Contribution of dielectrics to frequency and noise of NbTiN superconducting resonators

Barends, R.; Hortensius, H. L.; Zijlstra, T.; Baselmans, J. J. A.; Yates, S. J. C.; Gao, J. R.; Klapwijk, T. M.

doi:10.1063/1.2937837

Cited by 103 publications

(112 citation statements)

References 21 publications

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“…The noise level is also found to increase with increasing loss tangent, consistent with noise increasing with increasing density of TLFs [4] [22]. At low temperatures there exists a power dependence of the noise which could scale similar to the P −1/2 int dependence suggested by Gao et al [23] however more measurements are required to verify the exact power dependence.…”

Section: (See Supplemental Materials At [Url] For [Spectral Analysis])supporting

confidence: 57%

Slow noise processes in superconducting resonators

et al. 2013

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Slow noise processes, with characteristic timescales ∼1s, have been studied in planar superconducting resonators. A frequency locked loop is employed to track deviations of the resonator centre frequency with high precision and bandwidth. Comparative measurements are made in varying microwave drive, temperature and between bare resonators and those with an additional dielectric layer. All resonators are found to exhibit flicker frequency noise which increases with decreasing microwave drive. We also show that an increase in temperature results in a saturation of flicker noise in resonators with an additional dielectric layer, while bare resonators stop exhibiting flicker noise instead showing a random frequency walk process.Slow fluctuations in charge sensitive devices have been frequently examined over the past few decades [1]. Recently, their effects were indirectly observed in superconducting qubits [2] with supporting theoretical work [3] linking them to the presence of two level fluctuators (TLFs) [4]. We present measurements directly probing these slow noise processes in superconducting resonators using a high bandwidth feedback technique with Hz level resolution [5]. Feedback maintains a lock to the resonator centre frequency indefinitely, providing a direct measure of the nature of slow fluctuations and their behavior in varying temperature, microwave drive and TLF density. Theoretical work [3] suggests that 'slow' fluctuators can have a profound -but indirect-effect on the noise and losses in superconducting devices operating at microwave frequencies such as qubits. In simplified terms the model considers two distinct ensembles of TLFs: a coherent population that couples directly to the device, and a 'slow' population which perturbs the coherent TLFs, by changing the tunnel splitting. Hence, whereas the coherent processes between the two energy levels are expected to have short time constants, they are in turn effectively being modulated by processes that can have time constants of the order of seconds or even hours.Motivated by QIP applications, recent studies on superconducting resonators have focused heavily on sources of dissipation. Measurements have evaluated the effects of magnetic fields[6] and vortex motion [7]. The remaining dissipation channel is usually attributed to the presence of TLFs. The exact nature of TLFs remains contentious, but a variety of experiments have studied their effects [8][9][10][11][12] and recent models evaluated the contributions of TLFs in varying locations [13].In this letter we study slow noise processes in low loss niobium (Nb) on sapphire resonators [11]. Resonators are by their very nature sensitive probes: any change in the environment will produce a change in the centre frequency ν 0 of the resonator; making them ideal devices for studying noise. However, measuring this noise can be difficult due to the extrinsic low frequency noise present in equipment such as amplifiers and mixers [14]. Here we overcome this problem by using a high-bandwidth measurement metho...

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Section: (See Supplemental Materials At [Url] For [Spectral Analysis])supporting

confidence: 57%

Slow noise processes in superconducting resonators

et al. 2013

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“…NbTiN has a minimal dielectric layer compared to Nb, Al and Ta. 8 We find that in the single photon regime the quality factor of NbTiN resonators is so high that the loss is largely due to the exposed substrate. In contrast, for Ta resonators the quality factor is limited by the metal surface.…”

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confidence: 96%

Minimal resonator loss for circuit quantum electrodynamics

Barends

Vercruyssen

Endo

et al. 2010

Applied Physics Letters

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109

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“…A key parameter limiting the performance is the energy relaxation time T 1 , while dephasing is relatively unimportant [7]. Resonator performance has typically been determined through classical measurements of the quality factor, and much work has yet to be done to understand the physics of the loss mechanisms and to optimize resonator designs for best performance [8,9,10,11,12].Here we show how several previously untested loss mechanisms can be eliminated or optimized to reach a measured quality factor Q m in the 200,000 to 400,000 range at low power, while the intrinsic quality factor Q i is even higher after subtraction of the coupling capacitor limited Q c . We provide detailed evidence that surface loss from two-level state (TLS) defects is an important loss mechanism.…”

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confidence: 99%

Improving the coherence time of superconducting coplanar resonators

Wang

Hofheinz

Wenner

et al. 2009

Applied Physics Letters

160

166

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The quality factor and energy decay time of superconducting resonators have been measured as a function of material, geometry, and magnetic field. Once the dissipation of trapped magnetic vortices is minimized, we identify surface two-level states (TLS) as an important decay mechanism. A wide gap between the center conductor and the ground plane, as well as use of the superconductor Re instead of Al, are shown to decrease loss. We also demonstrate that classical measurements of resonator quality factor at low excitation power are consistent with single-photon decay time measured using qubit-resonator swap experiments.Superconducting coplanar resonators have many important applications such as photon detection [1] and quantum computation [2,3], and recently have been used to host arbitrary photon states generated by coupling to qubits [4,5,6]. A key parameter limiting the performance is the energy relaxation time T 1 , while dephasing is relatively unimportant [7]. Resonator performance has typically been determined through classical measurements of the quality factor, and much work has yet to be done to understand the physics of the loss mechanisms and to optimize resonator designs for best performance [8,9,10,11,12].Here we show how several previously untested loss mechanisms can be eliminated or optimized to reach a measured quality factor Q m in the 200,000 to 400,000 range at low power, while the intrinsic quality factor Q i is even higher after subtraction of the coupling capacitor limited Q c . We provide detailed evidence that surface loss from two-level state (TLS) defects is an important loss mechanism. Finally, we show how relatively simple quality factor measurements, when taken at low power, can be used to predict the energy decay time of resonators at the single photon level.For this work, we measured various half-wavelength (λ/2) and quarter-wavelength (λ/4) coplanar resonators, as described in Fig. 1 and Table I. Aluminum (Al) films were sputter deposited and etched with a Cl 2 /BCl 3 -based reactive ion etch (RIE), whereas Rhenium (Re) was electron-beam evaporated in a molecular beam epitaxy system using a substrate temperature of 850 • C and etched with SF 6 /O 2 -based RIE. The films were fabricated as part of a multilayer process to enable testing with qubits. Q m of the resonators was determined in an adiabatic demagnetization refrigerator using standard two-port transmission measurements with a vector network analyzer. Q c 's estimated from the |S 21 | calibration were ∼400,000 (∼1,000,000) for λ/2 (λ/4) resonators but were not subtracted from Q m .For all the resonators we observed an increase in Q m as the measurement power increased and temperature T decreased. The T dependence is shown in Fig. 2 power. To avoid complications due to different geometries, we base most of the discussion on λ/4 resonators as they share a similar shape. The decrease in Q m with increasing temperature is consistent with quasiparticle dissipation. In Fig. 2(b), the fractional change in the resonance frequency ∆...

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Contribution of dielectrics to frequency and noise of NbTiN superconducting resonators

Cited by 103 publications

References 21 publications

Slow noise processes in superconducting resonators

Slow noise processes in superconducting resonators

Minimal resonator loss for circuit quantum electrodynamics

Improving the coherence time of superconducting coplanar resonators

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