Thermal noise in a high Q ultracryogenic resonator

Vinante, Andrea; Mezzena, R.; Prodi, G. A.; Vitale, S.; Cerdonio, M.; Bonaldi, M.; Falferi, P.

doi:10.1063/1.1947927

Cited by 10 publications

(6 citation statements)

References 16 publications

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“…Other experimental details on the realization of the low loss resonator and its housing are reported in a previous paper. 9 The expected resonance frequency, considering also the coupling to the SQUID, is about 11 kHz. We have chosen to operate at this frequency instead of around 1 kHz, the typical operation frequency of the present resonant gravitational wave detectors, for two reasons: First, to enhance the SQUID back action noise, which increases with the square of the frequency, over the resonator thermal noise; second, at 11 kHz the seismic and ambient vibrational noise are negligible in our experimental conditions.…”

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confidence: 99%

27 ℏ SQUID amplifier operating with high-Q resonant input load

Falferi

Bonaldi

Cerdonio

et al. 2006

Applied Physics Letters

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We have extended to ultracryogenic temperatures the complete noise characterization of a low-noise two-stage superconducting quantum interference device (SQUID) amplifier developed for resonant gravitational wave detectors. The additive current noise is evaluated from open input measurements. To evaluate the back action voltage noise, the SQUID is strongly coupled to a high-Q macroscopic electrical resonator operating at 11.7 kHz. From these measurements, we estimate a minimum noise temperature of 15μK, corresponding to 27 times the quantum-limited noise temperature. Implications of this result for the sensitivity of resonant gravitational wave detectors are briefly discussed.

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confidence: 99%

27 ℏ SQUID amplifier operating with high-Q resonant input load

Falferi

Bonaldi

Cerdonio

et al. 2006

Applied Physics Letters

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“…At 59 mK both SQUID and resistor holder are placed inside a copper box, in good thermal contact with the mixing chamber of a dilution refrigerator [10]. The box is filled with 1 atm of 4 He gas at room temperature to improve thermalization of the internal elements.…”

Section: Introductionmentioning

confidence: 99%

Cooling fins to limit the hot-electron effect in dc SQUIDs

Falferi

Mezzena

Vinante

2008

J. Phys.: Conf. Ser.

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Abstract. The generally accepted noise theory of the dc SQUID predicts that the energy resolution scales as the electron temperature in the Josephson junction shunt resistors. As in metals at low temperature the electron-phonon coupling becomes very weak, the electron gas of the thin film shunt resistors undergoes a Joule heating due to the bias current and its temperature can be significantly higher than that of the thermal bath. This heating, the hotelectron effect, causes a deviation from the linear behaviour of noise versus temperature and a saturation of the SQUID noise, typically at temperatures of about 200 mK. This effect can be reduced considerably by increasing the effective volume available for the electron-phonon interaction by attaching "large" cooling fins to the shunt resistors. Our measurements have been performed on two thin film devices made with the same design of a dc SQUID but without the Josephson junctions: one device with standard shunt resistors, the other with shunt resistors with cooling fins. From these measurements one can expect for the SQUID with cooling fins an improvement of the noise saturation temperature of at most a factor 2, from 200 mK to about 100 mK. IntroductionThe noise characteristics of the low-T c dc SQUID are well-explained by the resistively-and capacitively-shunted junction (RCSJ) model [1] in which a Nyquist current noise source is associated to each of the two shunt resistances R that are necessary to avoid hysteresis in the I-V characteristic of the Josephson junctions. This model predicts [2] for a dc SQUID under optimum conditions an energy resolution ε=S Φ /2L=9k B TL/R=16k B T(LC) 1/2 where S Φ is the flux noise spectral density, L is the SQUID loop inductance and C is the capacitance of each junction. The white noise of a large number of SQUIDs has been found in good agreement with these predictions. Although quoting this white noise (and the associated energy resolution) is not sufficient to completely characterize the SQUID noise (in fact one has to consider also the 1/f noise and the back action current noise in the SQUID loop) it is usually taken as an indication of the sensitivity of the device.In most experiments in which the SQUID is employed as the front-end amplifier, its noise is one of the parameters that limit the sensitivity of the measurement (see, for example [3]). Besides optimizing the geometrical parameters of the SQUID (low SQUID loop inductance and low junction capacitance)

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“…The superconducting transformer is housed in a separate superconducting SnPb electroplated copper box, attached to the transducer by means of decoupling suspensions. The transformer has a very high geometrical coupling factor k = M/ √ LL s = 0.86, and very small stray capacitance, of order 10 pF, obtained by means of a multisector primary coil [12]. Two separate boxes, also vibrationally decoupled by means of calibrated suspensions, house respectively the decoupling PTFE Teflon capacitor C d and the cryogenic switch.…”

Section: Methodsmentioning

confidence: 99%

“…A temperature of 100 mK, as in the first AURIGA run, is a reasonable target. The 100 mK curves in figure 3 are obtained by assuming that Q-factors do not depend on temperature, and that electrical noise and mechanical noise scale with T. As regards the electrical noise, the scaling of the thermal noise in a high-Q resonator at ultracryogenic temperature has already been demonstrated [12]. Finally, the SQUID noise is assumed to saturate at a temperature of 200 mK, as observed in separate bench tests [13].…”

Section: Present Performance and Future Upgradesmentioning

confidence: 95%

Present performance and future upgrades of the AURIGA capacitive readout

Vinante

2006

Class. Quantum Grav.

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The resonant bar gravitational wave detector AURIGA is taking data for its second run at T = 4.5 K. The readout has been largely upgraded with respect to the previous run. In particular, we have realized a 3-mode detection scheme by tuning the high-Q resonance of the electrical readout to the mechanical modes of bar and transducer. Moreover, a low noise two-stage SQUID amplifier has been implemented. Thanks to these improvements, the bandwidth has been largely increased and the strain sensitivity is now better than 10 −20 Hz −1/2 over more than 100 Hz. In this paper, we describe a 3-mode model of the detector, which allows us to distinguish between the different noise contributions. Some possible upgrades are discussed.

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Thermal noise in a high Q ultracryogenic resonator

Cited by 10 publications

References 16 publications

27 ℏ SQUID amplifier operating with high-Q resonant input load

27 ℏ SQUID amplifier operating with high-Q resonant input load

Cooling fins to limit the hot-electron effect in dc SQUIDs

Present performance and future upgrades of the AURIGA capacitive readout

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