12 Jan. Advancing towards a global quantum network
Quantum networks can make communication extremely secure. Moreover, they can link remote quantum computers together to create a single, more powerful computing machine. Quantum networks can also serve as the basis for highly accurate distributed sensor systems for time measurement or environmental monitoring. These networks require so-called quantum network nodes that can store quantum information and exchange it optically. A team led by Ben Lanyon at the Institute of Experimental Physics, University of Innsbruck, Austria, has now demonstrated such a network node based on a prototype ion-trap quantum computer with ten qubits. It does work by precisely modifying the electric fields to move individual calcium ions into an optical resonator. There, a precisely tuned laser pulse triggers the emission of a single photon whose polarization is entangled with the state of the ion.
(a) Concept image. Each 854 nm photon is polarization-entangled with a matching-colored 40 Ca+ ion (color indicates entanglement only). (b) Enlargement showing 854 nm vacuum cavity standing waves and 85.9° angle to ion string (dashed line). (c) Atomic energy level diagram. (d) The ion string is stepwise displaced along its axis, bringing ions one at a time to the cavity center and standing wave maximum. Image: Phys. Rev. Lett. 135, 080801
Highly scalable quantum entanglement
The method produces a photon chain in which each photon is entangled with a distinct ion qubit in the register. In the future, the photons could be transmitted to distant network nodes, thereby creating entanglement between spatially separated quantum computers. The research team reports an average ion-photon entanglement quality of 92% in the experiment; an accuracy that underlines the robustness of this method. “One of the greatest strengths of this method is its scalability,” says Lanyon. “While previous experiments could only connect two or three ion qubits with single photons, our approach can be extended to much larger registers that could potentially contain hundreds of ions and more.” This paves the way for networking entire quantum processors across laboratories or even continents.
“Our method is a step toward larger and more complex quantum networks,” says Marco Canteri, the study’s first author. “It brings us closer to practical applications such as quantum-secure communication, distributed quantum computing, and large distributed quantum sensing.”
The researchers also point out that this technology could improve optical atomic clocks. Connected worldwide via quantum networks, they could form a time measurement system of unprecedented accuracy.
Original publication
[M. Canteri et al.: Photon-Interfaced
Ten-Qubit Register of Trapped Ions;
Phys. Rev. Lett. 135, 080801, 2025,
DOI 10.1103/v5k1-whwz]
Source: www.uibk.ac.at
Image: : Harald Ritsch / University of Innsbruck