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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 2010 @Università degli Studi di Trento, Trento, Italy

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7 May 2010 (Morning)

Thermal noise

7 May 2010 (Morning)

Seismic noise, Quantum noise

0.Abstract

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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

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1. Seismic noise

Vibration of ground shakes mirrors.

Seismic noise limits sensitivity below 10 Hz.

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1. Seismic noiseHow can we reduce seismic noise ?

(1) Small seismic motion site

(2) Good vibration isolation system

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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.

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1. Seismic noise(2) Good vibration isolation system

Transfer function : (Motion of mirror)/(Motion of support)

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1. Seismic noise(2) Good vibration isolation system

Unfortunately, single pendulum does not have enough isolation forgravitational wave detection.

We need multi stage isolation system.

M. Punturo, GWDAW Rome 2010

VIRGO: Super Attenuator

Mirror

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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 Instrument64 (1993) 1337.

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1. Seismic noise(1) Small seismic motion site

Where is silent sites ? Underground !

BFO (Black Forest Observatory): -162mBRG (Berggieshübel seism Observatory): -36mGRFO (Graefenberg borehole station): -116m

Kamioka (Kamioka mine): -1000m

Kamioka mine

M. Punturo,

GWDAW Rome 2010

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1. Seismic noise(1) Small seismic motion site

Where is Kamioka mine ?

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Location of LCGTLCGT is planed to be built underground at Kamioka, where the prototype CLIO detector is placed.

By K. Kuroda (2009 May Fujihara seminar)

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1. Seismic noise(1) Small seismic motion site

Near Kamioka mine(deep snow …)

Kamioka mine entrance

Kamioka mine road (about 2 km)

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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 XMASSGravitational wave detector CLIOGeophysics Strain meter (100 m), Superconducting gravimeter

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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 …

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1. Seismic noise

All measurement was at center of mine.Mirror must be far from center !

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1. Seismic noise

Measurement outside of mine and shaft

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1. Seismic noise

Measurement at Atotsu office

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1. Seismic noise

Outside of Mozumi office

Exit of Mozumi shaft

Mozumi office

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1. Seismic noise

Measurement apparatus

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1. Seismic noise

Truck

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1. Seismic noise

Electric locomotive

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1. Seismic noise

Fixed accelerometer in Mozumi shaft

10 cm

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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 similarto horizontal one.

Results of other locationsare similar.

(1) Small seismic motion site

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1. Seismic noise(1) Small seismic motion site

Inside of mine

> 50 mSilent sufficiently !

Main mirrors50 m from ground

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1. Seismic noiseSmall 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.

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2. Quantum noise

Quantum noise

Quantum amplitude and phase fluctuations of light

Limit from quantum mechanics

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2. Quantum noise

What generates quantum fluctuation of light ?

Interference between light and vacuum fluctuationPhase and amplitude fluctuation

Phase fluctuation : Shot noise

Gravitational wave shifts phase of light.

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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.

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2. Quantum noiseAmplitude fluctuation : Radiation pressure noise

http://spacefiles.blogspot.com

Photons come at random (amplitude fluctuation). Back action of photon is also at random.→ Radiation pressure noise

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2. Quantum noiseCan amplitude fluctuation generate radiation pressure noise ?

Vacuum

Common motion of mirrors ?

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2. Quantum noiseCan 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.

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2. Quantum noiseHow 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 P1/2. Shot noise is inversely proportional to P1/2.

Radiation pressure noise : Interference between light and vacuum is proportional to P1/2. This is the back action to mirror. Radiation pressure noise is proportional to P1/2.

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2. Quantum noise

shot noise

quantum radiation pressure noise

standard quantum limit

quantum noise with 100x increased laserpower

P~

1~

P

m~

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

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2. Quantum noiseThere 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

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2. Quantum noiseMoreover, 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.

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2. Quantum noiseSignal enhancement without high power

Signal recycling mirror

B. J. Meers, Physical Review D 38 (1988) 2317. J. Mizuno et al., Physics Letters A 175 (1993) 273.

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2. Quantum noiseOr 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.

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2. Quantum noise

C.M. Caves, Physical Review D 23 (1981) 1693.

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2. Quantum noise

Not usual but squeezed vacuum

C.M. Caves, Physical Review D 23 (1981) 1693.

4242

2. Quantum noiseBrief history of squeezing

First squeezing : R.E. Slusher et al., Physical Review Letters 55 (1985) 2409.

Injection to Michelson interferometer : K. McKenzie et al.,, Physical Review Letters 88 (2002) 231102.

Squeezing in audio band (280 Hz ~) : K. McKenzie et al.,, Physical Review Letters 93 (2004) 161105.

Strong (10dB) squeezing : H. Vahlbruch et al.,, Physical Review Letters 100 (2008) 033602.

Injection to suspended interferometer : K. Goda et al.,, Nature physics 4 (2008) 472.

434343

H. Vahlbruch et al., Classical and Quantum Gravity 27 (2010) 084027.

Recent result

2. Quantum noise

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2. Quantum noiseRecent progress

H. Vahlbruch et al., Classical and Quantum Gravity 27 (2010) 084027.

Installation in GEO600

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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.

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2. Quantum noise

GEO600 LIGO3 Adv. LIGO3

Sakata1 Goßler2 Corbitt3 Ours4

meff. 1 kg 2,5 kg 10 kg 23 mg 0,5g 1 g 50 ng

P [kW] 10 10 830 1,2 0,003 20 0,06

P/m [kW/kg] 10 4 83 52*103 6 20*103 1,2*109

P/m [kW/kg] 3 1,3 2,9 48000 110 4500 5*109

1 N. Mavalvala, Elba conference (2008)2 C.M. Mow-Lowry et al., Journal of Physics:Congerence Series 32 362-367 (2006)3 T. Corbitt, Elba conference (2008)4 J.D. Thompson et al., Nature 452 72-76 (2008)

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2. Quantum noiseThis is only one example (and ours) in progress ….

SiN membrane(~50 nm, ~ 100 ng)

K. Yamamoto et al., Physical Review A 81 (2010) 033849.

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2. Quantum noiseAfter observation of radiation pressure noise ….

Beyond SQL

How ?

Negative correlation between shot noise and radiation pressure noise

Squeezing can make negative correlation.

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2. Quantum noiseNarrow band

Wide band : some tricks are necessary.

H.J. Kimble et al., Physical Review D 65 (2001) 022002.

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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

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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

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Thank you for your attention !

Vi ringrazio molto per la vostra attenzione !