Generating entangled states from coherent states in circuit-QED

TL;DR

This paper presents a two-step protocol for efficiently generating Bell and NOON entangled states of microwave resonators from coherent states using superconducting qutrits, with analysis of robustness and extensions.

Contribution

The authors develop a novel, effective Hamiltonian-based method for creating bipartite entangled states in circuit-QED systems from coherent states, including robustness analysis.

Findings

Successful generation of Bell and NOON states from coherent states.

Protocol robustness against systematic errors and decoherence.

Extension of the protocol to a $\\Xi$-type qutrit scenario.

Abstract

Entangled states are self-evidently important to a wide range of applications in quantum communication and quantum information processing. We propose an efficient and convenient two-step protocol for generating Bell states and NOON states of two microwave resonators from merely coherent states. In particular, we derive an effective Hamiltonian for resonators coupled to a superconducting $\Lambda$-type qutrit in the dispersive regime. By the excitation-number-dependent Stark shifts of the qutrit transition frequencies, we are able to individually control the amplitudes of specified Fock states of the resonators associated with relevant qutrit transition, using carefully tailored microwave drive signals. Thereby an arbitrary bipartite entangled state in Fock space can be generated by a typical evolution-and-measurement procedure. We analysis the undesired state transitions and the robustness of our protocol against the systematic errors from the microwave driving intensity and frequency, the quantum decoherence of all components, and the crosstalk of two resonators. In addition, we demonstrate that our protocol can be extended to a similar scenario with a $\Xi$-type qutrit.