Generating nonclassical photon-states via longitudinal couplings between superconducting qubits and microwave fields

Understand

Besides the conventional transverse couplings between superconducting qubits (SQs) and electromagnetic fields, there are additional longitudinal couplings when the inversion symmetry of the potential energies of the SQs is broken.

• We study nonclassical-state generation in a SQ which is driven by a classical field and coupled to a single-mode microwave field.
• We find that the classical field can induce transitions between two energy levels of the SQs, which either generate or annihilate, in a controllable way, different photon numbers of the cavity field.
• The effective Hamiltonians of these classical-field-assisted multiphoton processes of the single-mode cavity field are very similar to those for cold ions, confined to a coaxial RF-ion trap and driven by a classical field.