1 Kazuhiro Yamamoto Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut) Institut fuer Gravitationsphysik, Leibniz Universitaet Hannover Fundamental noise of interferometric gravitational wave detector (Seismic noise and Quantum noise) 7 May degli Studi di Trento, Trento, Italy

2 7 May 2010 (Morning) Thermal noise 7 May 2010 (Morning) Seismic noise, Quantum noise

0.Abstract 3 I would like to explain … (1) Seismic motion Investigation for silent site selection. (2) Quantum noise Reduction of shot noise Observation of radiation pressure noise Beyond Standard Quantum Limit

Contents 1. Seismic noise 2. Quantum noise 3. Summary 4

5 1. Seismic noise Vibration of ground shakes mirrors. Seismic noise limits sensitivity below 10 Hz.

6 1. Seismic noise How can we reduce seismic noise ? (1) Small seismic motion site (2) Good vibration isolation system

7 1. Seismic noise (2) Good vibration isolation system Mirrors are suspended. Slow motion Mirror follows motion of support point. Rapid motion Mirror can not follow motion of support point.

8 1. Seismic noise (2) Good vibration isolation system Transfer function : (Motion of mirror)/(Motion of support)

9 1. Seismic noise (2) Good vibration isolation system Unfortunately, single pendulum does not have enough isolation for gravitational wave detection. We need multi stage isolation system. M. Punturo, GWDAW Rome 2010 VIRGO: Super Attenuator Mirror

10 1. Seismic noise (1) Small seismic motion site Site selection is essential ! How do we measure seismic motion ? It is not easy even if seismic motion is typical one … (a) Excellent (not usual !) commercial accelerometer (b) Sensor made by ourselves … One example : Michelson interferometer A. Araya et al., Review of Scientific Instrument 64 (1993) 1337.

11 1. Seismic noise (1) Small seismic motion site Where is silent sites ?Underground ! BFO (Black Forest Observatory): -162m BRG (Berggieshübel seism Observatory): -36m GRFO (Graefenberg borehole station): -116m Kamioka (Kamioka mine): -1000m Kamioka mine M. Punturo, GWDAW Rome 2010

12 1. Seismic noise (1) Small seismic motion site Where is Kamioka mine ?

13 Location of LCGT LCGT is planed to be built underground at Kamioka, where the prototype CLIO detector is placed. By K. Kuroda (2009 May Fujihara seminar)

14 1. Seismic noise (1) Small seismic motion site Near Kamioka mine (deep snow …) Kamioka mine entrance Kamioka mine road (about 2 km)

15 1. Seismic noise (1) Small seismic motion site There are many scientific apparatus in Kamioka mine. Neutrino physics (Kamiokande : Nobel prize in 2002) Super Kamiokande, Kamland (neutrino oscillation) Dark matter search XMASS Gravitational wave detector CLIO Geophysics Strain meter (100 m), Superconducting gravimeter

16 1. Seismic noise (1) Small seismic motion site Many people measured seismic motion in Kamioka mine. 100 times smaller seismic motion at center of Kamioka mine. However …

17 1. Seismic noise All measurement was at center of mine. Mirror must be far from center !

18 1. Seismic noise Measurement outside of mine and shaft

19 1. Seismic noise Measurement at Atotsu office

20 1. Seismic noise Outside of Mozumi office Exit of Mozumi shaft Mozumi office

21 1. Seismic noise Measurement apparatus

22 1. Seismic noise Truck

23 1. Seismic noise Electric locomotive

24 1. Seismic noise Fixed accelerometer in Mozumi shaft 10 cm

25 1. Seismic noise Outside of mine <1 Hz (Outside of mine) =(Center of mine) >1 Hz (Outside of mine) >(Center of mine) Vertical motion is similar to horizontal one. Results of other locations are similar. (1) Small seismic motion site

26 1. Seismic noise (1) Small seismic motion site Inside of mine > 50 m Silent sufficiently ! Main mirrors 50 m from ground

27 1. Seismic noise Small summary of seismic motion Underground site is excellent. 100 times smaller seismic motion Depth of mirror must be more than 50 m. If not so, seismic motion is not so small even if the site is country side … We need excellent and huge vibration isolation system.

28 2. Quantum noise Quantum noise Quantum amplitude and phase fluctuations of light Limit from quantum mechanics

29 2. Quantum noise What generates quantum fluctuation of light ? Interference between light and vacuum fluctuation Phase and amplitude fluctuation Phase fluctuation : Shot noise Gravitational wave shifts phase of light.

30 How do we reduce shot noise ? 2. Quantum noise Dark fringe No light at photo detector (if gravitational wave does not come) If there is DC power, interference between this DC light and vacuum fluctuation disturbs phase measurement.

