A Trapped-Ion Scanning Probe
EMBARGOED UNTIL 2026-06-11
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Date
2025
Publication Type
Doctoral Thesis
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yes
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EMBARGOED UNTIL 2026-06-11
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Abstract
Trapped ions are a leading platform for quantum information processing as well as for precise
measurement of physical quantities through quantum sensing protocols. Both applications rely
on the excellent control techniques available, enabling high-fidelity operations as well as allowing
entanglement-enhanced sensing precision. One major advantage of trapped ions is their capability
to be spatially translated, allowing quantum computation with all-to-all connectivity and
quantum sensing with nanometer-scale spatial resolution across macroscopic ranges. However,
the use of radio-frequency (rf) fields for confinement limits the scalability and flexibility of
trapped-ion platforms by only allowing translation along linear paths. By operating traps with
micro-fabricated electrodes as Penning traps, ions can be controlled using only static electric and
magnetic fields, allowing confinement at arbitrary locations. This freedom of placement provides
a path to quantum computers with improved scalability based on two- or three-dimensional ion
arrays as well as towards a quantum sensing platform capable of scanning the probe ions in
3-d.
During the course of this doctoral thesis, we operated a single 9Be+ ion as such a scanning probe.
For this purpose, we built the first ever experimental apparatus consisting of a micro-fabricated
surface-electrode trap placed within a cryogenic vacuum apparatus and embedded in a 3 T magnetic
field. We probe electric and magnetic fields, both of static and time-varying nature, in 3-d
for the first time. Measuring above a 200 μm × 200 μm region of the trap surface and at ion–
surface distances between 50 μm and 450 μm, we infer the distribution of electric dipoles on the
electrode surface as well as the spatial distribution of electric-field noise in 3-d. Using the full
information provided by the latter measurement allows us to distinguish between the contributing
noise sources, including processes on the trap surface as well as external technical equipment.
For decades, uncontrolled electric fields have plagued attempts to operate ions as carriers of
quantum information in the proximity of surfaces. This work contains one of the most comprehensive
studies of such surface noise to date.
The results presented here, together with concurrent work, form the foundation of a quantum
sensing and surface science platform based on Penning micro-traps, which promises to extend
the full tool set of quantum sensing to 3-d spatial resolution. The obtained methods for controlling
the trapping potentials and 3-d translation of ions also constitute a further step towards a
quantum computing platform using Penning micro-traps.
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Examiner : Home, Jonathan
Examiner : Sawyer, Brian C.
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ETH Zurich
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03892 - Home, Jonathan / Home, Jonathan