quality factor with the cat-flap resonator, while the second iteration aims to integrate this design into an optomechanical filter in an interferometer.

A working gravitational wave detector filter cavity has the potential of measuring macroscopic objects with resolution better than the “standard quantum limit” predicted by naïve application of quantum mechanics. This offers a new technique for improving gravitational wave sensitivity for signals in the frequency range of 100 Hz to 10 kHz. Successful trapping of the cat-flap resonator also opens new areas in macroscopic quantum mechanics by obtaining extremely high quality factors at relatively low frequencies, compared to other quantum optomechanics experiments.

Figure 2.(a) Cat-flap resonator with membrane suspension. (b) Resonator with nanowire suspension (c) Micrograph of nanowire suspended resonators


Applicants should have excellent academic records and preferably an internationally peer reviewed paper. General UWA PhD entrance requirements can be found on the Future Students website.

Suggested reading

Blair, D., Ju, L., Zhao, C., Wen, L., Chu, Q., Ma, Y., Page, M., Blair, C., Fang, Q., Miao, H., 'The development of ground based gravitational wave astronomy and opportunities for Australia-China collaboration', International Journal of Modern Physics A, 30, 28-29, pp. 1545019. (2015)
Blair, D., Ju, L., Zhao, C.N., Wen, L.Q., Miao, H.X., Cai, R.G., Gao, J.R., Lin, X.C., Liu, D., Wu, L.A., Zhu, Z.H., Hammond, G., Paik, H.J., Fafone, V., Rocchi, A., Blair, C., Ma, Y.Q., Qin, J.Y., Page, M, 'The next detectors for gravitational wave astronomy', Science China: Physics, Mechanics and Astronomy, 58, 12, pp. 1-34.  (2015)
Page, M., Ma, Y., Blair, D., Zhao, C., Ju, L., Pan, H.-W., Chao, S., Mitrofanov, V., Sadeghian, H., ‘Towards thermal noise free optomechanics’, (refereed version currently in submission process to Journal of Physics D: Applied Physics)
Miao, H., Ma, Y., Zhao, C., Chen, Y., ‘Enhancing the bandwidth of gravitational wave detectors with unstable optomechanical filters’, Physical Review Letters, 115, 211104 (2015)
Blair, D.G., Howell, E.J., Ju, L., Zhao, C., Advanced Gravitational Wave Detectors, Cambridge University Press, USA (2012)
Corbitt, T., Chen, Y., Innerhofer, E., Müller-Ebhardt, H., Ottaway, D., Rehbein, H., Sigg, D., Whitcomb, S., Wipf, C., Mavalvala, N., ‘An All-Optical Trap for a Gram-Scale Mirror’, Physical Review Letters, 98, 150802 (2007)