Abstract
We report heating rate measurements in a microfabricated gold-on-sapphire surface electrode ion trap with a trapping height of approximately 240 μm. Using the Doppler recooling method, we characterize the trap heating rates over an extended region of the trap. The noise spectral density of the trap falls in the range of noise spectra reported in ion traps at room temperature. We find that during the first months of operation, the heating rates increase by approximately one order of magnitude. The increase in heating rates is largest in the ion-loading region of the trap, providing a strong hint that surface contamination plays a major role for excessive heating rates. We discuss data found in the literature and the possible relation of anomalous heating to sources of noise and dissipation in other systems, namely impurity atoms adsorbed onto metal surfaces and amorphous dielectrics.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. An environment free from electric field noise is important in many fields of science. For example, work in the fields of nanomechanics, nanoelectronics, superconducting quantum electronics, ion trap quantum computing and measurement of weak forces is impeded by excessive electric field noise originating from nearby surfaces. Single trapped ions are extremely sensitive sensors for this type of noise, and experiments with ions trapped near metallic surfaces reveal noise several orders of magnitude stronger than simple estimates based on Johnson noise suggest.
Main results. To date, not much is known about the origin of this noise. We use a single trapped ion to map the electric field noise above a metal surface and find that the noise depends on position and increases with time. We conjecture that the noise stems from a locally contaminated metal surface. We also present a model for the electric field noise measured in ion traps. In our model the noise originates from fluctuating electrical dipoles that can form on metal surfaces even in ultrahigh vacuum conditions. Similar mechanisms are believed to contribute to noise in superconducting electronics and dissipation in non-contact friction measurements with metallized atomic force microscopy tips, suggesting a possible common cause across the various fields encountering electric field noise.
Wider implications. This result also suggests that surface cleaning methods, widely used in the surface science community, could provide a drastic reduction in electric field noise in ion traps, a long-standing goal in the ion trap community.
Figure. Spectral density of electric field noise measured using a single ion above a gold surface, as a function of position along a line. A maximum is seen around a region of possibly high surface contamination.