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Quantum noise reduction techniques for the Einstein telescope

This paper explores various quantum noise reduction techniques for the Einstein Telescope, a next-generation gravitational wave detector. The goal is to significantly improve sensitivity and reduce noise in order to detect frequencies as low as a few Hz. The paper discusses the requirements for the detector's sensitivity, the classical noise budget, and different quantum noise reduction options.

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Quantum noise reduction techniques for the Einstein telescope

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  1. Quantum noise reduction techniques for the Einstein telescope Helge Müller-Ebhardt on behalf of ET WG3 Max-Planck-Institut für Gravitationsphysik (AEI) and Leibniz Universität Hannover TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: AAAA

  2. 1st generation 2nd generation 3rd generation Requirements on the sensitivity for ET • a hundred times better sensitivity than initial detectors • significantly increase the detection band towards frequencies as low as a few Hz • highly broadband • extremely sensitive -19 10 Seismic -20 10 -21 10 -22 Noise Spectral Density 10 shot noise thermal noise -23 10 [Punturo, 2008] -24 10 -25 10 1 10 100 1000 10000 f [Hz]

  3. ET’s classical noise budget • detector with 10 km long arms of few hundred kg test-mass mirrors • underground facility with long tunnel system and high caverns • cryogenic environment for test-masses and suspension system • up scaled super attenuator • Newtonian noise subtraction [Hild, 2010]

  4. Simple position meter: Michelson interferometer • detector with 10 km long arms of few hundred kg test-mass mirrors • power-recycling and arm cavities increase circulating optical power • finite arm-cavity bandwidth → shot noise rises at high frequencies • tuned signal-recycling → effective bandwidth • quantum noise touches SQL (depending on optical power)

  5. Overview: quantum noise reduction options • optical-spring interferometer • speed-meter interferometer • optical inertia interferometer • optical transducer with local readout • (frequency-dependent) input-squeezing interferometer • variational-output interferometer single interferometer detector ↔ xylophone detector

  6. QNR technique: optical-spring interferometer • Michelson interferometer with detuned signal-recycling cavity • optomechanical coupling induces a restoring force acting on test-masses: optical spring • mechanical resonance up-shifted into detection band • sensitivity enhanced around resonances • well-investigated in prototypes and table-top experiments

  7. QNR technique: speed-meter interferometer • different optical realizations proposed: sloshing cavity, polarizing optics, Sagnac topology, long signal-recycling cavity, … • frequency-independent back-action noise at low frequencies is cancelled in output → shot noise limited • SQL beating depends on optical power / cavity bandwidth • combinable with frequency-dependent input squeezing • speed meter effect not yet experimentally observed • technical challenges: ring cavities,... [Chen, 2003] [Purdue, 2002] [Danilishin, 2004]

  8. QNR technique: input-squeezing • squeezed vacuum input at dark port increases sensitivity • optimal frequency-dependent squeezing ellipse → overall sensitivity enhancement • squeezed field reflected at filter cavities realizes frequency dependency • 2 filter cavities required for e.g. optical-spring interferometer • optical loss in filter cavities degenerates squeezing → sets requirements on filter cavities • well-investigated technique

  9. QNR technique: variational output • at every frequency there exists optimal readout quadrature • output field reflected at filter cavities → frequency-dependent readout quadrature • 2 filter cavities required for e.g. optical-spring interferometer • quadrature without signal content in output → optical loss increases noise and decreases signal • highly susceptible to optical loss • technique less investigated

  10. Single interferometer detector: Michelson frequency-dependent input-squeezing 300 ppm loss in two 10 km (1 km) long filter cavities • circulating optical power 3 MW • arm length 10 km • test-mass mirror weight 120 kg variational output 20 ppm loss in two 10 km (1 km) long filter cavities

  11. Single interferometer detector: Sagnac frequency-dependent input-squeezing 300 ppm loss in two 10 km (1 km) long filter cavities • circulating optical power 3 MW • arm length 10 km • test-mass mirror weight 120 kg variational output 20 ppm loss in two 10 km (1 km) long filter cavities

  12. Two-band xylophone detector • hard to realize broadband single interferometer detector - in terms of quantum noise, especially optical loss - in terms of technical noise even more • split detection band into LF interferometer and HF interferometer • LF interferometer: - up scaled advanced detector - cold - optical-spring • HF interferometer: - up scaled initial detector - room-temperate - high-power [Hild, 2010]

  13. LF interferometer: filter cavities vs. Sagnac • Sagnac interferometer with frequency-independent input squeezing - no filter cavities - need ring cavities in the arms - moderate test-mass weight possible - moderate circulating optical power (180 kW) • optical-spring interferometer with frequency-dependent input squeezing - need filter cavities - heavy test-mass mirrors - low circulating optical power (18 kW) ET-LF option

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