<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mi>f</mml:mi></mml:math>Flux Noise in Josephson Phase Qubits

Bialczak, Radoslaw C.; McDermott, Robert; Ansmann, M.; Hofheinz, M.; Katz, Nadav; Lucero, Erik; Neeley, M.; O’Connell, A. D.; Wang, H.; Cleland, A. N.; Martinis, John M.

doi:10.1103/physrevlett.99.187006

Cited by 202 publications

(252 citation statements)

References 18 publications

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“…The search for longer coherence times of superconducting qubits brought the study of finite-frequency electromagnetic properties of mesoscopic superconductors to the forefront of experimental research [1][2][3][4][5][6] . The majority of experiments until recently was performed on structures using Josephson junctions as "weak" superconductors, and substantial progress in recognizing the coherencelimiting mechanisms was achieved.…”

Section: Pacs Numbersmentioning

confidence: 99%

Frequency-dependent admittance of a short superconducting weak link

2013

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We consider the linear and non-linear electromagnetic responses of a nanowire connecting two bulk superconductors. Andreev states appearing at a finite phase bias substantially affect the finite-frequency admittance of such a wire junction. Electron transitions involving Andreev levels are easily saturated, leading to the nonlinear effects in photon absorption for the sub-gap photon energies. We evaluate the complex admittance analytically at arbitrary frequency and arbitrary, possibly non-equilibrium, occupation of Andreev levels. Special care is given to the limits of a single-channel contact and a disordered metallic weak link. We also evaluate the quasi-static fluctuations of admittance induced by fluctuations of the occupation factors of Andreev levels. In view of possible qubit applications, we compare properties of a weak link with those of a tunnel Josephson junction. Compared to the latter, a weak link has smaller low-frequency dissipation. However, because of the deeper Andreev levels, the low-temperature quasi-static fluctuations of the inductance of a weak link are exponentially larger than of a tunnel junction. These fluctuations limit the applicability of nanowire junctions in superconducting qubits

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Section: Pacs Numbersmentioning

confidence: 99%

Frequency-dependent admittance of a short superconducting weak link

2013

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“…1 In the case of qubits, this magnetic flux noise places fundamental limits on the performance and scalability of such architectures. Low frequency flux noise is widely thought to be due to fluctuations of magnetic impurities local to the superconductor wiring [2][3][4] but the identity of these impurities and the physical mechanism producing the observed fluctuations is not known. Understanding the fundamental origin of flux noise is important not only to aid in its reduction in superconducting devices, but also may provide insight into the behavior of disordered ensembles of spins at low temperature.…”

Section: Introductionmentioning

confidence: 99%

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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“…Their noise is known to be due to local fluctuators [6][7][8][9] and the spectrum exhibits a 1/f α powerlaw dependence from hertz to tens of megahertz [10][11][12][13][14] . Its dependence on the device geometry 15,16 merits further study.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopy of low-frequency noise and its temperature dependence in a superconducting qubit

et al. 2012

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We report a direct measurement of the low-frequency noise spectrum in a superconducting flux qubit. Our method uses the noise sensitivity of a free-induction Ramsey interference experiment, comprising free evolution in the presence of noise for a fixed period of time followed by single-shot qubit-state measurement. Repeating this procedure enables Fourier-transform noise spectroscopy with access to frequencies up to the achievable repetition rate, a regime relevant to dephasing in ensemble-averaged time-domain measurements such as Ramsey interferometry. Rotating the qubit's quantization axis allows us to measure two types of noise: effective flux noise and effective criticalcurrent or charge noise. For both noise sources, we observe that the very same 1/f -type power laws measured at considerably higher frequencies (0.2 − 20 MHz) are consistent with the noise in the 0.01 − 100-Hz range measured here. We find no evidence of temperature dependence of the noises over 65 − 200 mK, and also no evidence of time-domain correlations between the two noises. These methods and results are pertinent to the dephasing of all superconducting qubits.

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1/fFlux Noise in Josephson Phase Qubits

Cited by 202 publications

References 18 publications

Frequency-dependent admittance of a short superconducting weak link

Frequency-dependent admittance of a short superconducting weak link

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

Spectroscopy of low-frequency noise and its temperature dependence in a superconducting qubit

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