A quantum interface to charged particles in a vacuum

A superconducting qubit device suitable for interacting with a flying electron has recently been proposed [H. Okamoto and Y. Nagatani, Appl. Phys. Lett. \textbf{104}, 062604 (2014)]. Either a clockwise or counter clockwise directed loop of half magnetic flux quantum encodes a qubit, which naturally interacts with any single charged particle with arbitrary kinetic energy. Here, the device's properties, sources of errors and possible applications are studied in detail. In particular, applications include detection of a charged particle without applying a force to it. Furthermore, quantum states can be transferred between an array of the proposed devices and the charged particle.