1. Optomechanical Devices for Improving the Sensitivity of Gravitational Wave Detectors Chunnong Zhao for Australian International Gravitational wave Research centre University of Western Australi a

2. The University of Western Australia Outline Gravitational wave detectors and quantum noise limits Squeezed vacuum injection, and white-light cavity for improving the sensitivity Optomechanical filters for achieving frequency- dependent squeezing and white-light cavity Thermal noise issue, noise-free optical dilution and mechanical resonator design Summary  2 2

3. The University of Western Australia  3 3 Fabry-Perot Cavity Beam Splitter Power Recycling Cavity Signal Recycling Mirror Nd:YAG laser = 1064nm Gravitational wave detector

4. Quantum noise limited sensitivity Conventional detector Frequency-dependent squeezed vacuum injection Phase-squeezed vacuum injection White-light cavity 4

5. The University of Western Australia Demonstration of squeezed vacuum injection on LIGO detector H1 Nature Photonics, 7, p 613-619, (2013)  5 5

6. The University of Western Australia Frequency-dependent squeezing injection  6 6 The filter cavity requirements: Low optical loss Low linewidth ~100Hz Tuneable for optimization

7. The University of Western Australia Frequency-dependent squeezed vacuum A lossless cavity is an ideal unity gain filter, and a ideal frequency- dependent squeezing angle rotator. The corner frequency of the rotator is the corner frequency of the cavity. For Advanced LIGO type detector, the corner frequency should be ~100Hz. To optimize a detuned interferometer detector, more than 2 filter cavities with optimized detuning and linewidth are required. These requirements lead to the alternative choice of active optomechanical filters.  7 7

8. The University of Western Australia Frequency-dependent squeezing injection  8 8 Optomechanical filter cavity can have very narrow linewidth and be tuneable by tuning the pump light

9. The University of Western Australia Narrow-band optomechanical filters  9 9

10. The University of Western Australia Narrow-band optomechanical filters J. Qin, et al., PRA 89, 041802(R) (2014)  10

11. The University of Western Australia Narrow-band optomechanical filters  11

12. The University of Western Australia Narrow-band optomechanical filters Classical noise ellipse angle rotation  12

13. The University of Western Australia White-light cavity  13  Negative dispersion medium

14. The University of Western Australia White-light cavity  14 ITM and SEM form a cavitythat is transparent to the GW signal Optomechanical cavity provide negative dispersion

15. The University of Western Australia Negative dispersion and white-light cavity  15

16. The University of Western Australia Negative dispesion and white-light cavity Negative dispersion cavity response: Normal cavity round-trip phase lag: Phase cancelation requirement:  16

17. The University of Western Australia Negative dispersion  17

18. The University of Western Australia Negative dispersion  18

19. The University of Western Australia Negative dispersion  19

20. The University of Western Australia Negative dispersion  20

21. The University of Western Australia Thermal noise The thermal noise of the mechanical resonator will be detrimental to all the benefits mentioned above.  21

22. The University of Western Australia Optical dilution Mechanical frequency shift from 12Hz -> 1kHz The problem: quantum radiation pressure noise and instability (negative damping) T. Corbitt, et al, PRL 99, 160801 (2007)  22

23. Optical dilution Quantum destructive interference cancels the noise and damping 23

24. Optical dilution Frequency Shift from 6.2 kHz to 145 kHz Q-factor increased 50-fold. 24

25. Cat-flap resonators Cat-flap resonator Optical dilution of a cat-flap resonator The intrinsic (gravity-free) frequency of the silicon nitride cat-flap is ~20Hz while for the graphene we expect 0.2 Hz. Since both should be able to be diluted to 200kHz we have typical dilution factors of ~10 8 (SiN) and ~10 12 for graphene. 25

26. Cat-flap resonator 26

27. Optical dilution Partial reflective mirror Cat-flap mirror 27

28. The University of Western Australia Summary Optomechanical filters can potentially be used to improve the GW detector quantum noise limited sensitivity Thermal noise is the critical issue to the application The noise-free optical dilution with careful designed mechanical resonator is one of the solutions.  28