Magnetic Flux Noise in dc SQUIDs: Temperature and Geometry Dependence

Anton, Steven; Birenbaum, Jeffrey; O'Kelley, Sean; Bolkhovsky, Vladimir; Braje, Danielle; Fitch, George; Neeley, M.; Hilton, G. C.; Cho, H.-M.; Irwin, K. D.; Wellstood, F. C.; Oliver, William; Shnirman, Alexander; Clarke, John

doi:10.1103/physrevlett.110.147002

Cited by 95 publications

(101 citation statements)

References 30 publications

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“…We predict the presence of a crossing band supported by Ref. 12 and present additional experimental measurements of flux noise in superconducting flux qubits in a temperature range between 20 and 80 mK that confirm this prediction. The model allows us to use these measurements to estimate the spin-diffusion constant and explore its dependence on temperature.…”

Section: Introductionsupporting

confidence: 69%

“…12 We presented experimental data in the low temperature range (T = 20 − 80 mK), showing that the theory can explain the experiments provided that we assume that the spin-diffusion constant increases with temperature. A temperature dependent spin diffusion constant suggests that the spin system is close to a spinglass phase transition, but more experiments are needed to confirm this assertion.…”

Section: Discussionmentioning

confidence: 99%

“…The dashed line shows the fitting function used in Eq. (12). Inset: A zoom into the crossing band region at f0.…”

Section: Frequency and Temperature Dependence Of Flux Noisementioning

confidence: 99%

“…Since spin-lattice relaxation is suppressed at low temperatures, 8 it was proposed that the RKKY interaction between spins is responsible for spin-diffusion and flux noise; 10 however their theory of spin-diffusion predicted 1/f noise independent of temperature, thus it does not explain the frequency and temperature dependence of flux noise observed in SQUIDs. 11,12 Anton et al 12 recently presented a comprehensive experiment that seemed to contradict the spin-diffusion interpretation; they measured flux noise above T = 100 mK and proposed a power law fit of the form A 2 /f α , showing that the temperature dependence of A and α leads to the presence of a pivot frequency, below (above) which the noise decreases (increases) with increasing temperature.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for temperature-dependent spin diffusion as a mechanism of intrinsic flux noise in SQUIDs

et al. 2014

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The intrinsic flux noise observed in superconducting quantum interference devices (SQUIDs) is thought to be due to the fluctuation of electron spin impurities, but the frequency and temperature dependence observed in experiments do not agree with the usual 1/f models. We present theoretical calculations and experimental measurements of flux noise in rf-SQUID flux qubits that show how these observations, and previous reported measurements, can be interpreted in terms of a spindiffusion constant that increases with temperature. We fit measurements of flux noise in sixteen devices, taken in the 20 − 80 mK temperature range, to the spin-diffusion model. This allowed us to extract the spin-diffusion constant and its temperature dependence, suggesting that the spin system is close to a spin-glass phase transition.

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Section: Introductionsupporting

confidence: 69%

Section: Discussionmentioning

confidence: 99%

“…The dashed line shows the fitting function used in Eq. (12). Inset: A zoom into the crossing band region at f0.…”

Section: Frequency and Temperature Dependence Of Flux Noisementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evidence for temperature-dependent spin diffusion as a mechanism of intrinsic flux noise in SQUIDs

et al. 2014

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“…This effect can be attributed to the larger electric fields near metallic surfaces and the higher concentration of two-level systems (TLS) at disordered interfaces 5-7 . At the same time, magnetic impurities at the surface of superconductors have been proposed as the cause of 1/f flux noise that limits the performance of SQUID based qubits and sensors [8][9][10] .In order to better understand these effects, one strategy is to drastically alter the geometry of materials and interfaces that contribute to qubit loss and decoherence. In this Letter, we present a procedure for removing the substrate and suspending aluminum Josephson junctions on silicon by micromachining.…”

mentioning

confidence: 99%

Suspending superconducting qubits by silicon micromachining

Chu

Axline

Wang

et al. 2016

Applied Physics Letters

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We present a method for relieving aluminum 3D transmon qubits from a silicon substrate using micromachining. Our technique is a high yield, one-step deep reactive ion etch that requires no additional fabrication processes, and results in the suspension of the junction area and edges of the aluminum film. The drastic change in the device geometry affects both the dielectric and flux noise environment experienced by the qubit. In particular, the participation ratios of various dielectric interfaces are significantly modified, and suspended qubits exhibited longer T 1 's than non-suspended ones. We also find that suspension increases the flux noise experienced by tunable SQUID-based qubits.The coherence times of superconducting qubits have steadily increased over the past decade due to careful engineering of the electromagnetic environment, better materials and fabrication methods, and improved device designs that minimize loss. State-of-the-art superconducting qubits with the longest lifetimes (T 1 ) make use of very low loss tangent dielectric substrates and have large separation between planar conductors to decrease the effect of dielectric loss in the interfaces between materials 1-3 . In particular, it has been shown that for aluminum 3D transmons on sapphire, T 1 times are limited by the various interfaces between the dielectric substrate, the superconducting metal, and vacuum 4 . This effect can be attributed to the larger electric fields near metallic surfaces and the higher concentration of two-level systems (TLS) at disordered interfaces 5-7 . At the same time, magnetic impurities at the surface of superconductors have been proposed as the cause of 1/f flux noise that limits the performance of SQUID based qubits and sensors [8][9][10] .In order to better understand these effects, one strategy is to drastically alter the geometry of materials and interfaces that contribute to qubit loss and decoherence. In this Letter, we present a procedure for removing the substrate and suspending aluminum Josephson junctions on silicon by micromachining. Silicon is a low-loss dielectric that offers several advantages for implementing the next generation of complex quantum circuits 11,12 . Its prevalent use in the semiconductor and MEMS industries have led to a large variety of fabrication techniques that are not available for sapphire 13 . Using silicon as a substrate material enables the development of novel devices and architectures in circuit QED, such as multilayer quantum circuits that incorporate micromachined superconducting enclosures and resonators 14,15 . Substrate micromachining has also been used to reduce dielectric loss and frequency noise in niobium titanium nitride coplanar waveguide resonators on silicon 16,17 . On the other hand, silicon has a more complex surface chemistry than sapphire; for example, it forms an amorphous oxide layer a) Electronic mail: yiwen.chu@yale.edu that may be host to a large number of TLS's and paramagnetic impurities 11,18,19 .We suspend our qubits with a simple, one-step dee...

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