Quantum network progress: Erbium atoms emit single photons

Researchers at the Max Planck Institute of Quantum Optics (MPQ) and the Technical University of Munich (TUM) in Garching have made significant progress in the development of quantum networks. By exciting erbium atoms embedded in crystalline silicon, they have successfully generated single photons with unique properties, paving the way for the future quantum internet.

This breakthrough allows for the exchange of information through fiber-optic networks with guaranteed privacy and security. The researchers’ novel system offers advantages in terms of producing network nodes, their cooling, and the range of data transmission.

The controlled utilization of quantum phenomena, such as particle entanglement, opens up new possibilities for various technical applications. This includes the creation of highly sensitive quantum sensors and fast quantum computers, capable of solving problems that are currently beyond the reach of conventional computing machines.

The potential of these quantum technologies can be fully realized within quantum networks. The recent study conducted by the MPQ and TUM team demonstrates a promising platform for building such networks. The researchers have achieved the controlled emission of individual photons from excited erbium atoms, which possess properties ideal for constructing quantum networks.

According to team leader Prof. Dr. Andreas Reiserer, all quantum technologies rely on qubits, which are the fundamental carriers of quantum information. By connecting qubits through light, similar to the way the classical internet functions, a quantum network can be established. In this case, the qubits can be individual atoms isolated from each other and embedded in a solid host material.

The researchers’ successful manipulation of erbium atoms within a silicon crystal represents a significant advancement. The emission of individual photons with desirable properties brings us closer to realizing the potential of quantum networks for various applications. The details of this research can be found in the journal Optica.

Ideal conditions for telecommunications

To achieve their goal, Reiserer’s team employed a technique known as doping, wherein they implanted erbium atoms into specific positions within the silicon crystal lattice. This process endowed the erbium atoms with remarkable optical properties, causing them to emit light at a wavelength of 1,536 nanometers. This wavelength closely matches that used in classical fiber optic networks for data transmission, as it exhibits minimal signal loss. Consequently, this enables the transmission of quantum information over long distances, as Reiserer points out.

However, in order to harness the potential of erbium’s optical properties, it is crucial to stimulate the atoms to emit individual light particles under controlled conditions. Andreas Gritsch, a doctoral researcher in Reiserer’s team, explains that this allows for the creation of an interface for sending and receiving quantum information.

The researchers in Garching and Munich have successfully accomplished this task using an optical resonator, a device capable of reflecting and amplifying light. Significantly, they have developed a resonator composed of silicon doped with erbium—a remarkable achievement in itself.

In summary, the team has made strides in their research by strategically implanting erbium atoms into silicon crystals, capitalizing on the atoms’ optical properties. Through the utilization of an erbium-doped silicon resonator, they have successfully stimulated the emission of individual light particles, establishing a crucial interface for quantum information transmission.

Nanophotonic resonator on a silicium chip. Credit: MPQ

A light amplifier in nano format

In contrast to typical optical resonators that employ mirrors, the resonator utilized by the researchers had a distinctive structure made of crystalline silicon. This structure consisted of regularly arranged nanoscale holes within the material. Despite its small dimensions (only a few micrometers in total), the resonator contained a few dozen erbium atoms. Coupled with an optical fiber, the nanophotonic resonator allowed laser light to enter and excite the atoms, resulting in the emission of individual photons with the desired characteristics.

This breakthrough provides a means to generate qubits specifically for transporting quantum information. The use of crystalline silicon for this purpose presents an advantage due to its extensive history of application in the production of semiconductor components like microchips for computers, smartphones, and navigation devices. The well-established manufacturing techniques and processes within the semiconductor industry make it feasible to produce high-quality and pure silicon crystals at a low cost.

Another noteworthy aspect of the system developed by the MPQ and TUM scientists is the excellent optical properties exhibited by the erbium atoms embedded in silicon. These properties persist not only at extremely low temperatures near absolute zero (-273°C) but also at temperatures slightly above this threshold, up to eight degrees higher. Reiserer highlights the significance of these few degrees, as they can be readily achieved through cooling using a cryostat with liquid helium. This achievement contributes to the practicality and feasibility of implementing these technologies.

The potential applications of quantum networks are particularly appealing to entities dealing with sensitive data, such as financial institutions, medical facilities, and government agencies. While conventional encryption methods cannot ensure complete security, a quantum network would provide flawless data protection. If an eavesdropper attempted to intercept information transmitted via prepared photons, the quantum properties would be lost, rendering the data unusable.

In conclusion, the MPQ and TUM researchers have made significant progress in developing quantum networks by leveraging the unique properties of erbium atoms embedded in crystalline silicon. Their innovative resonator design and compatibility with silicon manufacturing processes offer promising prospects for quantum technology applications. The potential for secure data transmission has garnered interest from various sectors, where the protection of sensitive information is paramount.

Source: Max Planck Society

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