Experimental system design for the integration of trapped-ion and superconducting qubit systems
De Motte, Anton Grounds, Marian Rehak, A. Blanco, Bjoern Lekitsch, Gouri Shankar Giri, P. Neilinger, G. Oelsner, Evgeni V. Il’ichev, M. Grajcar, W. K. Hensinger
We present a design for the experimental integration of ion trapping and superconducting qubit systems as a step towards the realization of a quantum hybrid system. The scheme addresses two key difficulties in realizing such a system: a combined microfabricated ion trap and superconducting qubit architecture, and the experimental infrastructure to facilitate both technologies. Developing upon work by Kielpinski et al. (Phys Rev Lett 108(13):130504, 2012. doi: 10.1103/PhysRevLett.108.130504 ), we describe the design, simulation and fabrication process for a microfabricated ion trap capable of coupling an ion to a superconducting microwave LC circuit with a coupling strength in the tens of kHz. We also describe existing difficulties in combining the experimental infrastructure of an ion trapping set-up into a dilution refrigerator with superconducting qubits and present solutions that can be immediately implemented using current technology.
We present a design for the experimental integration of ion trapping and superconducting qubit systems as a step towards the realization of a quantum hybrid system. The scheme addresses two key difficulties in realizing such a system: a combined microfabricated ion trap and superconducting qubit architecture, and the experimental infrastructure to facilitate both technologies. Developing upon work by Kielpinski et al. (Phys Rev Lett 108(13):130504, 2012. doi: 10.1103/PhysRevLett.108.130504 ), we describe the design, simulation and fabrication process for a microfabricated ion trap capable of coupling an ion to a superconducting microwave LC circuit with a coupling strength in the tens of kHz. We also describe existing difficulties in combining the experimental infrastructure of an ion trapping set-up into a dilution refrigerator with superconducting qubits and present solutions that can be immediately implemented using current technology.
We present a design for the experimental integration of ion trapping and superconducting qubit systems as a step towards the realization of a quantum hybrid system. The scheme addresses two key difficulties in realizing such a system; a combined microfabricated ion trap and superconducting qubit architecture, and the experimental infrastructure to facilitate both technologies. Developing upon work by Kielpinski et al. [1] we describe the design, simulation and fabrication process for a microfabricated ion trap capable of coupling an ion to a superconducting microwave LC circuit with a coupling strength in the tens of kHz. We also describe existing difficulties in combining the experimental infrastructure of an ion trapping setup into a dilution fridge with superconducting qubits and present solutions that can be immediately implemented using current technology.
Quantum technology has made great strides in the last two decades with trapped ions demonstrating all the necessary building blocks for a quantum computer. While these proof of principle experiments have been demonstrated, it still remains a challenging task to scale these experiments down to smaller systems. In this thesis I describe the development of technology towards scalable cryogenic ion trapping and quantum hybrid systems. I first discuss the fundamentals of ion trapping along with the demonstration of ion trapping on a novel surface electrode ion trap with a ring shaped architecture. I then present the development of a cryogenic vacuum system for ion trapping at ~4 K, which utilizes a closed cycle Gifford McMahon cryocooler with a helium gas buffered ultra-low vibration interface to mechanically decouple a ultra-high vacuum system. Ancillary technologies are also presented, including a novel in-vacuum superconducting rf resonator, low power dissipation ceramic based atomic source oven and an adaptable in-vacuum permanent magnet system for long-wavelength based quantum logic. The design and fabrication of microfabricated surface ion traps toward quantum hybrid technologies are then presented. A superconducting ion trap with an integrated high quality factor microwave cavity and vertical ion shuttling capabilities is described. The experimental demonstration of the cavity is also presented with quality factors of Q6~6000 and Q~15000 for superconducting niobium nitride and gold based cavities respectively, which are the highest demonstrated for microwave cavities integrated within ion trapping electrode architectures. An ion trap with a multipole electrode geometry is then presented, which is capable of trapping a large number of ions simultaneously. The homogeneity of five individual linear trapping regions are optimized and the design for the principle axis rotation of each linear region is presented. An overview of microfabrication techniques used for fabricating surface electrode ion traps is then presented. This includes the detailed microfabrication procedure for ion traps designed within this thesis. A scheme for the integration of ion trapping and superconducting qubit systems as a step towards the realization of a quantum hybrid system is then presented. This scheme addresses two key diffculties in realizing such a system; a combined microfabricated ion trap and superconducting qubit architecture, and the experimental infrastructure to facilitate both technologies. Solutions that can be immediately implemented using current technology are presented. Finally, as a step towards scalability and hybrid quantum systems, the interaction between a single ion and a microwaves field produced from an on chip microwave cavity is explored. The interaction is described for the high-Q microwave cavity designed in this thesis and a 171Yb+ion. A description of the observable transmission from the cavity is described and it is shown that the presence of a single ion can indeed be observed in the emission spectrum of high-Q microwave cavity even in the weak coupling regime.
