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Experimental search for Gravitational Waves

Experimental search for Gravitational Waves. Geppo Cagnoli cagnoli@fi.infn.it INFN - Firenze University of Glasgow Physik-Institut der Universität Zürich/ETH 28 th June 2006. The GR prediction. Newton’s Theory “instantaneous action at a distance”. G mn = 8 pT mn. Einstein’s Theory

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Experimental search for Gravitational Waves

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  1. Experimental search for Gravitational Waves Geppo Cagnoli cagnoli@fi.infn.it INFN - Firenze University of Glasgow Physik-Institut der Universität Zürich/ETH 28th June 2006

  2. The GR prediction Newton’s Theory “instantaneous action at a distance” Gmn= 8pTmn Einstein’s Theory information carried by gravitational radiation at the speed of light Physik-Institut der Universität Zürich / ETH

  3. Sources of Gravitational Waves Mass quadruplemoment Small amplitude approximation • Compact object binaries • Pulsars • Neutron Star internal dynamics • Non symmetrical supernovae • Cosmological gravitational waves Physik-Institut der Universität Zürich / ETH

  4. New potential sources January 05: A swarm of 10,000 or more black holes may be orbiting the Milky Way's supermassive black hole, according to new results from NASA's Chandra X-ray Observatory. This would represent the highest concentration of black holes anywhere in the Galaxy. Physik-Institut der Universität Zürich / ETH

  5. Detection Principles -1 Inertia Dimensions • In the reference frame of the lab (Fermi’s coordinates) the effect of GW is pure mechanical. The potential is: • 3 types of detectors • Resonators • Interferometers • RF cavities Physik-Institut der Universität Zürich / ETH

  6. Detection Principles -2 DL L DL/L < 10 -21 Expected from astronomical sources Effect of a sinusoidal gravitational wave going through the slideon the space-time frame and on a circular distribution of free masses Figure: M.Lorenzini Physik-Institut der Universität Zürich / ETH

  7. Detection Principles -3 Two detectors fully developed: Resonant Masses Interferometers Figure: S. Reid Physik-Institut der Universität Zürich / ETH

  8. Theory of GW Detectors - 1 V Read-out h x f Detectorinternalnoise Readoutinternalnoise Detector Physik-Institut der Universität Zürich / ETH

  9. First attempt of buildinga resonant detector Sensitivitypattern Joseph Weber(~1960) Resonant barsuspended in the middle Piezoelectrictransducers Physik-Institut der Universität Zürich / ETH

  10. The Band Width of a resonant detector Read-out noise Detector noise DetectorBW x/h Physik-Institut der Universität Zürich / ETH

  11. Resonant detectors today Bars mechanicalsignalenhancement Spheres GW bursts excite the resonances of the test masses Capacitive + SQUIDor optical readout Physik-Institut der Universität Zürich / ETH

  12. A capacitive Read-out systemof a resonant detector Cryogenic Switch Transducer Decoupling Charging Line Capacitor C d M M i Bar L L L s i C T SQUID Matching Capacitive Amplifier Transformer Resonant Transducer Physik-Institut der Universität Zürich / ETH

  13. Physik-Institut der Universität Zürich / ETH

  14. Interferometric detectors:the concept • Monitoring the distances between free-flying masses with laser interferometer • The background noise comes from the readout and from the internal motion of the masses Physik-Institut der Universität Zürich / ETH

  15. A bit of history… • Gertsenshtein M E and Pustovoit V I 1962 Sov. Phys.—JETP 16 433 • Moss G E, Miller L R and Forward R L 1971 Appl. Opt. 10 2495b • Weiss R 1972 Q. Prog. Rep. Res. Lab. Electron. 105 54 Physik-Institut der Universität Zürich / ETH

  16. The Band Width of an interferometric detector x = h · L / 2 for each end mirror Read-out noise Detector noise DetectorBW Physik-Institut der Universität Zürich / ETH

  17. Interferometers today - 1 Fabry – Perot cavities • End mirrors positioned in theDark Fringe condition: laser beam is frequency modulated, the sidebands are detected • Multiple bouncingphase accumulation:laser power increasesfrom 20W to 1kW • Power recycling: number ofphotons in the interferometerincreases • Signal recycling:just the side bands are reflectedback in the interferometerGEO600 is the onlydetector that uses thistechnique to enhance the detector response in a narrow band Pendulumsuspensions Beamsplitter Photodiode Laser Physik-Institut der Universität Zürich / ETH

  18. Interferometers today - 2 Fabry – Perot cavities Pendulumsuspensions Beamsplitter Photodiode Laser Physik-Institut der Universität Zürich / ETH

