Investigation of Low-Frequency Excess Flux Noise in DC SQUIDs at mK Temperatures

Drung, D.; Beyer, J.; Storm, Jan-Hendrik; Peters, M.; Schurig, T.

doi:10.1109/tasc.2010.2084054

Cited by 23 publications

(28 citation statements)

References 22 publications

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“…Fits of S È ðfÞ for (b) SQUID I.1 at 10 temperatures and (c) SQUID II.upturn for T < 0:15 K, and increases monotonically with R. In contrast, for chip II A 2 becomes independent of T for T & 0:6 K, a result reminiscent of the findings of Wellstood et al[18]. With regard to the slope, for both chips increases dramatically as T is lowered from 4.0 to 0.1 K. For chip I, the value of increases with R. Similarly low values of , 0.4-0.5 at 4 K, have been observed by other authors[17,28]. Although we have no explanation for the disparate dependencies of A 2 and on T, we remark that for chip I W is constant at 0:5 m while for chip II W varies from 15 to 240 m. A conceivable explanation is that interactions between spins give rise to spatial correlations.The progressive increase in as T is lowered is illustrated vividly in Figs.…”

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confidence: 81%

“…Here, È is flux and & 1. Flux noise is a major source of intrinsic dephasing [7] in superconducting flux [8][9][10][11][12] and phase qubits [7,13,14] and in the quantronium [15]; it also generates low-frequency noise in SQUIDs [16][17][18].It has been proposed that flux noise originates from the random reversal of spins at the interfaces between the superconductor and its substrate and surface oxide layer [19][20][21]. Models that assume independent spins with a magnetic moment B (the Bohr magneton) predict an areal spin density of 5 Â 10 17 m À2 .…”

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confidence: 99%

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confidence: 99%

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Magnetic Flux Noise in dc SQUIDs: Temperature and Geometry Dependence

et al. 2013

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The spectral density S(Φ)(f) = A(2)/(f/1 Hz)(α) of magnetic flux noise in ten dc superconducting quantum interference devices (SQUIDs) with systematically varied geometries shows that α increases as the temperature is lowered; in so doing, each spectrum pivots about a nearly constant frequency. The mean-square flux noise, inferred by integrating the power spectra, grows rapidly with temperature and at a given temperature is approximately independent of the outer dimension of a given SQUID. These results are incompatible with a model based on the random reversal of independent, surface spins.

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confidence: 81%

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Magnetic Flux Noise in dc SQUIDs: Temperature and Geometry Dependence

et al. 2013

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“…Low-frequency excess noise, which does neither arise from I 0 nor from vortex fluctuations, has been reported during the last decades for SQUIDs based on conventional superconductors like Nb, Pb, PbIn and Al, in particular at temperatures well below 1 K 45 . This issue has recently been revived due to the increasing interest in the development of flux qubits and SQUIDs for ultralow temperature applications 46 . Various models have been suggested to describe the origin of such low-f excess noise, e.g.…”

Section: Fll Mode: DC Bias Vs Bias Reversalmentioning

confidence: 99%

Low-NoiseYBa2Cu3O7Nano-SQUIDs for Performing Magnetization-Reversal Measurements on Magnetic

et al. 2015

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We fabricated YBa2Cu3O7 (YBCO) direct current (dc) nano superconducting quantum interference devices (nanoSQUIDs) based on grain boundary Josephson junctions by focused ion beam patterning. Characterization of electric transport and noise properties at 4.2 K in magnetically shielded environment yields a very small inductance L of a few pH for an optimized device geometry. This in turn results in very low values of flux noise < 50 nΦ0/Hz 1/2 in the thermal white noise limit, which yields spin sensitivities of a few µB/Hz 1/2 (Φ0 is the magnetic flux quantum and µB is the Bohr magneton). We observe frequency-dependent excess noise up to 7 MHz, which can only partially be eliminated by bias reversal readout. This indicates the presence of fluctuators of unknown origin, possibly related to defect-induced spins in the SrTiO3 substrate. We demonstrate the potential of using YBCO nanoSQUIDs for the investigation of small spin systems, by placing a 39 nm diameter Fe nanowire, encapsulated in a carbon nanotube, on top of a non-optimized YBCO nanoSQUID and by measuring the magnetization reversal of the Fe nanowire via the change of magnetic flux coupled to the nanoSQUID. The measured flux signals upon magnetization reversal of the Fe nanowire are in very good agreement with estimated values, and the determined switching fields indicate magnetization reversal of the nanowire via curling mode.