Quantum computing is rapidly evolving from theoretical frameworks to functional hardware, with physical qubits now being realized across multiple experimental platforms. Precision nanofabrication has enabled the development of low-loss, high-coherence quantum devices. Among the various approaches, superconducting circuits and trapped-ion systems have emerged as the most advanced and experimentally successful platforms for realizing controllable and scalable qubits. This review presents an overview of nanoscale fabrication techniques employed in these two architectures. We first outline the operating principles that define qubit behavior, followed by a discussion of representative device designs and fabrication workflows. In superconducting circuits, we examine processes such as thin-film deposition, lithographic patterning, and Josephson-junction fabrication that determine key parameters including qubit frequency, anharmonicity, and coherence. For trapped-ion systems, we describe the transition from bulk electrode assemblies to microfabricated surface traps produced using photolithography, metal deposition, and dielectric layering, where electrode geometry and surface treatment directly influence ion confinement and motional heating. We further discuss fabrication-related challenges, including dielectric loss, surface contamination, and material defects that limit coherence and reproducibility, along with emerging mitigation strategies such as advanced cleaning, low-loss materials, and improved surface engineering. By drawing parallels between these two leading platforms, this review highlights that continued progress in nanofabrication remains central to realizing scalable, high-fidelity quantum processors.
Over the past 15 years ion traps have demonstrated all the building blocks required of a quantum computer. Despite this success, trapping ions remains a challenging task, with the requirement for extensive laser systems and vacuum systems to perform operations on only a handful of qubits. To scale these proof of principle experiments into something that can outperform a classical computer requires an advancement in the trap technologies that will allow multiple trapping zones, junctions and utilize scalable fabrication technologies. I will discuss the construction of an ion trapping experiment, focussing on my work towards the laser stabilization and ion trap design but also covering the experimental setup as a whole. The vacuum system that I designed allows the mounting and testing of a variety of ion trap chips, with versatile optical access and a fast turn around time. I will also present the design and fabrication of a microfabricated Y junction and a 2- dimensional ion trap lattice. I achieve a suppression of barrier height and small variation of secular frequency through the Y junction, aiding to the junctions applicability to adiabatic shuttling operations. I also report the design and fabrication of a 2-D ion trap lattice. Such structures have been proposed as a means to implement quantum simulators and to my knowledge is the first microfabricated lattice trap. Electrical testing of the trap structures was undertaken to investigate the breakdown voltage of microfabricated structures with both static and radio frequency voltages. The results from these tests negate the concern over reduced rf voltage breakdown and in fact demonstrates breakdown voltages significantly above that typically required for ion trapping. This may allow ion traps to be designed to operate with higher voltages and greater ion-electrode separations, reducing anomalous heating. Lastly I present my work towards the implementation of magnetic fields gradients and microwaves on chip. This may allow coupling of the ions internal state to its motion using microwaves, thus reducing the requirements for the use of laser systems.
Microfabricated ion traps are an important tool in the development of scalable quantum systems. Tremendous advancements towards an ion quantum computer were made in the past decade and most requirements for a quantum computer have been fulfilled in individual experiments. Incorporating all essential capabilities in a fully scalable system will require the further advancement of established quantum information technologies and development of new trap fabrication techniques. In my thesis I will discuss the theoretical background and experimental setup required for the operation of ion traps. Measurement of the important ion trap heating rate was performed in the setup and I will discuss the results in more detail. I will give a review of microfabrication processes used for the fabrication of traps, outlining advantages, disadvantages and issues inherent to the processes. Following the review I will present my work on a concept for a scalable ion trap quantum system based on microwave quantum gates and shuttling through X-junctions. Many of the required building blocks, including ion trap structures with current-carrying wires intended to create strong magnetic field gradients for microwave gates were investigated further. A novel fabrication process was developed to combine current-carrying wires with advanced multilayered ion trap structures. Several trap designs intended for proof of principle experiments of high fidelity microwave gates, advanced detection techniques and shuttling between electrically disconnected ion traps will be presented. Also the electrode geometry of an optimized X-junction design with strongly suppressed rf barrier height will be presented. Further, I developed several modifications for the experimental setup to extend the existing capabilities. A plasma source capable of performing in-situ cleans of the trap electrode surfaces, which has been demonstrated to dramatically reduce the heating rate in ion traps, was incorporated. I will also present a vacuum system modification designed to cool ion traps with current-carrying wires and transport the generated heat out of the vacuum system. In addition a novel low-noise, high-speed, multichannel voltage control system was developed by me. The device can be used in future experiments to precisely shuttle ions from one trapping zone to another and also to shuttle ions through ion trap junctions. Lastly I will outline the process optimization and microfabrication of my ion trap designs. A novel fabrication process which makes use of the extremely high thermal conductivity of diamond substrates and combines it with thick copper tracks embedded in the substrate was developed. Large currents will be passed through the wires creating a strong and controllable magnetic field gradient. Ion trap designs with isolated electrodes connected via buried wires can be placed on top of the current-carrying wires, allowing the most advanced electrode designs to be fabricated with current-carrying wires.
In this dissertation, we present work on a quantum hybrid device comprising of a trapped calcium atom and a superconducting LC resonator. This hybrid device is a first step towards building a hybrid quantum computer that can take advantage of the different properties of atomic and superconducting quantum systems and combine the best characteristics of both. We model a trapped ion as an LC circuit and calculate its coupling to a mode of an LC resonator. Further, we optimize the trap geometry and placement of coupling electrodes to increase the coupling. We also outline the manufacturing process and simulation of the trapping potentials for the surface traps used in this work. Finally, we report on initial experiments coupling a trapped ion to a resonant mode of the LC resonator, increasing the heating rate to 220 phonons/ms on resonance versus 0.5 phonons/ms without additional heating from the resonator. The ratio of the heating rates for the two secular frequencies of the ion confrm our simulated coupling rates.