Technologies for trapped-ion quantum information systems (1502.05739v2)

Abstract: Scaling-up from prototype systems to dense arrays of ions on chip, or vast networks of ions connected by photonic channels, will require developing entirely new technologies that combine miniaturized ion trapping systems with devices to capture, transmit and detect light, while refining how ions are confined and controlled. Building a cohesive ion system from such diverse parts involves many challenges, including navigating materials incompatibilities and undesired coupling between elements. Here, we review our recent efforts to create scalable ion systems incorporating unconventional materials such as graphene and indium tin oxide, integrating devices like optical fibers and mirrors, and exploring alternative ion loading and trapping techniques.

• The paper presents the integration of novel materials and optical components to enhance scalability and coherence in trapped-ion quantum systems.
• It demonstrates that surface phenomena, evidenced by superconducting traps and graphene coatings, critically impact motional heating and decoherence.
• Additionally, the study explores hybrid trapping methods and CMOS fabrication to pave the way for robust, scalable quantum computing architectures.

Technologies for Trapped-Ion Quantum Information Systems

Introduction

The evolution of quantum information processing (QIP) technologies based on trapped ions has necessitated the exploration of scalable systems to transition from laboratory-scale prototypes to practical architectures. This paper primarily addresses the integration of novel materials and optical components to improve ion trap systems, while maintaining coherence and scalability. The integration of optical elements not only underpins quantum manipulation and readout but also facilitates interfacing with optical networks.

Figure 1: The canonical four-rod Paul trap has been a workhorse for early demonstrations of QIP with ions.

Ion Trap Materials and Decoherence Mitigation

A major challenge in the miniaturization of ion traps is reducing electric field noise, which contributes to motional heating. Superconducting ion traps were found to exhibit unchanged heating rates across superconducting transitions, implicating surface phenomena as the primary cause. Similarly, attempts to use graphene coatings to prevent heating revealed increased rates, suggesting contamination from residual hydrocarbons as a potential cause.

Figure 2: An ion trap with superconducting electrodes, demonstrating unchanged heating rates across superconducting transitions.

Integration with Optical Components

The integration of optical fibers, transparent electrodes, and mirrors creates possibilities for scalable quantum computation while addressing constraints such as dielectric interference and alignment. Optical fibers embedded into traps allow precise light delivery, enhancing individual ion addressability. Transparent electrode traps enable photon collection through ion traps, enhancing detection efficiency.

Figure 3: A single-mode optical fiber embedded into a surface trap has been used to deliver light to a single ion, successfully addressing the qubit transition.

Ion-Photon Interaction through Optical Cavities

Optical cavities enhance ion-photon coupling, enabling collective coupling with multiple ions to reach strong coupling regimes. Applications include cavity-aided cooling, which bypasses the internal state, and Lamb-Dicke parameter engineering for rotational states in molecular ions, facilitating coherent control in ion-molecule systems.

Figure 4: A microfabricated planar trap array of ion chains coupled to an optical cavity forms a collective ion-photon interface.

Hybrid Optical and Electrostatic Traps

Optical lattice trapping offers a micromotion-free environment advantageous for trapping ions, though it introduces challenges like recoil heating and light shifts. The combination of RF Paul traps with optical lattices confines ions in deep optical potentials while mitigating RF heating, forming a base for scalable ion qubits integrated with optical systems.

Figure 5: A hybrid 1D optical lattice - RF Paul trap system has been developed.

Neutral Atom Integration for Ion Loading

Hybrid systems enabling the loading of ions from magneto-optical traps (MOTs) address challenges of trap miniaturization and ion purity. Successful demonstrations of loading from MOTs indicate improved control over isotopic purity and atom-ion interactions, which are critical for large-scale ion trapping architectures.

Figure 6: An apparatus for loading a surface-electrode ion trap by in-trap photoionization of laser-cooled atoms has been developed.

CMOS Foundry Fabrication

Fabrication of ion traps using commercial CMOS processes demonstrates potential for large-scale integration, offering the advantages of high reproducibility and enhanced functionality. Co-integration with CMOS electronics and photonics could enable sophisticated control systems for QIP.

Figure 7: A surface-electrode ion trap was fabricated entirely within a commercial CMOS foundry process.

Conclusion

This paper explores a range of technology developments to enhance the scalability and coherence of trapped-ion QIP systems. By integrating novel materials, optical components, hybrid trapping systems, and leveraging CMOS fabrication processes, the work fosters pathways towards robust, practical implementation of quantum information networks. Continued exploration into hybrid ion traps promises advancement towards scalable quantum computing.