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Bonn Team’s Technology Brings Quantum Networks Closer to Reality

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BONN, Germany, March 22, 2021 — Researchers from the University of Bonn demonstrated quantum entanglement between a stationary qubit and a photon with direct coupling to an optical fiber. The work represents a major step toward the realization of quantum networks and, from them, secure data transmission.

Quantum networks necessitate stationary qubits be entangled with the communication channel, typically consisting of photons. A quantum state cannot be copied and transmitted in a classical sense. Photons, though difficult to store, are typically favored for transmission in quantum communication applications, both those that are in practice and those that are theoretical, due to their speed.

“The implementation of efficient interfaces between photons and stationary qubits is therefore crucial for the rate of information transfer and the scalability of a quantum network,” said first author Pascal Kobel, a Ph.D. student in the experimental quantum physics research group at the University of Bonn.

The team’s configuration used a Fabry-Pérot cavity — an optical resonator consisting of two opposing concave mirrors situated on the end facets of two optical fibers to which team members applied a reflective coating.

“The construction and combination of such a resonator with a single ion is experimentally challenging. Fibers and ion have to be placed with a relative accuracy of about one micrometer to each other,” said co-author Moritz Breyer, a physicist in Michael Köhl’s research group at Bonn. The small resonator volume, however, increases the light-matter interaction, enabling high bandwidths for the distribution of quantum information in a network. It also allows for the intrinsic coupling of photons to optical fibers, which simplifies their distribution in a given network.

In the experimental setup, at a distance of 1.5 m, the single ytterbium ion and the photon shared a common entangled quantum state.

“Our presented system is well suited as a node in quantum networks,” Köhl said.

The researchers intend to further develop their system by improving the stability of the light-matter interface and using the setup for the distribution of quantum keys. The study may hold relevance for distributed quantum computing or provably secure communication.

The research was published in npj Quantum Information (www.doi.org/10.1038/s41534-020-00338-2).



Published: March 2021
Glossary
quantum
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
node
In a communications network, a point at which data are received or from which they are sent. Though the term often is used synonymously with workstation, interconnection points in a network also are called nodes.
quantum key distribution
Quantum key distribution (QKD) is a method of secure communication that utilizes principles from quantum mechanics to establish a shared secret key between two parties, typically referred to as Alice and Bob, while detecting any potential eavesdropping attempts by a third party, commonly known as Eve. The fundamental principle behind QKD is the use of quantum properties, such as the superposition principle and the no-cloning theorem, to enable the distribution of cryptographic keys in a...
Research & Technologyquantumentanglementquantum networkmemorynodeUniversity of BonnEuropequantum computingquantum keyquantum key distributionnpj Quantum InformationFabry-PerotFabry-Pérot

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