Mobile qubits in quantum Josephson circuits

A massive mobile qubit is proposed that uses quantum-mechanical aspects of a mobile bound excitation pair consisting of a fluxon and an antifluxon, called a breather, in a long Josephson junction with small capacitance per unit length. This massive mobile qubit acts as a quantum data bus that transfers quantum information from one node to another. Moreover, it performs calculations during communication without the support of stationary qubits. In addition, the proposed qubits are elementary excitations that are regarded as macroscopic artificial two-level atoms. This means they can be introduced anytime and anywhere on demand in contrast to built-in solid-state qubits. They provide a platform for testing fundamental problems in quantum mechanics on a macroscopic scale.