Chip-based Quantum Key Distribution (1509.00768v1)

Abstract: Improvement in secure transmission of information is an urgent practical need for governments, corporations and individuals. Quantum key distribution (QKD) promises security based on the laws of physics and has rapidly grown from proof-of-concept to robust demonstrations and even deployment of commercial systems. Despite these advances, QKD has not been widely adopted, and practical large-scale deployment will likely require integrated chip-based devices for improved performance, miniaturisation and enhanced functionality, fully integrated into classical communication networks. Here we report low error rate, GHz clocked QKD operation of an InP transmitter chip and a SiO$_x$N$_y$ receiver chip --- monolithically integrated devices that use state-of-the-art components and manufacturing processes from the telecom industry. We use the reconfigurability of these devices to demonstrate three important QKD protocols --- BB84, Coherent One Way (COW) and Differential Phase Shift (DPS) --- with performance comparable to state-of-the-art. These devices, when combined with integrated single photon detectors, satisfy the requirements at each of the levels of future QKD networks --- from point-of-use through to backbone --- and open the way to operation in existing and emerging classical communication networks.

• The paper presents a chip-based quantum key distribution system integrating InP transmitter and SiOxNy receiver chips.
• It achieves GHz clock rates and low quantum bit error rates across protocols like BB84, COW, and DPS with up to 568 kbps secret key rate.
• Its scalable, telecom-compatible design paves the way for integrating quantum and classical networks in secure communications.

Chip-based Quantum Key Distribution: Integrated Photonic Devices for Secure Communications

The paper "Chip-based Quantum Key Distribution," authored by Sibson et al., presents a significant advancement in the integration of quantum key distribution (QKD) technology. By developing chip-based solutions, the research addresses the challenges of scalability and integration with classical communication networks. This work is crucial for enabling the broad deployment of QKD, which is inherently secure based on quantum physics principles.

Technical Summary

This research demonstrates the development of monolithically integrated QKD devices using an indium phosphide (InP) transmitter chip and a silicon oxynitride (SiO$_x$N$_y$) receiver chip. These systems utilize the manufacturing processes prevalent in the telecom industry, providing a compact, robust, and scalable solution. The chips operate at GHz clock rates and exhibit low quantum bit error rates (QBER), showcasing performance metrics that match current state-of-the-art QKD systems.

The transmitter chip utilizes integrated laser sources, optical interferometers, and electro-optic phase modulators, all fabricated on the InP platform that supports high-speed active electro-optic components. Conversely, the receiver chip, built on the SiO$_x$N$_y$ platform, employs thermo-optic phase shifters for tuning and delay lines for protocol compatibility, optimized for low optical loss and small footprint. Together, these integrated devices perform well across different QKD protocols, specifically BB84, Coherent One-Way (COW), and Differential Phase Shift (DPS), with secret key rates achieving up to 568 kbps for a simulated 20 km fiber link.

Implications and Future Directions

The integration of QKD with microelectronic fabrication techniques has several significant implications for future communications systems. Firstly, the scalability and integration with existing systems can lead to the widespread adoption of QKD by reducing both the size and cost of deployment. As QKD becomes integrated into hand-held and field-deployable devices, or implemented for securing the Internet of Things (IoT), these features are crucial for its applicability.

Additionally, these integrated devices pave the way for unified quantum and classical network operations, ideally configured through software rather than hardware. The reconfigurability of the demonstrated devices supports multi-protocol operations and opens new avenues for implementing advanced, secure communication protocols, such as reference-frame independent and measurement-device independent QKD.

The results achieved could also guide advancements in network capacity by employing wavelength division multiplexing, thereby increasing the quantum communication bandwidth. Furthermore, the ongoing development of integrated photonic systems will likely enable higher levels of sophistication necessary for comprehensive inter-network security against side-channel attacks.

In conclusion, the paper outlines a crucial step toward practical, widespread deployment of quantum cryptographic systems by demonstrating chip-based QKD implementation. The integration of these devices into existing telecommunications infrastructure, alongside continued advancements in photonic technology, heralds a future where secure quantum communications can be mainstream, versatile, and adaptive, grounded firmly in the principles of quantum mechanics.