  19. Interferometers today - 3 Fabry – Perot cavities Pendulumsuspensions Beamsplitter Photodiode The optics and suspensions are in vacuum to minimize fluctuation of index of refraction Laser Physik-Institut der Universität Zürich / ETH

  20. Interferometers today - 4 3 km 600 m TAMA 4 & 2 km 300 m AIGO 4 km Physik-Institut der Universität Zürich / ETH

  21. Real data from LIGO Physik-Institut der Universität Zürich / ETH

  22. Real data from GEO600 10 -17 Displacement [m] 10 -18 10 -19 [Hz] 100 1000 Physik-Institut der Universität Zürich / ETH

  23. Real data from Virgo Physik-Institut der Universität Zürich / ETH

  24. Detectors of 1st Generation 1ST GENERATION IS CLOSE TO REACH THEDETECTION RANGE FOR NS-NS COALESCENCE AT THE DISTANCE OF THEVIRGO CLUSTER (17MPc) LIGO VIRGO 10 -19 • 1ST GENERATION • FOR INTERFEROMETERS • STEEL SUSPENSIONS (APART GEO600) • ROOM TEMPERATURE • FOR RESONATORS • Al or AlCu • 100mK < T < 4K 10 -20 AURIGA NAUTILUS MiniGRAIL GEO600 10 -21 NS-NS 14 Mpc BH-BH 67 Mpc 10 -22 10 -23 10 -24 10 -25 10 100 1k 10k 1 Frequency [Hz] h Pulsars [ Hz –1/2 ] Supernovae NSvibration BUT THEEVENT RATEIS TOO LOW !! 1 EVENT/3 YRS MOST OPTIMISTICCASE Physik-Institut der Universität Zürich / ETH

  25. Future Detectors of Gravitational Waves • DUAL • Nested hollow cylinder resonant detector • AURIGA collaboration • Construction planned starting on 2009 • Ad. LIGO, Ad. Virgo and GEO HF • 2nd generation interferometers • Virgo + GEO600 collaboration • Commissioning starts on 2009 • 3rd Generation Interferometer • Cryogenic and underground interferometer • Construction envisaged by 2014 Physik-Institut der Universität Zürich / ETH

  26. DUAL – the concept read-out the differential deformations of two nested resonators The outer resonator is driven above resonance The inner resonator is driven below resonance πPhase difference 5.0 kHz useful GW band Physik-Institut der Universität Zürich / ETH

  27. DUAL performance M. Bonaldi et al. Phys. Rev. D 68 102004 (2003) Mo Dual 16.4 ton height 3.0m 0.94m SiC Dual 62.2 ton height 3.0m 2.9m Antenna pattern: like 2 IFOs colocated and rotated by 45° Q/T=2x108 K-1 Physik-Institut der Universität Zürich / ETH

  28. Real data from Virgo READOUT THERMALNOISE EARTHRELATEDNOISE CONTROL RELATED NOISE Physik-Institut der Universität Zürich / ETH

  29. Readout noise – shot noise √Hz • A fundamental limit to phase measurement is due to the quantum nature of light • Phase measurements to a level of 10 -13 rad require about 1 MW of laser power in the optical cavities • But more power = more fluctuating radiation pressure P=1 MW  F=3 mN  dF=1.5 DN · Dj ≥ 1/2 fN Physik-Institut der Universität Zürich / ETH

  30. Readout noiseThe Standard Quantum Limit Quantum limit onphase measurement Radiation pressure noise Strain [ 1/√Hz ] SQL For a simple Michelson interferometer (GEO HF parameters) RomanSchnabelMPG-AEI Hannover 10-21 Quantum noise with increased laser power (x100) 10-23 1 100 Frequency [ Hz ] Physik-Institut der Universität Zürich / ETH

  31. Beyond the SQL: Squeezed Light • In one representation of the EM field the two orthogonal states are the Amplitude Quadrature X1 and the Phase Quadrature X2 RomanSchnabelMPG-AEI Hannover Physik-Institut der Universität Zürich / ETH

  32. Beyond the SQL: Squeezed Light • In one representation of the EM field the two orthogonal states are the Amplitude Quadrature X1 and the Phase Quadrature X2 RomanSchnabelMPG-AEI Hannover Physik-Institut der Universität Zürich / ETH

  33. Beyond the SQL: Squeezed Light Noise reduction by squeezed light - 6 dB in variance Strain [ 1/√Hz ] 10-21 RomanSchnabelMPG-AEI Hannover Quantum limit onphase measurement Radiation pressure noise SQL 10-22 1 100 Frequency [ Hz ] Physik-Institut der Universität Zürich / ETH

