Multi-Species Trapped Atomic Ion Modules for Quantum Networks

Trapped atomic ions are among leading platforms in quantum information processing with their long coherence times and high fidelity quantum operations. Scaling up to larger numbers of qubits is a remaining major challenge. A network of trapped ion modules offers a promising solution by keeping a manageable number of qubits within a module while photonic interfaces connect separate modules together to increase the number of controlled memory qubits. Since the generation of entanglement between qubits in different modules is probabilistic, an excessive number of connection trials might result in decoherence on the memory qubits through absorption of stray photons. This crosstalk issue could be circumvented by introducing a different atomic species as photonic qubits. Compared to a system that only utilizes single species of atoms, there are also additional advantages in a multi-species apparatus where attractive features of each atom can be employed for certain tasks. In this thesis, I present experimental demonstrations of necessary ingredients of a multi-species module for quantum networking. In these experiments, barium ions are intended to be used as photonic communication qubits with visible photon emission lines that are more convenient for current fiber optics and detector technologies while ytterbium ions are used for storing and processing quantum information where long coherence times available in hyperfine clock states make them suitable memory qubits. The key experiments include demonstration of atom-photon entanglement using the barium qubit and utilizing the Coulomb interaction between ytterbium and barium with spin-dependent forces for transfer of information from communication to memory qubits

Coherent Error Suppression in Multi-Qubit Entangling Gates

We demonstrate a simple pulse shaping technique designed to improve the fidelity of spin-dependent force operations commonly used to implement entangling gates in trapped-ion systems. This extension of the M{\o}lmer-S{\o}rensen gate can theoretically suppress the effects of certain frequency and timing errors to any desired order and is demonstrated through Walsh modulation of a two-qubit entangling gate on trapped atomic ions. The technique is applicable to any system of qubits coupled through collective harmonic oscillator modes

Engineering of microfabricated ion traps and integration of advanced on-chip features

Atomic ions trapped in electromagnetic potentials have long been used for fundamental studies in quantum physics. Over the past two decades, trapped ions have been successfully used to implement technologies such as quantum computing, quantum simulation, atomic clocks, mass spectrometers and quantum sensors. Advanced fabrication techniques, taken from other established or emerging disciplines, are used to create new, reliable ion-trap devices aimed at large-scale integration and compatibility with commercial fabrication. This Technical Review covers the fundamentals of ion trapping before discussing the design of ion traps for the aforementioned applications. We overview the current microfabrication techniques and the various considerations behind the choice of materials and processes. Finally, we discuss current efforts to include advanced, on-chip features in next-generation ion traps