Cross Kerr Effect Induced by Coupled Josephson Qubits in Circuit Quantum Electrodynamics

TL;DR

This paper proposes a robust scheme to induce strong cross Kerr nonlinearity between two superconducting resonators using coupled Josephson charge qubits, enabling advanced quantum operations with minimal decoherence effects.

Contribution

It introduces a novel design for achieving significant cross Kerr effects via a coupled qubit system with high robustness against circuit fluctuations.

Findings

Large cross Kerr coefficient enabling quantum operations with few photons

Scheme exhibits high robustness against circuit fluctuations

Decoherence effects are minimal compared to the Kerr nonlinearity

Abstract

We propose a scheme for implementing cross Kerr nonlinearity between two superconducting transmission line resonators (TLR) via their interaction with a coupler which is constructed by two superconducting charge qubits connected to each other via a superconducting quantum interference device. When suitably driven, the coupler can induce very strong cross phase modulation (XPM) between the two TLRs due to its N-type level structure and the consequent electromagnetically induced transparency in its lowest states. The flexibility of our design can lead to various inter-TLR coupling configurations. The obtained cross Kerr coefficient is large enough to allow many important quantum operations in which only few photons are involved. We further show that this scheme is very robust against the fluctuations in solid state circuits. Our numerical calculations imply that the absorption and dispersion resulted from the decoherence of the coupler are very small compared with the strength of the proposed XPM.