Entanglement between a trapped ion qubit and a 780-nm photon via quantum frequency conversion

TL;DR

This paper demonstrates entanglement between a trapped ion and a 780 nm photon through quantum frequency conversion, enabling hybrid quantum networks with reduced losses and compatibility with existing quantum devices.

Contribution

It introduces a method to generate ion-photon entanglement at 780 nm by frequency converting entangled photons from a barium ion, maintaining high fidelity.

Findings

Achieved ion-photon entanglement with fidelities ≥ 0.93 at 493 nm and ≥ 0.84 at 780 nm.

Successfully used quantum frequency conversion to match photon wavelength with quantum network devices.

Identified detector noise as a primary factor in fidelity reduction at 780 nm.

Abstract

Future quantum networks will require the ability to produce matter-photon entanglement at photon frequencies not naturally emitted from the matter qubit. This allows for a hybrid network architecture, where these photons can couple to other tools and quantum technologies useful for tasks such as multiplexing, routing, and storage, but which operate at wavelengths different from that of the matter qubit source, while also reducing network losses. Here, we demonstrate entanglement between a trapped ion and a 780 nm photon, a wavelength which can interact with neutral-Rb-based quantum networking devices. A single barium ion is used to produce 493 nm photons, entangled with the ion, which are then frequency converted to 780 nm while preserving the entanglement. We generate ion-photon entanglement with fidelities $\geq$ 0.93(2) and $\geq$ 0.84(2) for 493 nm and 780 nm photons respectively with the fidelity drop arising predominantly from a reduction in the signal-noise of our detectors at 780 nm compared with at 493 nm.