1/ω electric-field noise in surface ion traps from correlated adsorbate dynamics

Abstract

Ion traps are promising architectures for implementing quantum computers, but they suffer from excessive "anomalous" ion motional heating that limit their overall coherence and practicality for scalable quantum computing. The exact microscopic origins of anomalous heating remain an open question, but experiments point to adsorbates on trap electrodes as one likely source. Many different models of anomalous heating have been proposed, but these models have yet to pinpoint the atomistic origin of the experimentally-observed 1/ω electric field noise scaling seen in ion traps at frequencies between 0.1-10 MHz. In this work, we show that a model based on previously-proposed surface-induced dipole fluctuations on adsorbates, but which also incorporates interparticle interaction dynamics through molecular dynamics simulations of up to multiple monolayers of adsorbates, gives rise to 1/ω frequency scaling at the MHz frequencies typically employed in ion traps. These results demonstrate that moderate-to-high densities of adsorbates can give rise to a set of activated motions that produce the 1/ω noise observed in ion traps and that collective adsorbate motions produce the observed noise spectra that a non-interacting model does not capture.

Surface-induced decoherence and heating of charged particles

“…The chosen framework facilitates a pragmatic description of surface-induced decoherence and heating in terms of macroscopic dielectric response functions. The latter are accessible both by in situ and ex situ measurements as well as by microscopic ab-initio calculations [97,98] and molecular-dynamics simulations [99]. By disentangling the effects of the surface geometry from the influence of the surface material, the derived mas-Figure 1.…”

“…( 60) can be enhanced by broad low-frequency contributions to the spectrum, each contributing with relative strength f n γ n /ω 2 n . Such weak and broad absorption bands could for instance be due to weakly bound surface adsorbates [66,99].…”

“…This encompasses accounting for the role of microscopic processes as sources and as mediators of electromagnetic noise. Ab-initio calculations [97,98] and molecular-dynamics simulations [99] link microscopic models to the macroscopic dielectric response, which in turn serves as one input for the presented toolbox and can thus be tested experimentally.…”

Surface science motivated by heating of trapped ions from the quantum ground state

“…The frequency dependence of the heating rates for a given coverage follows a power-law relation over the range of accessible frequencies for this trap. The variation in the power-law exponent α indicates that there may be a single [ 28 ] or even multiple mechanisms [ 31 ] arising from surface treatments or a change in coverage. Heating rates also are shown to have anisotropic values for the two orthogonal motional modes parallel to the surface of the trap electrodes.…”