We propose a scheme to couple short single photon pulses to superconducting qubits. An optical photon is first absorbed into an inhomogeneously broadened rare-earth doped crystal using controlled reversible inhomogeneous broadening. The optical excitation is then mapped into a spin state using a series of π pulses and subsequently transferred to a superconducting qubit via a microwave cavity. To overcome the intrinsic and engineered inhomogeneous broadening of the optical and spin transitions in rare-earth doped crystals, we make use of a special transfer protocol using staggered π pulses. We predict total transfer efficiencies on the order of 90%.

A protocol is discussed which allows one to realize a transducer for single photons between the optical and the microwave frequency range. The transducer is a spin ensemble, where the individual emitters possess both an optical and a magnetic-dipole transition. Reversible frequency conversion is realized by combining optical photon storage, by means of EIT, with the controlled switching of the coupling between the magnetic-dipole transition and a superconducting qubit, which is realized by means of a microwave cavity. The efficiency is quantified by the global fidelity for transferring coherently a qubit excitation between a single optical photon and the superconducting qubit. We test various strategies and show that the total efficiency is essentially limited by the optical quantum memory: It can exceed 80% for ensembles of NV centers and approaches 99% for cold atomic ensembles, assuming state-of-the-art experimental parameters. This protocol allows one to bridge the gap between the optical and the microwave regime so to efficiently combine superconducting and optical components in quantum networks

Dense and uniform particle films are deposited using a robust version of the convective particle assembly process. We analyze how the shape of the gas-liquid interface and the three-phase contact line govern the stability of convective deposition and, thus, the achievable quality of films. Interference microscopy indicates that a highly curved meniscus cannot compensate for the ubiquitous perturbation during deposition. A moderately curved meniscus provides flexibility to compensate and localize perturbation and enables reliable homogeneous deposition. We analyze which setup geometry and meniscus velocity yield appropriate meniscus shapes. The quality of the resulting films is analyzed and compared to the deposition conditions. Uniform films over areas beyond the centimeter range are accessible using the optimized process, which is suitable for functional particle coatings and templates for microstructured materials.

The following figures are frames taken from video scans that we performed for quality analysis. They show the quality of the film at positions where 2.5 cm of film had been deposited.

Alkylthiol-coated gold nanoparticles spontaneously segregate from dispersion in toluene to the toluene-vapor interface. We show that surface tension drops during segregation with a rate that depends on particle concentration. Mono- and multilayers of particles form depending on particle concentration, time, and temperature. X-ray reflectometry indicates fast monolayer formation and slow multilayer formation. A model that combines diffusion-limited segregation driven by surface energy and heterogeneous agglomeration driven by dispersive van der Waals particle interactions is proposed to describe film formation.