Realization of a crosstalk-free two-ion node for long-distance quantum networking

TL;DR

This paper demonstrates a crosstalk-free two-ion quantum node compatible with telecom wavelengths, enabling long-distance quantum networking by entangling ions over 12 km fiber with minimal interference.

Contribution

First experimental implementation of a telecom-compatible, crosstalk-free quantum node using two trapped calcium ions with separate qubit encodings.

Findings

Successful ion-photon entanglement over 12 km fiber

Crosstalk-free operation between communication and memory qubits

Implementation of a quantum wavelength conversion module

Abstract

Trapped atomic ions constitute one of the leading physical platforms for building the quantum repeater nodes to realize large-scale quantum networks. In a long-distance trapped-ion quantum network, it is essential to have crosstalk-free dual-type qubits: one type, called the communication qubit, to establish an entangling interface with telecom photons; and the other type, called the memory qubit, to store quantum information immune from photon scattering under entangling attempts. Here, we report the first experimental implementation of a telecom-compatible and crosstalk-free quantum network node based on two trapped $^{40}$Ca$^{+}$ ions. The memory qubit is encoded on a long-lived metastable level to avoid crosstalk with the communication qubit encoded in another subspace of the same ion species, and a quantum wavelength conversion module is employed to generate ion-photon entanglement over a $12\,$km fiber in a heralded style. Our work therefore constitutes an important step towards the realization of quantum repeaters and long-distance quantum networks.