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“…In the last decade similar effect has been observed in nanoscale quantum circuits [12][13][14][15][16][17][18][19][20][21][22][23] . Remarkably, the noise magnitude appears to be "universal", i.e., of the same order of magnitude for a wide range of device sizes.…”

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confidence: 55%

Nonequilibrium spin noise and noise of susceptibility

et al. 2014

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We analyze out-of-equilibrium fluctuations in a driven spin system and relate them to the noise of spin susceptibility. In the spirit of the linear response theory we further relate the noise of susceptibility to a 4-spin correlation function in equilibrium. We show that, in contrast to the second noise (noise of noise), the noise of susceptibility is a direct measure of non-Gaussian fluctuations in the system. We develop a general framework for calculating the noise of susceptibility using the Majorana representation of spin-1/2 operators. We illustrate our approach by a simple example of non-interacting spins coupled to a dissipative (Ohmic) bath.PACS numbers: 85.25. Dq, 85.25.Am Noise in electronic circuits provides information about the microscopic structure of the system complementary to that obtained from linear response transport measurements 1,2 . For electronic circuits, the standard JohnsonNyquist noise is intimately related to dissipative processes with typical time scales of the order of picoseconds. At low frequencies it is "white", i.e. frequencyindependent. In contrast, the ubiquitous 1/f noise is related to slow processes, e.g., to slow rearrangements of impurities or the internal dynamics of two-level systems 3 . Its power spectrum is commonly described by the Hooge's law 4,5 , S V (f ) ∝ V 2 /f , where V is the average observed voltage. This suggests that this noise could only be observed out of equilibrium. But this was shown not to be the case by Voss and Clarke 6,7 , who measured the low-frequency fluctuations of the mean-square Johnson voltage in equilibrium (i.e., the second noise or noise of noise) and showed that these fluctuations possess a 1/f -like spectrum.Motivated by these experiments, Beck and Spruit 8 calculated the variance of the Johnson-Nyquist noise and showed that it comprised two contributions. The first one could be interpreted as arising from resistance fluctuations with a 1/f spectrum. The second, with a white spectrum, is intrinsic to any Gaussian fluctuating quantity. Consequently the equilibrium 1/f noise could only be observed at very low frequencies.From a technical point of view the variance of noise is described by a four-point correlation function 1,8 . Such objects appear also in other physical contexts. For example, Weissman 9,10 has proposed to distinguish the droplet and hierarchical models of spin glasses by the properties of the second noise, which can be expressed in terms of a particular four-spin correlation function.More recently, the problem of 1/f noise has attracted much attention in the field of superconducting quantum devices. Flux noise measurements initially performed with relatively large SQUIDs showed the 1/f behavior 11 .In the last decade similar effect has been observed in nanoscale quantum circuits 12-23 . Remarkably, the noise magnitude appears to be "universal", i.e., of the same order of magnitude for a wide range of device sizes. This noise is believed to originate from an assemblage of spins localized at the surface or interface lay...

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Investigation of Low-Frequency Excess Flux Noise in DC SQUIDs at mK Temperatures

Cited by 23 publications

References 22 publications

Magnetic Flux Noise in dc SQUIDs: Temperature and Geometry Dependence

Magnetic Flux Noise in dc SQUIDs: Temperature and Geometry Dependence

Low-NoiseYBa2Cu3O7Nano-SQUIDs for Performing Magnetization-Reversal Measurements on Magnetic

Nonequilibrium spin noise and noise of susceptibility

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