Saturation of the dielectric absorption of vitreous silica at low temperatures

Schickfus, M. von; Hunklinger, Siegfried

doi:10.1016/0375-9601(77)90558-8

Cited by 88 publications

(81 citation statements)

References 18 publications

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“…At temperatures much below the superconducting critical temperature, T c , these mechanisms saturate. When lowering the temperature beyond this saturation a further change in both Q and center frequency is observed, which is well described in the theory of TLFs [16] [17], by modeling a single TLF as a dipole that can shift states in an asymmetric well by thermally activated tunneling or absorption of resonant photons. The former effect leads to a change in the center frequency while the latter manifests as a power dependent Q.…”

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confidence: 65%

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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confidence: 65%

Slow noise processes in superconducting resonators

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“…This effect with TLSs was fi rst observed by Schickfus and Hunklinger, who used a superconducting cavity resonator to measure the dielectric absorption of vitreous silica. 50 More recently, in the context of studying loss mechanisms relevant to superconducting qubits, Martinis et al used a lumped-element LC resonator to measure the loss tangent of chemical vapor-deposited SiO 2 and SiN x dielectrics at low temperature and variable power. 43 Both showed a decrease in tan δ with increasing power, but over the entire range studied, the SiN x loss was about 30 times lower (see Figure 5 ).…”

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confidence: 99%

Materials in superconducting quantum bits

2013

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“…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 deep reactive ion etch (DRIE) using the BOSCH process that does not require any additional steps to mask or protect the devices 16,20,21 . We begin with high resistivity (100) silicon wafers (ρ > 10 4 Ω·cm) and fabricate aluminum 3D transmon qubits using the standard Dolan bridge doubleangle deposition technique 22 .…”

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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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Saturation of the dielectric absorption of vitreous silica at low temperatures

Cited by 88 publications

References 18 publications

Slow noise processes in superconducting resonators

Slow noise processes in superconducting resonators

Materials in superconducting quantum bits

Suspending superconducting qubits by silicon micromachining

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