Gravitational-Wave Detectors

Transcription

1 Gravitational-Wave Detectors Roman Schnabel Institut für Laserphysik Zentrum für Optische Quantentechnologien Universität Hamburg Outline Gravitational waves (GWs) Resonant bar detectors Laser Interferometers - Quasi-free test mass mirrors - Photo-electric detection The GW detector GEO600 with squeezed light 2

2 GW Gravitational-wave Event from Colliding Black Holes Roman Schnabel Institut für Laserphysik Zentrum für Optische Quantentechnologien Universität Hamburg LIGO Data of Sept. 14 th,

3 LIGO Data of Sept. 14 th, 2015 Results (numerical solution of Einstein s equations) Distance from Earth: 1.3 billion light years. 5 Gravitational waves Binary system f BS To Earth L +Δ L λ Gravitational wave 6

4 Gravitational Wave Detectors Weber bars, f res ~ 1kHz Auriga, Italy 3 m long aluminum cylinder 2.3 tons 7 4 km LIGO Gravitational-Wave Detector 8

5 Gravitational-Wave Detection Laser interferometers Mirror 1 1) Quasi-free test mass mirrors 2) Laser light α Laser ~ km Mirror 2 Photo diode GW induced distance change 9 The Gravitational-Wave Detector GEO 600 GEO-HF: - 30kW - DC readout - OMC - Tuned, broadband SR - Squeezed Light 10

6 Free Mirrors 11 Suspended Mirrors in LIGO (40 kg each) 12

7 Gravitational-Wave Detection Mirror 1 1) Quasi-free test mass mirrors 2) Laser light α Laser ~ km Mirror 2 3) Interference Photo diode GW induced distance change 4) Photo-electric effect Photo-electric current modulated at GW frequency ( unbiased estimator ) 13 Statistic of Truly Random Photons Looks like a signal Photons per time interval N Time intervals 14

8 Statistic of Truly Random Photons but isn t, just photon shot noise! Photons per time interval N Time intervals 15 Shot Noise Probability [rel. units] Coherent state α = 100 N ˆ = N = α 2 =10000 Shot-noise Signal ~ N N ~ 1 N ~ 1 P Laser N N N N + N Photon number N 16

9 Increasing the Light Power Power-recycling mirror Mirror 1 Light absorption/ heating High power laser Mirror 2 Photo diode Photo-electric current 17 Is there a possibility to increase the signal/quantum noise ratio without increasing the laser power? Yes! On the basis of squeezed light! [Caves, Phys. Rev. D 23, 1693 (1981)] 18

10 Introduction of squeezed states of electro-magnetic fields: H. P. Yuen, Two-photon coherent states of the radiation field, Phys. Rev. A 13, (1976) 19 The Gravitational Wave Detector GEO 600 GEO-HF: - 30kW - DC readout - OMC - Tuned, broadband SR - Squeezed Light 20

11 Statistic of truly random Photons Photons per time interval N (Poissonian) Shot noise Time intervals 21 Statistic of quantum-correlated Photons Paradoxical! Photons per time interval N Squeezed shot noise (Sub-poissonian) A nonclassical effect! The semi-classical model fails: First, light propagates and interferes as a wave and, second, particles appear randomly During energy transfer Time intervals 22

12 Squeezed Counting Statistics Paradoxical! Probability [rel. units] Poisson statistics Squeezing factor: 10 db Noise squeezing Squeezing factor: 3 db Photon number N : First Generation of Squeezed Light First generation of squeezed states of light (-7%, -0.3 db): R. E. Slusher, L. W. Hollberg, B. Yurke, J. C. Mertz, J. F. Valley, Observation of squeezed states generated by four-wave mixing in an optical cavity. Phys. Rev. Lett. 55, 2409 (1985) First generation of squeezed states of light with PDC (-50%, -3 db): L.- A. Wu, H. J. Kimble, J. L. Hall, H. Wu, Generation of squeezed states by parametric down conversion. Phys. Rev. Lett. 57, 2520 (1986) In terms of S/N: 3 db squeezing = doubling the light power 24

13 Squeezing Laboratories First squeezed light: [Slusher et al., PRL 55, 2409 (1985)] Research labs with squeezed light (not complete): - Kimble (CalTech): teleportation: [Furuzawa et al., SCIENCE 282, 706 (1998)] - Grangier (Orsay); kitten: [Ourjoumtsev et al., SCIENCE, 312, 83 (2006)] - Schiller and Mlynek (Konstanz): tomography: [Nature 387, 471 (1997)] - Bachor and Lam (Canberra): 6dB at 1064nm [J. Opt. B 1, 469 (1999)] - Leuchs (Erlangen); ~7 db pulsed [Opt. Lett. 33, 116 (2008)] - Polzik (Copenhagen), [Neergaard-Nielsen et al., PRL 97, (2006)] - Furusawa (Tokyo); 9 db: [Takeno et al., Opt. Express 15, 4321 (2007)] - Fabre (Paris); Zhang, Peng (Shanxi); Andersen (Copenhagen); Mavalvala (MIT) - Nussenzveig (Sao Paulo); Pfister (Virginia); Squeezing Issues for GW Detection Squeezing at frequencies in the GW detection band (10 Hz to 10 khz) - Control beam as noise source identified [Bowen, RS et al., J. Opt. B 4, 421 (2002)], 421 (2002)], [RS et [RS al., Opt. et al., Comm. Opt. Comm. 240, , (2004)] 185 (2004)] - First Audioband squeezing [McKenzie et al., PRL 93, (2004)] - New control scheme [Vahlbruch, RS et al., PRL 97, (2006)] - 6 db over complete band [Vahlbruch, RS et al., NJP 9, 371 (2007] Compatibility with GW detector techniques - Power-recycling [McKenzie et al., PRL 88, (2002).] - Signal-recycling [Vahlbruch, RS et al., PRL 95, (2005)] - Suspended interferometer [Goda et al., Nat. Phys. 4, 472 (2008).] Strong continuous wave squeezing (>10 db) at 1064nm - [Vahlbruch, RS et et al., PRL 100, (2008)] - [M. Mehmet, RS et et al., PRA 81, (2010)] 26