31 2. Quantum noise Amplitude fluctuation : Radiation pressure noise Photons come at random (amplitude fluctuation). Back action of photon is also at random. → Radiation pressure noise

32 2. Quantum noise Can amplitude fluctuation generate radiation pressure noise ? Vacuum Common motion of mirrors ?

33 2. Quantum noise Can amplitude fluctuation generate radiation pressure noise ? Vacuum Differential motion of mirrors due to vacuum from output port C.M. Caves, Physical Review Letters 45 (1980) 75.

34 2. Quantum noise How do shot and radiation pressure noise depend on laser power (P)? Shot noise : Gravitational wave signal is proportional to P. Interference between light and vacuum is proportional to P 1/2. Shot noise is inversely proportional to P 1/2. Radiation pressure noise : Interference between light and vacuum is proportional to P 1/2. This is the back action to mirror. Radiation pressure noise is proportional to P 1/2.

35 2. Quantum noise shot noise quantum radiation pressure noise standard quantum limit quantum noise with 100x increased laserpower How do shot and radiation pressure noise depend on laser power (P)? Standard Quantum Limit (SQL) Lower limit of summation of shot noise and radiation pressure noise

36 2. Quantum noise There is an optimal power. However, this value is higher than usual laser power. Development of high power laser (~100 W) is in progress. One example

37 2. Quantum noise Moreover, power recycling Power recycling mirror R.W.P. Drever et al., in Quantum Optics, Experimental Gravity, and Measurement Theory, (Plenum, New York, 1983), p. 503.

38 2. Quantum noise Signal enhancement without high power Signal recycling mirror B. J. Meers, Physical Review D 38 (1988) J. Mizuno et al., Physics Letters A 175 (1993) 273.

39 2. Quantum noise Or squeezing ! Quantum amplitude and phase fluctuations of light Heisenberg uncertainty principle The product of amplitude and phase fluctuation has lower limit. However, phase (or amplitude) fluctuation itself has no lower limit ! Squeezing : smaller phase fluctuation (but larger amplitude fluctuation) C.M. Caves, Physical Review D 23 (1981) 1693.

40 2. Quantum noise C.M. Caves, Physical Review D 23 (1981) 1693.

41 2. Quantum noise Not usual but squeezed vacuum C.M. Caves, Physical Review D 23 (1981) 1693.

42 2. Quantum noise Brief history of squeezing First squeezing : R.E. Slusher et al., Physical Review Letters 55 (1985) Injection to Michelson interferometer : K. McKenzie et al.,, Physical Review Letters 88 (2002) Squeezing in audio band (280 Hz ~) : K. McKenzie et al.,, Physical Review Letters 93 (2004) Strong (10dB) squeezing : H. Vahlbruch et al.,, Physical Review Letters 100 (2008) Injection to suspended interferometer : K. Goda et al.,, Nature physics 4 (2008) 472.

43 H. Vahlbruch et al., Classical and Quantum Gravity 27 (2010) Recent result 2. Quantum noise

44 2. Quantum noise Recent progress H. Vahlbruch et al., Classical and Quantum Gravity 27 (2010) Installation in GEO600

45 2. Quantum noise There is an optimal sensitivity. (Shot noise) ~ (Radiation pressure noise) Current status (Shot noise) >> (Radiation pressure noise) Nobody has observed radiation pressure noise. Observation itself is an interesting topic.

46 2. Quantum noise GEO600LIGO 3 Adv. LIGO 3 Sakata 1 Goßler 2 Corbitt 3 Ours 4 m eff. 1 kg2,5 kg10 kg23 mg0,5g1 g50 ng P [kW] ,20,003200,06 P/m [kW/kg] * *10 3 1,2*10 9  P/m [  kW/kg] 31,32, * N. Mavalvala, Elba conference (2008) 2 C.M. Mow-Lowry et al., Journal of Physics:Congerence Series (2006) 3 T. Corbitt, Elba conference (2008) 4 J.D. Thompson et al., Nature (2008)

47 2. Quantum noise This is only one example (and ours) in progress …. SiN membrane (~50 nm, ~ 100 ng) K. Yamamoto et al., Physical Review A 81 (2010)

48 2. Quantum noise After observation of radiation pressure noise …. Beyond SQL How ? Negative correlation between shot noise and radiation pressure noise Squeezing can make negative correlation.

49 2. Quantum noise Narrow band Wide band : some tricks are necessary. H.J. Kimble et al., Physical Review D 65 (2001)

50 3.Summary Quantum noise Current status (Shot noise) >> (Radiation pressure noise) Reduction of shot noise : High power laser, Recycling, Squeezed vacuum Observation of radiation pressure noise Beyond Standard Quantum Limit

51 Seismic motion Underground site is excellent. 100 times smaller seismic motion Depth of mirror must be more than 50 m. If not so, seismic motion is not so small even if the site is country side … We need excellent and huge vibration isolation system. 3.Summary

52 Thank you for your attention ! Vi ringrazio molto per la vostra attenzione !