Speaker
Description
For applications of ion traps in quantum computing and metrology, understanding the origins of anomalous heating and dc stray fields is highly relevant. Anomalous heating and stray fields can both be linked to effects occurring on the ion trap surface e.g., adsorbate movement, fluctuating dipoles, two level fluctuators for anomalous heating and laser-induced charging, surface contaminations for stray fields[1], [2]. Despite numerous studies on different materials no definitive conclusion on root causes could be reached, yet. Some of the most recent studies focus on analyzing the elemental composition of ion trap surfaces using techniques such as Auger electron microscopy and X-ray photoelectron spectroscopy (XPS), aiming to improve the understanding of ion trap surfaces[3], [4].
In our research, we use a Kelvin probe force microscope (KPFM) to study ion trap surfaces. Unlike XPS, KPFM does not analyze the elemental composition of the surface, but rather the electrical potential. The KPFM technique is based on atomic force microscopy; therefore, a very fine tip is used to scan the sample surface. During this scan, the topography and surface potential are mapped simultaneously. The ion trap potential can be derived from the electrical potential the tip is measuring. However, due to the tip's small diameter of approximately 10 nm, a much higher lateral resolution can be achieved than with the ion itself.
Using this technique in ambient conditions, we demonstrate that the common assumption in ion trapping, that metals have an equipotential surface, is a drastic oversimplification. For both noble and non-noble metals, we found that surface potential divergences of 50–100 mV are common for chip trap surfaces. In certain cases, potential changes up to 0.5V were found. The main reasons for these changes in potential are grain boundaries and changes in grain structure.
In addition to these changes in untreated surfaces, we demonstrated that exposing aluminum to blue laser wavelengths alters the surface potential by up to 0.45 V (Illumination settings: Wavelength:405nm; Laser Power: 100µW; Laser diameter: 10µm; Illumination time: 5s) . We demonstrated that the change in potential is locally confined and stable over several days. Experiments are currently being conducted to show the correlation between these KPFM measurements and in-situ ion trap measurements
[1] S. X. Wang et.al „Laser-induced charging of microfabricated ion traps“,
doi: 10.1063/1.3662118.
[2] M. Brownnutt et.al, „Ion-trap measurements of electric-field noise near surfaces“, doi: 10.1103/RevModPhys.87.1419.
[3] M. Berlin-Udi et al., „Changes in electric field noise due to thermal transformation of a surface ion trap“, doi: 10.1103/PhysRevB.106.035409.
[4] J. A. Sedlacek et al. „Evidence for multiple mechanisms underlying surface electric-field noise in ion traps“, doi: 10.1103/PhysRevA.98.063430.
| Academic level | PhD student |
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