A Quantum Interface to Electrons in a Vacuum

An electron detector capable of transferring the quantum state of an electron to a set of superconducting qubits is proposed. The key element of the detector, which is insensitive to the kinetic energy of the electron, is a superconducting flux qubit with a ring-shaped magnetic flux quantum. The scheme enables quantum state transfer back to an electron as well. A single such qubit will already allow for non-destructive charged particle detection, leading to a potentially useful application. Major causes of measurement errors are also examined.