Generating Bell states and $N$-partite $W$ states of long-distance qubits in superconducting waveguide QED

TL;DR

This paper proposes a method to generate long-distance entangled Bell and W states of superconducting qubits in a waveguide QED system, enabling robust quantum networking with long-lived entanglement.

Contribution

The paper introduces a novel scheme for creating dark-state Bell and W states of superconducting qubits in waveguide QED, extending to multi-qubit systems with potential for long-distance quantum communication.

Findings

Bell states can be prepared as dark states with proper parameters.

W states of multiple qubits can be generated and are also dark states.

Decoherence limits the lifetime of the generated entangled states.

Abstract

We show how to generate Bell states and $N$-partite $W$ states of long-distance superconducting (SC) qubits in a SC waveguide quantum electrodynamical (QED) system, where SC qubits are coupled to an open microwave transmission line. In the two-qubit case, the Bell state of two long-distance qubits can be a dark state of the system by choosing appropriate system parameters. If one proper microwave pulse drives one of two qubits, the two qubits will evolve from their ground states to a Bell state. Further, we extend this scheme to the multi-qubit case. We show that $W$ states of $N$ long-distance qubits can also be generated. Because both the Bell and $W$ states are decoupled from the waveguide (i.e., dark states of the system), they are steady and have very long lifetimes in the ideal case without decoherence of qubits. In contrast to the ideal case, the presence of decoherence of qubits limits the lifetimes of the Bell and $W$ states. Our study provides a novel scheme for generating Bell states and $N$-partite $W$ states in SC waveguide QED, which can be used to entangle long-distance nodes in waveguide quantum networks.