Tobias Sägesser


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Sägesser

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Tobias

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0000-0002-6895-9096

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2020 - 20255
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Publications 1 - 5 of 5
  • A Trapped-Ion Scanning Probe
    Item type: Doctoral Thesis
    Sägesser, Tobias (2025)
    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.
  • Robust dynamical exchange cooling with trapped ions
    Item type: Journal Article
    Sägesser, Tobias; Matt, Roland; Oswald, Robin; et al. (2020)
    New Journal of Physics
    We investigate theoretically the possibility for robust and fast cooling of a trapped atomic ion by transient interaction with a pre-cooled ion. The transient coupling is achieved through dynamical control of the ions' equilibrium positions. To achieve short cooling times we make use of shortcuts to adiabaticity by applying invariant-based engineering. We design these to take account of imperfections such as stray fields, and trap frequency offsets. For settings appropriate to a currently operational trap in our laboratory, we find that robust performance could be achieved down to 6.3 motional cycles, comprising 14.2 μs for ions with a 0.44 MHz trap frequency. This is considerably faster than can be achieved using laser cooling in the weak coupling regime, which makes this an attractive scheme in the context of quantum computing.
  • Microfabricated Penning trap for quantum computation and simulation
    Item type: Conference Paper
    Hrmo, Pavel; Jain, Shreyans; Sägesser, Tobias; et al. (2022)
    2022 IEEE International Conference on Quantum Computing and Engineering (QCE)
    Trapped ion quantum information processors as well as all competing platforms are facing a challenging task to scale up their qubit registers. Trapped ion systems typically use strong radio-frequency (r.f.) fields for confinement, which present a technological challenge in delivering the required power to miniaturized surface traps with a two-dimensional geometry. Such a geometry is desired for scaling in a large information process but is fundamentally at odds with the fact that any ions straying away from one-dimensional r.f. nulls suffer excess micromotion. We instead envision a two-dimensional array of Penning traps that will operate free from the detrimental strong r.f. fields: a repeating pattern of dc electrodes on a microfabricated trap chip with static quadrupole potentials will create an axial confinement at each trap site and in combination with a strong and homogenous magnetic field generate radial confinement. Each individual trap site would then host a single ion and would be easily reconfigurable to adjust the distance to a neighboring site to allow for tunable coupling strengths. To demonstrate the feasibility of this approach, we built an experimental apparatus that houses a micro-fabricated trap capable of creating two radially separated trapping wells inside a cryogenic vacuum chamber inserted into the bore of a 3 T superconducting magnet. We report on the first successful loading of 9 Be + ions into the trap. The results highlight our ability to successfully cool the radial motion using the radial motional mode coupling technique known as axialization.
  • Penning micro-trap for quantum computing
    Item type: Journal Article
    Jain, Shreyans; Sägesser, Tobias; Hrmo, Pavel; et al. (2024)
    Nature
    Trapped ions in radio-frequency traps are among the leading approaches for realizing quantum computers, because of high-fidelity quantum gates and long coherence times1,2,3. However, the use of radio-frequencies presents several challenges to scaling, including requiring compatibility of chips with high voltages4, managing power dissipation5 and restricting transport and placement of ions6. Here we realize a micro-fabricated Penning ion trap that removes these restrictions by replacing the radio-frequency field with a 3 T magnetic field. We demonstrate full quantum control of an ion in this setting, as well as the ability to transport the ion arbitrarily in the trapping plane above the chip. This unique feature of the Penning micro-trap approach opens up a modification of the quantum charge-coupled device architecture with improved connectivity and flexibility, facilitating the realization of large-scale trapped-ion quantum computing, quantum simulation and quantum sensing.
  • Demonstration of a micro-fabricated Penning trap for quantum computing
    Item type: Conference Paper
    Sägesser, Tobias; Jain, Shreyans; Hrmo, Pavel; et al. (2023)
    2023 IEEE International Conference on Quantum Computing and Engineering (QCE)
    Trapped-ion quantum information processors are among the leading candidates to realise large-scale quantum computing. In trying to scale the number of confined ions in radio-frequency (rf) traps, several challenges arise due to the use of the rf fields. Ion placement is restricted to the vicinity of the rf null in order to minimise excess micromotion. Miniaturisation of trap geometries is desirable for increased ion density, but is at odds with the need to deliver high-voltage rf and tolerate the resulting power dissipation. We demonstrate a platform based on Penning traps, where ions are radially confined using a strong magnetic field. Static electric fields are then sufficient to provide confinement along the axis. We confine a single ⁹Be + ion in a 3 T magnetic field using a micro-fabricated trap and realise transport to arbitrary positions above the trap chip. Furthermore, we show full quantum control of the spin and motion of the trapped ion. Ground state cooling of all motional modes is achieved and we measure the rate of motional heating due to electric field noise in the absence of an rf drive, obtaining noise levels below those observed in similar rf traps. Since only static fields are required for ion confinement, we can temporarily electrically isolate the trap electrodes from technical noise using switches, further reducing the observed electric field noise.
Publications 1 - 5 of 5