6th Edoardo Amaldi Conference on Gravitational WavesOkinawa, June 20-24, 2005

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

Alessio RocchiUniversity of Rome “Tor Vergata” and INFN Roma 2for the ROG Collaboration

www.lnf.infn.it/esperimenti/rogAlessio.Rocchi@lnf.infn.it

21st June 2005 Amaldi 6 - Alessio Rocchi

MiniGrail

INFN Frascati

CERN RE 5

21st June 2005 Amaldi 6 - Alessio Rocchi

EXPLORER and NAUTILUSDuty cycle more than 90%

<Tnoise>NAU = 2 mKh = 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)

21st June 2005 Amaldi 6 - Alessio Rocchi

β, transduction efficiency Tn, noise temperature

nTf β∝∆ nB

BeffB Tk

QTkTkE 2min +≈=∆

β

21st June 2005 Amaldi 6 - Alessio Rocchi

Double-gap transducer

Actual gap on NAUTILUS transducer ≈ 9µm

21st June 2005 Amaldi 6 - Alessio Rocchi

Preliminary results on the Double-gap transducerMinenkov, J. Phys. D: Appl. Phys. 33, 1134–1136 (2000)

gap ≈ 20 µm

@ T=4.2 K, Q = 1.5·106, Upol ≈ 200 Vgap ≈ 10 µm

21st June 2005 Amaldi 6 - Alessio Rocchi

The ROG 2-stage SQUID amplifier

Quantum Design dc SQUIDROG dc SQUID

Carelli et al., Appl. Phys. Lett. 72, 115 (1998)

21st June 2005 Amaldi 6 - Alessio Rocchi

Open input noise measurement of the ROG 2-stage SQUID amplifier

0,01

0,1

1

10

100 1000 104 105

Power spectrum density

Frequency (Hz)

Energy resolution ≈ 30ħaround 1kHz @ 4.2K

-0,015

-0,01

-0,005

0

0,005

0,01

0,015

-0,1 0 0,1 0,2 0,3 0,4

V

Φ0

21st June 2005 Amaldi 6 - Alessio Rocchi

Working point stabilization via cold-damping network1

300K

Lf

4.2K

High-Q input circuit (L0=96mH, Q0=0.7·106, k=0.38). f0= 1740 Hz

1 see Vinante et al., Physica C 368, 176-180 (2002)

21st June 2005 Amaldi 6 - Alessio Rocchi

Energy resolution vs temperature

0

50

100

150

200

0 1 2 3 4 5

N

T (K)

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

21st June 2005 Amaldi 6 - Alessio Rocchi

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.

21st June 2005 Amaldi 6 - Alessio Rocchi

10-22

10-21

10-20

850 900 950 1000

Stra

in s

ensi

tivity

(Hz-1

/2)

Frequency (Hz)

3·10-22

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.

21st June 2005 Amaldi 6 - Alessio Rocchi

21st June 2005 Amaldi 6 - Alessio Rocchi

0

100

200

300

400

500

600

0 1 2 3 4 5

N ROGN MiniGrailN AURIGA

N

T (K)

21st June 2005 Amaldi 6 - Alessio Rocchi

10-2 10-1 100 101 102 103 10410-8

10-7

10-6

10-5

Experimental flux noise spectral density of the Rome double stage SQUID amplifier

= 5.5 h

=28 h

ε

ε

T= 0.9 K

T=4.2 K

frequency (Hz)

Φn

(Φ0

/√H

z)

2

2

2ML ninΦ=ε

Carelli et al. 98