Suppression of low-frequency charge noise in superconducting resonators by surface spin desorption

Abstract

Noise and decoherence due to spurious two-level systems located at material interfaces are long-standing issues for solid-state quantum devices. Efforts to mitigate the effects of two-level systems have been hampered by a lack of knowledge about their chemical and physical nature. Here, by combining dielectric loss, frequency noise and on-chip electron spin resonance measurements in superconducting resonators, we demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the charge-induced frequency noise in the resonators. These measurements provide experimental evidence that simultaneously reveals the chemical signatures of adsorbed magnetic moments and highlights their role in generating charge noise in solid-state quantum devices.

Superconductivity Behavior in Epitaxial TiN Films Points to Surface Magnetic Disorder

“…While different values of N b can account for a growth related variation between the sets, the same value of N s indicates that the observed drop of T c at decreasing d is an important systematic effect in thin epitaxial TiN films. The values of N s provide us with an estimate of the surface density of magnetic defects that is as small as a −2 N s = 10 12 cm −2 , at least an order of magnitude smaller in comparison with a typical density of the surface magnetic moments (∼ 5 × 10 13 cm −2 ), reported for Al, Nb and NbN superconductors [24,[55][56][57][58]. Note, however, that relevant for the T c reduction are only those magnetic scatterers that strongly couple to the conduction electrons.…”

Improving the Time Stability of Superconducting Planar Resonators

“…The most promising result of our work is the approximately tenfold reduction in the fractional-frequency flicker noise level between the Unprocessed and RCA Table II are obtained with 〈 〉 10, whereas in the work of Ref. [17] with 〈 〉 2.…”

“…In the work of Ref. [17], similar findings are explained within the framework of the generalized tunneling model (GTM), which is an extension of the standard tunnelling model (STM). The STM was developed to describe the effect of an ensemble of TLS defects in glasses and amorphous dielectric materials [23][24][25].…”

On-chip Thermometry for Microwave Optomechanics Implemented in a Nuclear Demagnetization Cryostat

“…Noting furthermore than with an in-cavity pumping, it disappears when the beam temperature exceeds 100 mK, we conclude that it should even be within the mechanical element. But the mechanism remains mysterious: citing only documented effects in other areas of research, is it linked to vortex motion in the superconductor [46], trapped charges [47], adsorbed molecules [48] or to atomic-size Two-Level-Systems in dielectrics (beyond the standard friction model) [49]?…”

“…It is thus natural to consider strongly coupled individual TLSs as the most probable source of our problems. Besides, while the actual nature of these microscopic defects remains elusive in most systems, they could be generated in many ways beyond the standard atomic configuration argument [54]; an electron tunneling between nearby traps would be a TLS strongly coupled to its electromagnetic environment, among other possibilities [48]. For Al-based NEMS, these would create (only a few) defects present in (or on) the Al layer; they should carry a dipole moment, which couples them to the microwave drive as well as to the electric field generated by the applied DC voltage.…”