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Approaching the quantum limit with a new read-out on EXPLORER and NAUTILUS: 

Approaching the quantum limit with a new read-out on EXPLORER and NAUTILUS Alessio Rocchi University of Rome “Tor Vergata” and INFN Roma 2 for the ROG Collaboration 6th Edoardo Amaldi Conference on Gravitational Waves Okinawa, June 20-24, 2005 www.lnf.infn.it/esperimenti/rog Alessio.Rocchi@lnf.infn.it

Slide2: 

MiniGrail INFN Frascati CERN RE 5

Slide3: 

EXPLORER and NAUTILUS Duty cycle more than 90% <Tnoise>NAU = 2 mK h = 3 10-19 10-4 Mo at Galactic Centre Strain sensitivity of EXPLORER and NAUTILUS Talk by M. Visco this morning Single gap transducers (gap ≈ 10μm) and single-stage dc SQUIDS (ε ≈ few thousand ħ)

Slide4: 

β, transduction efficiency Tn, noise temperature

Double-gap transducer: 

Double-gap transducer Actual gap on NAUTILUS transducer ≈ 9μm

Preliminary results on the Double-gap transducer: 

Preliminary results on the Double-gap transducer Minenkov, J. Phys. D: Appl. Phys. 33, 1134–1136 (2000) @ T=4.2 K, Q = 1.5·106, Upol ≈ 200 V gap ≈ 10 μm gap ≈ 20 μm

Slide7: 

The ROG 2-stage SQUID amplifier Quantum Design dc SQUID ROG dc SQUID Carelli et al., Appl. Phys. Lett. 72, 115 (1998)

Slide8: 

Open input noise measurement of the ROG 2-stage SQUID amplifier Energy resolution  30ħ around 1kHz @ 4.2K

Slide9: 

High-Q input circuit (L0=96mH, Q0=0.7·106, k=0.38). f0= 1740 Hz Lf 300K 4.2K 1 see Vinante et al., Physica C 368, 176-180 (2002) Working point stabilization via cold-damping network1

Slide10: 

Energy resolution vs temperature @ T=2.0 K, the flux noise is 0.21μΦ0/√Hz corresponding to 70ħ

Slide11: 

Next Steps Investigate temperatures below 2 K; Increase the transformer coupling; Measurement of back-action to estimate noise temperature Tn; Couple the system to the double gap transducer.

Slide12: 

Expected Sh for NAUTILUS @ 0.12K, double gap transducer (11 μm and Q=1.5·106) and double SQUID (L0=2.5 H, k=0.7, Φn= 0.16μΦ0/√Hz). Teff ≈ 7μK (corresponding to h=2.1·10-20), sensitivity < 1·10-21 /√Hz over 35Hz. 3·10-22

Slide15: 

Carelli et al. 98