La réduction du bruit quantique Pierre-François Cohadon (avec Sheon Chua et l’équipe du LKB)

Quantum Noise and Measurement back-action

Quantum Noise in GW Detection Quantum Noise is a limiting noise source Shot Noise ∝1/√𝑃 Radiation Pressure Noise ∝ 𝑃 Crossover at SQL Frequency Due to opposite dependency, changing power moves the QN curve along the SQL curve Options to increase sensitivity Reduce the amount of noise: Frequency Independent Squeezing: O3 Frequency Dependent Squeezing: O4 Noise-independent measurement: Variational Readout Independent measurement and feedforward: EPR Entanglement

Variational Readout (circa 2002) GW signal RP noise  mechanical response /M2) Shot noise Amplitude noise

Variational Readout (circa 2002) GW signal RP noise  mechanical response /M2) Shot noise Amplitude noise Monitoring a different quadrature allows to cancel RP noise, but the quadrature depends on c: frequency-dependent detection required!

Variational Readout (circa 2002) Pros: Large gain in low-f sensitivity, larger than applied optimal squeezing Compatible with standard (non-FDS) squeezing injection also Cons: Not demonstrated for GWD Two long cavities needed, regardless of GWD configuration (Broadband, Tuned etc) Substantial change to GWD readout No further development planned as of now – future?

EPR-Entanglement for FDS (circa 2015) Pros: Additional long cavities not needed Cons: No experimental demonstration (yet) 3 dB less gain w.r.t. current techniques New ITF readout scheme needed (Local Oscillators) Considered only an AdV+ potential technology Included in the “AdV+ Roadmap” document Brown et al Ma et al

Frequency-Independent Squeezing (circa 1980) Pros: Well tested method for GWD (LIGO, GEO600) Equivalent of changing power Largely standalone system Cons: Potential sensitivity loss due to impact of Anti-Squeezing LIGO 2013

O3 AdV: FIS December 2016, AEI offered Virgo an in-air frequency-independent squeezer, under preparation since early 2015 Goal: Up to 4dB increase in sensitivity at higher frequencies without decreasing low-frequency sensitivity too much A. Bertolini (Nikhef) H. Vahlbruch, M. Mehmet (AEI)

O3 AdV: FIS Hosting of the AEI Squeezer in DET Cleanroom Area Squeezer installed: mode-matching, commissioning in progress New vacuum flanges R.Gouaty (LAPP) Steel rigid frame on simple elastomer pads. A. Bertolini (Nikhef) Acoustic enclosure F. Carbognani (EGO)

FDS: Using FIS with a Filter Cavity Use the phase response of a “Filter Cavity” to rotate the squeezing ellipse as a function of frequency One Filter Cavity is sufficient for ellipse rotation for GWD in the broadband tuned-signal recycling case. Detuned SR needs two cavities FIS + Filter Cavity

FDS: Using FIS with a Filter Cavity Pros: Tested and demonstrated method (next slide) Compatible with current GWD readout Largely standalone system to the ITF Cons: Needs the additional Filter Cavity, with linewidth matching SQL crossover of ~ 50 Hz

FDS with Filter Cavities around the World First demonstrated in 2005 in MHz (AEI) Theoretical studies into designs, optical loss requirements (2003 to present) Audio-band demonstration 2016 (MIT, ANU) Setups coming online in 2018 TAMA (NAOJ, APC, Nikhef) CALVA at LAL Orsay (with LKB,LMA and LAPP) S. Chelkowski et al E. Oelker et al E. Capocasa et al

O4 AdV: FDS with Filter Cavity Preliminary Conceptual Design work started To lead to WBS and FDS TDR Authors for the Conceptual Design sections listed below A. Bertolini (Nikhef) Now included in the “Future of AdV” or “AdV+ Roadmap” document Sensitivity Curves: A. Bertolini, S. Chua, R. Flaminio, J. P. Zendri Filter cavity (optics): M. Tacca, M. Barsuglia, M. De Laurentis, P. Gruning, J. Degallaix, R. Flaminio, R. Bonnand Filter Cavity (vacuum system): B. Mours, A .Bertolini Squeezing source: S.Chua, H.Vahlbruch, E. Genin, R.Bonnand Backscattering: L. Conti, A. Bertolini, S. Chua

O4 AdV: FDS with Filter Cavity Preliminary Infrastructure Conceptual Design (LAPP, Nikhef) New meetings past

O4 AdV: FDS with Filter Cavity Squeezed Light Source (LKB, AEI, EGO) : In-air or In-vacuum As of today: Decision to wait on the various GWD squeezing experiments coming online in the next 6 months Squeezing Mini-tower is needed for both configurations

O4 AdV: FDS with Filter Cavity The “AdV+ Roadmap” document builds on the Preliminary FDS Conceptual Design work. However, perhaps the final Conceptual Design will have impact from the Roadmap Document Considerations for “AdV+ Roadmap” Document Chapter on FDS to finalise: Decision on Filter Cavity length Decision on residual pressure in the Filter Cavity tanks Changes needed to SDB1 in O4 Timeline Costs

Summary Squeezing is (now) considered an important upgrade of AdV First step: FIS for O3 with AEI squeezer Squeezer delivered early 2018 Installation/Commissioning in progress Next step : FDS Planned for 04 A number of pending decisions, including in-air or in-vacuum squeezer ExSqueez project between LAL, LMA, LAPP and LKB to gain expertise