Hybrid quantum electronics with trapped ions

Quantum information processing promises to solve problems that are intractable by todays computers. Despite impressive experimental progress towards building such a device, the realization of a large-scale quantum information processor seems in the far future. Currently, multiple systems are investigated to form the basis of a future quantum information device. Naturally, each physical system has its own strengths and weaknesses and thus it seems beneficial to combine multiple systems. In this proposal, we aim to combine two promising candidates for building a quantum information processor: superconducting electronic quantum devices and atomic systems. In particular, we propose to realize a quantum hybrid device that couples trapped ions and solid state qubits based on Josephson junctions. A combination of these systems seems promising as trapped ions feature long coherence times of over a second whereas superconducting electronics allow for rapid and high quality quantum operations in less than one microsecond. As a first step towards this goal we will couple the ions quantum mechanical motion to a superconducting resonator. The proposed coupling mechanism is based on the fact that the ions motion in the trap corresponds to an alternating current that drives the superconducting resonator. The two main obstacles for realizing such a hybrid device are: Impedance mismatch, as the ions motion corresponds to an impedance that is several orders of magnitude higher than the impedance of common superconducting devices. Frequency mismatch, as high quality superconducting quantum devices operate in the Gigahertz regime but the ions motion is in the order of a few Megahertz. Within this project we will perform two experiments, where the first aims to solve the impedance mismatch and the second addresses the frequency mismatch. The first experiment will directly couple the resonator and the ions motion at a frequency of a few Megahertz. We expect this regime to be in the strong coupling regime, as the projected coupling between the two systems dominates the coupling to the classical environment. This is an ongoing experiment at the host institute. The second experiment aims to bridge the frequency gap between state-of-the-art superconducting electronics and the ions motion. There, we use a novel parametric process to upconvert the ions motion frequency by at least one order of magnitude. The proposed coupling mechanism has the advantage that it converts the signal before it enters any solid state device, avoiding the excessive low frequency noise present in these devices. In conclusion, we have proposed two distinct experiments to couple a single atomic ion with superconducting electronic devices. These experiments are interesting from a technological as well as from a fundamental physics point of view, as they combine the fields of atomic physics, quantum optics, solid state physics and nanoscience.

Quantum computers promise to solve problems that are intractable by todays computers. Despite impressive experimental progress towards building such a device, the realization of a large-scale quantum information processor seems in the far future. Currently, multiple systems are investigated to form the basis of a future quantum information device. Naturally, each physical system has its own strengths and weaknesses and thus it seems beneficial to combine multiple systems. In this project we investigated an interface for combining two promising candidates for building a quantum information processor: superconducting electronic quantum devices and atomic systems. Quantum information processors based on superconductors allow for fast and precise manipulation of the information whereas atomic systems are ideally suited as quantum memories. Within this project we could show that it is possible to transfer energy from a superconducting circuit to a single trapped atomic ion, which is a crucial prerequisite for such an interface.