Circuit QED: Cross-Kerr-effect induced by a superconducting qutrit without classical pulses

TL;DR

This paper proposes a pulse-free method to realize cross-Kerr nonlinearity between superconducting resonators using a three-level qutrit, enabling high-fidelity quantum gates and entangled states with minimal decoherence.

Contribution

It introduces a classical-pulse-free approach for cross-Kerr interaction in circuit QED using a simplified three-level qutrit system, reducing experimental complexity and decoherence effects.

Findings

High-fidelity controlled-phase gate demonstrated in simulations

Generation of entangled coherent states feasible with current technology

Minimized coupler decoherence due to unexcited coupler during operation

Abstract

The realization of cross-Kerr nonlinearity is an important task for many applications in quantum information processing. In this work, we propose a method for realizing cross-Kerr nonlinearity interaction between two superconducting coplanar waveguide resonators coupled by a three-level superconducting flux qutrit (coupler). By employing the qutrit-resonator dispersive interaction, we derive an effective Hamiltonian involving two-photon number operators and a coupler operator. This Hamiltonian can be used to describe a cross-Kerr nonlinearity interaction between two resonators when the coupler is in the ground state. Because the coupler is unexcited during the entire process, the effect of coupler decoherence can be greatly minimized. More importantly, compared with the previous proposals, our proposal does not require classical pulses. Furthermore, due to use of only a three-level qutrit, the experimental setup is much simplified when compared with previous proposals requiring a four-level artificial atomic systems. Based on our Hamiltonian, we implement a two-resonator qubits controlled-phase gate and generate a two-resonator entangled coherent state. Numerical simulation shows that the high-fidelity implementation of the phase gate and creation of the entangled coherent state are feasible with current circuit QED technology.