Breakthrough quantum key distribution system achieves unprecedented speeds using integrated photonics

A groundbreaking achievement has been made in the field of secure communication with the development of a quantum key distribution (QKD) system based on integrated photonics. This cutting-edge technology enables the transmission of highly secure keys at unprecedented speeds, marking a significant milestone towards the practical application of QKD in real-world scenarios.

QKD has long been recognized as a reliable method for establishing secret keys, ensuring secure communication between distant parties. By leveraging the quantum properties of light to generate random and unbreakable keys for data encryption and decryption, QKD relies on the fundamental laws of physics rather than computational complexity, which underpins today’s conventional communication protocols.

The research team, led by Hugo Zbinden from the University of Geneva in Switzerland, has successfully developed a QKD system using integrated photonics, wherein all system components are integrated onto chips, excluding the laser and detectors. This innovative approach offers numerous advantages, including compactness, affordability, and ease of large-scale production, making it a highly promising technology.

Rebecka Sax, a member of the research team from the University of Geneva, emphasized the importance of seamlessly integrating QKD into existing communication networks. She explained that the utilization of integrated photonics, which employs the same manufacturing processes as silicon computer chips, represents a crucial step towards achieving this goal.

While QKD already possesses immense potential for safeguarding sensitive applications such as banking, healthcare, and defense, its adoption has yet to reach widespread levels. Sax highlighted that this latest research provides strong evidence of the technology’s maturity and addresses the technical challenges associated with implementing QKD using optical integrated circuits. This advancement opens doors for its integration into various networks and applications, paving the way for enhanced security in the digital age.

Researchers have developed a quantum key distribution (QKD) system based on silicon photonics that can transmit secure keys at unprecedented speeds. The QKD transmitter (pictured) combines a photonic and electric integrated circuit with an external diode laser. Credit: Rebecka Sax, University of Geneva

Building a faster chip-based system

In earlier research, the scientists had developed a three-state time-bin QKD protocol and achieved remarkable transmission speeds using conventional fiber-based components.

Sax explained that their objective in this new study was to implement the same protocol utilizing integrated photonics. By employing an integrated photonic system, the researchers benefited from its compactness, durability, and ease of manipulation. Furthermore, the reduced number of components simplified the implementation process and troubleshooting in network settings, thereby enhancing the viability of QKD for secure communication.

The QKD system consists of a transmitter responsible for sending encoded photons and a receiver designed to detect these photons. To realize their goals, the University of Geneva team collaborated with Sicoya GmbH, a silicon photonics company based in Berlin, Germany, and ID Quantique, a quantum cybersecurity company located in Geneva. Together, they developed a silicon photonics transmitter by combining a photonic integrated circuit with an external diode laser.

The receiver, fabricated by Roberto Osellame’s group at the CNR Institute for Photonics and Nanotechnology in Milano, Italy, was constructed from silica. It comprised a photonic integrated circuit and two external single-photon detectors. The fabrication process involved femtosecond laser micromachining.

Sax highlighted the significance of using an external laser and a photonic-electronic integrated circuit in the transmitter, as it enabled the precise production and encoding of photons at an exceptional speed of up to 2.5 GHz. On the receiver side, a polarization-independent and low-loss photonic integrated circuit, in conjunction with external detectors, facilitated the passive and straightforward detection of transmitted photons. By connecting these two components using standard single-mode fiber, high-speed generation of secure keys became achievable.

Low-loss, high-speed transmission

Following a comprehensive characterization of the integrated transmitter and receiver, the researchers proceeded to conduct secret key exchanges under various simulated fiber distances. They successfully achieved key exchange over a 150-km long single-mode fiber using single-photon avalanche photodiodes, which are well-suited for real-world applications.

Furthermore, the team performed experiments utilizing single-photon superconducting nanowire detectors, which yielded an impressively low quantum bit error rate of only 0.8%. The receiver not only achieved polarization independence, a challenging feat in integrated photonics, but also exhibited remarkably low loss, measuring around 3 dB.

Sax emphasized that these new experiments yielded secret key rates and quantum bit error rates comparable to previous studies employing fiber-based components. However, the QKD system presented a significantly simplified and more practical setup, showcasing the feasibility of implementing this protocol with integrated circuits.

Moving forward, the researchers are focused on packaging the various system components into a straightforward rack enclosure, enabling seamless integration of QKD into network systems. This advancement brings QKD closer to real-world deployment and underscores its potential as a secure communication solution.

Source: Optica

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