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Qubits of long coherence time and fast quantum operations are long-sought objectives toward the realization of high-fidelity quantum operations and their applications to quantum technologies. An electron levitated in a vacuum by a Paul trap is expected to be a good candidate, for its light mass and hence the high secular frequency which allows for faster gate operations than those in trapped ions. Controlling the motional state of the trapped electron is a crucial issue, for it mediates an interaction between electron spins, intrinsic qubits embedded in electrons, and its decoherence results in degraded fidelity of two-qubit gates. In addition, an efficient readout of the motional state is important, regarding the possibility of detecting spin state by using it. Despite such importance, how to achieve the motional ground state and how to efficiently detect it are not reported so far. Here we propose methods addressing these issues by utilizing hybrid quantum systems involving an electron-superconducting circuit and electron-ion coupled systems and analyze the feasibility of our schemes. In both systems, we show that ground-state cooling and single-phonon readout of the motional state of the trapped electron are possible. Our work sheds light on a way to precisely control the motional states of the trapped electrons, that provides an interesting playground for the development of quantum technologies.

Silicon photonics is a powerful platform for implementing large-scale photonic integrated circuits (PICs) because of its compatibility with mature complementary-metal-oxide-semiconductor (CMOS) technology. Exploiting silicon-based PICs for quantum photonic information processing (or the so-called silicon quantum photonics) provides a promising pathway for large-scale quantum applications. For the development of scalable silicon quantum PICs, a major challenge is integrating on-silicon quantum light sources that deterministically emit single photons. In this regard, the use of epitaxial InAs/GaAs quantum dots (QDs) is a very promising approach because of their capability of deterministic single-photon emission with high purity and indistinguishability. However, the required hybrid integration is inherently difficult and often lacks the compatibility with CMOS processes. Here, we demonstrate a QD single-photon source integrated on a glass-clad silicon photonic waveguide processed by a CMOS foundry. Hybrid integration is performed using transfer printing, which enables us to integrate heterogeneous optical components in a simple pick-and-place manner and thus assemble them after the entire CMOS process is completed. We observe single-photon emission from the integrated QD and its efficient coupling into the silicon waveguide. Our transfer-printing-based approach is fully compatible with CMOS back-end processes and thus will open the possibility for realizing large-scale quantum PICs that leverage CMOS technology.

We report a valley photonic crystal (VPhC) waveguide in a GaAs slab with InAs quantum dots (QDs) as an internal light source exploited for the experimental characterization of the waveguide. A topological interface state formed at the interface between two topologically-distinct VPhCs is used as the waveguide mode. We demonstrate robust propagation for the near-infrared light emitted from the QDs, even with the presence of sharp bends, due to the topological protection of the guided mode. Our work will be of importance for developing robust photonic integrated circuits with small footprints, as well as for exploring active semiconductor topological photonics. [ABSTRACT FROM AUTHOR]