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

TL;DR

This paper explores how longitudinal couplings in superconducting qubits enable efficient generation of nonclassical photon states, surpassing traditional methods that rely solely on transverse couplings.

Contribution

It introduces a novel approach leveraging longitudinal couplings and classical fields to generate arbitrary superpositions of Fock states in microwave cavities.

Findings

Classical fields induce controllable multiphoton transitions in superconducting qubits.

Efficient generation of arbitrary superpositions of Fock states is demonstrated.

The method shows potential for experimental realization with current superconducting qubit technologies.

Abstract

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. We show that arbitrary superpositions of Fock states can be more efficiently generated using these controllable multiphoton transitions, in contrast to the single-photon resonant transition when there is only a SQ-field transverse coupling. The experimental feasibility for different SQs is also discussed.