  34. Squeezed light demonstrations [Vahlbruch et al., Phys. Rev. Lett., submitted (2005)]. [Chelkowski et al., Phys. Rev. A 71, 013806 (2005)]. Physik-Institut der Universität Zürich / ETH

  35. Intermediate frequencies 10-19 THERMALNOISE Strain [ 1/√Hz ] 10-25 1 10 k Frequency [ Hz ] From the realm of Quantum to the realm of Statistical Physics Physik-Institut der Universität Zürich / ETH

  36. Thermal noise • Non isolated system shows uncorrelated fluctuations of volume and temperature • The equipartition principle states that each observable has a mean energy equal to kBT/2 • The observable • Optical readout: part of the mirror sensed by the laser • Capacitive readout: the average position of the capacitor plates Physik-Institut der Universität Zürich / ETH

  37. Thermal noise reduction strategy Noise Log [S xx (w) ] R.K.Patria Statistical Mechanics Pergamon Press Log f • Linear systems & thermal equilibrium • Each dynamic variable <E>= kT • Fluctuation-Dissipation theorem Lower T  Lower thermal noise Thermal noise for Damped HarmonicOscillator Lower dissipation  Lower thermal noise Physik-Institut der Universität Zürich / ETH

  38. The most severe limit for IFOs:thermal noise from the coatings 10-19 Strain [ 1/√Hz ] 10-25 1 10 k Frequency [ Hz ] • Alternate layers of transparent materials with different index of refraction • Impedance mismatch andinterference produce highcoefficient of reflectivity • Its structure is not compact as the substrateDeposition with DIBS • 10 mm of coating produces morethermal noise than 10 cm of substrate QUANTUM COATINGS EGO SUBSTRATES Physik-Institut der Universität Zürich / ETH

  39. Suspensions at room temperature • Best material:silica (SiO2) • Silicate bonding • Tested on GEO600 Physik-Institut der Universität Zürich / ETH

  40. Silicon for mirrors and suspensions at low T • Thermal expansion null at 124K and 18K  main source of thermal noise is ruled out • High thermal conductivity • Monocrystal ingots up to 45cm diameter • Possibility of monolithic suspensions • Diffractive as well as transmissive interferometry allowed 5000 k 2.5e-6 a Physik-Institut der Universität Zürich / ETH

  41. Earth related noise - 1 • Test masses have to behave like free flying objects, yet they have to be suspended against gravity • Seismic motion always present has to be filtered Physik-Institut der Universität Zürich / ETH

  42. Earth related noise - 2:Isolation short-circuit Newtonian noise SEISMIC NOISE The Newtonian noisewill be dominant below 10 Hz for cryogenic detectors Surface waves die exponentially with depth: GO UNDERGROUND! Figure: M.Lorenzini Physik-Institut der Universität Zürich / ETH

  43. Further considerations • Building the most perfect inertial reference system • A system subjected to the quantum problem of measurement • All the fundamental parameters of the detector have to be CONTROLLED without introducing a significant noise Physik-Institut der Universität Zürich / ETH

  44. Detector Generations LIGO VIRGO 10 -19 10 -20 AURIGA NAUTILUS MiniGRAIL GEO600 Ad VIRGO 10 -21 10 -22 Mo DUAL 10 -23 SiC DUAL 10 -24 3rd GENERATIONINTERFEROMETER 10 -25 10 100 1k 10k 1 Frequency [Hz] h [ Hz –1/2 ] Physik-Institut der Universität Zürich / ETH

  45. BH-BH coalescence range NS-NS coalescence range GRB050509B 1ST GENERATION 2ND GENERATION 3RD GENERATION INTERFEROMETER Physik-Institut der Universität Zürich / ETH

  46. Beyond Earth based detectors:LISA Audio band1 Hz – 10 kHz LISA Physik-Institut der Universität Zürich / ETH

  47. A collaborative ESA NASA mission • Cluster of 3 S/C in heliocentric orbit • Trailing the earth by 20° (50 Mio km) • Equilateral triangle with 5 Mio km arms • Inclined against ecliptic by 60° Physik-Institut der Universität Zürich / ETH

  48. The spacecraft • LISA needs a purely gravitational orbit • Test masses have to be shielded from solar wind • Capacitive sensing of the test masses • Feedback loop to propulsion • FEEP thrusters with micro-Newton thrust Physik-Institut der Universität Zürich / ETH

  49. The Payload Physik-Institut der Universität Zürich / ETH

  50. LISA technology demonstration Torsion pendulum Flight test LISA 10-12 10-13 10-14 10-15 Physik-Institut der Universität Zürich / ETH

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