14 Design of the GEO600 Squeezer [Henning Vahlbruch, PhD thesis, Hannover, 2008] - Gravitational Wave International Committee (GWIC) Thesis Prize S-AMOP DPG Thesis Prize The GEO600 Squeezed Light Laser Alexander Khalaidovski and Henning Vahlbruch, 2009/2010 Real-time control system: Nico Lastzka and Christian Gräf 28

15 Generation of Squeezed Light Pump field input (cw, 532nm) χ 2 -nonlinear crystal: MgO:LiNbO 3 or PPKTP Squeezed field output (cw, 1064nm) by parametric down-conversion (PDC) Standing wave cavity 29 Generation of Squeezed Light Nonlinear dielectric polarisation of matter by light (Taylor-expansion) P i = ε 0 ( χ ij E j + χ (2) E E + χ (3) E E E + h (2) B E + h (3) ijk B j k ijkl j k l ijk k j ijkl k B l E j +... ) i, j, k, l,... = x, y, z SHG, THG, Kerr effect, Faraday effect Cotton-Mouton effect Parametric Four wave mixing down-conversion, PDC (OPO,OPA) 2 nd order terms in detail: P (2) i (2) ( ω i ) = ε 0 χijk ( ωi, ω j, ωk ) E j ( ω j ) Ek ( ωk ) jk ω + ω + ω = 0 30 i j k

16 The ground state uncertainty is squeezed, when the pump field shows a minimum, Parametric amplification (degenerate): Graphical description how the ground state uncertainty is converted into a squeezed vacuum [J. Bauchrowitz, T. Westphal, R.S., Am. J. Phys. 81, 767 (2013)] 31 Wigner Function of Squeezed Light Phase-space quasiprobability distribution of a squeezed vacuum state Measured: db / +16 db@5mhz [Mehmet et al., PRA 81, (2010)] 32

17 The GEO600 Squeezed Light Laser [H. Vahlbruch, A. Khalaidovski, N. Lastzka, C. Gräf, K. Danzmann, and R. Schnabel, The GEO600 squeezed light source, Class. Quantum Grav. 27, (2010)] Alexander Khalaidovski: Stefano Braccini Thesis Prize Transport to the GEO600 GW Detector 34

18 GEO600 Spectral Density 2010 Observatory noise, calibrated to GW-strain [1/ Hz] k Frequency [Hz] Photon shot noise (Poisson statistics) 2k 3k 4k 5k 35 GEO600: Squeezed Light in Application Observatory noise, calibrated to GW-strain [1/ Hz] k 2k Frequency [Hz] Observatory noise without squeezed light Observatory noise with 10 db squeezing (and 38% loss) Optimum quantum approach! [Demkowicz-Dobrzanski, Banaszek, Schnabel, PRA 88, (R) 3k 4k (2013)] 5k 36

19 This is not just a proof of principle! Shot noise squeezed GEO600 regularly uses squeezed light during its observational runs. [Grote et al., PRL 110, (2013)] An application of nonclassical quantum metrology today! 37 LSC, Nature Photonics 7, (2013) 38

20 Shot Noise and Radiation Pressure Noise [Caves 1981] Shot noise Quantum noise in phase quadrature (Both signal Normalized) Radiation pressure noise Squeezed shot noise, 20dB (Alternatively 100x laser power) Standard quantum limit (SQL) 39 Shot Noise and Radiation Pressure Noise [Caves, Phys. Rev. D 45, 75 (1980)] (Light power, coherent state) 40

21 Squeezing SN and RPN [Jaekel, Reynaud 1990] ˆ X 2 Shot noise QND- Regime Radiation pressure noise ˆ X 1 Squeezed Light Input (8dB) Standard Quantum Limit (SQL) 41 Gravitational-Wave Detection Mirror 1 1) Quasi-free test mass mirrors 2) Laser light α Laser ~ km Mirror 2 3) Interference Photo diode GW induced distance change 4) Photo-electric effect Photo-electric current modulated at GW frequency ( unbiased estimator ) 42

22 Calibration of Photo Diode Quantum Efficiency Total Efficiency: (97.5 ± 0.1)% à PD: (99.5 ± 0.5)% 99.8% (99.05 ± 0.45)% [H. Vahlbruch, MM, KD, RS, Phys. Rev. Lett., accepted (2016)] 43 The Einstein Telescope 10 km arms under ground Cryo-cooled silicon mirrors 10 db squeezed light at 1064 nm and 1550 nm European design study [M. Punturo et al., Class. Quantum Grav (2010)] 44

23 Summary / Outlook Squeezed light can be used to calibrate photo detectors The GW detector GEO600 uses squeezed light in observational runs. Most likely, squeezed light will be used in all future GW detectors. The nonclassical (paradoxical) part of quantum mechanics will improve the detection of gravitational waves. 45