avatarJuan Moreno


A Year in Quantum Key Distribution: Groundbreaking Papers of 2023

In 2023, QKD has seen an alignment of theoretical advancements with practical applications, signaling a transition from lab-based experiments to real-world deployment. The research throughout the year paints a future where QKD is not just a scientific curiosity but a cornerstone of secure communication systems globally. The progress made in 2023 lays a solid foundation for the next steps in quantum cryptography, potentially leading to a paradigm shift in how we perceive and implement secure communications in an increasingly digital world.

January: Real-Time Parameter Monitoring in CV-QKD

Title: “Practical, high-speed Gaussian coherent state continuous variable quantum key distribution with real-time parameter monitoring, optimised slicing, and post-processed key distillation

This paper marks a significant advancement in CV-QKD by enhancing real-time parameter monitoring, optimized slicing, and post-processed key distillation. These developments are crucial for practical applications of QKD, offering more robust and efficient quantum communication systems​.

Details: The study delves into the minutiae of CV-QKD systems, focusing on excess noise values and the corresponding secure key rates. By implementing real-time monitoring and optimising slicing reconciliation, the research achieves greater accuracy and efficiency. This approach leads to a practical and high-speed Gaussian coherent state CV-QKD, which is a substantial step towards operational quantum communication networks.

I got initially interested on this paper because I was interested on a different type of monitoring, where I can send all the relevant data from any QKD system (like SKR or QBER) to a classical monitoring system for timeline series database, log analysis and graphs visualization. I’ve written about how to easily write CDK code to receive these metrics on Amazon EC2 instances and your own RDS database, but AWS supports managed Grafana and I still want to migrate my code an even simpler implementation where I don’t have to manage servers.

February: Breaking Speed Barriers in QKD

Title: “High-rate quantum key distribution exceeding 110 Mb/s

This paper is a trailblazer in QKD, setting new standards for speed by achieving over 110 Mb/s. This remarkable speed makes QKD more applicable to high-speed networks, paving the way for broader adoption​.

Details: The research addresses the challenge of achieving high-speed quantum key distribution, essential for integrating QKD into modern high-speed communication networks. The study demonstrates a QKD system capable of exceeding 110 Mb/s, which is a substantial leap from previous capabilities. This speed breakthrough is critical for making quantum encryption technologies more accessible and practical for widespread use in various high-speed applications.

I’m going to be honest here. My first thought was: “maybe we’ve found the perfect encryption here!” In my head, at 110 Mb/s we could use OTP to encrypt not only critical information like the rely of key material, but everything that travels inside the fiber. However, while these speeds are a significant step towards more practical and widespread use of quantum-secure communication methods, using this technology for OTP encryption of all data communication still faces considerable practical challenges. The current speed, although impressive, might not be sufficient for the vast bandwidth requirements of OTP for general data communication, especially when considering the additional challenges of key management and network limitations. This study probably used special low-loss cable neatly packed in a spool inside a lab, isolated from environmental factors like temperature fluctuations and physical vibrations. Also it didn’t need to worry about synchronization between sender and receiver, etc. You can find more operational considerations of implementing OTP in a previous post.

March: The Rise of Fully Passive QKD

Title: “Fully Passive Quantum Key Distribution

The introduction of a fully passive setup in QKD is a major innovation, greatly enhancing security and reliability by reducing active modulator side channels​.

Details: The paper presents a novel approach in the realm of QKD, introducing a fully passive linear optical QKD source. This passive system eliminates potential vulnerabilities associated with active modulators, thereby enhancing the overall security and reliability of QKD setups. The approach is a significant step forward in developing more secure and robust quantum communication systems.

This was an amazing discovery for me, because I had no idea that such systems existed prior to reading this paper. In a fully passive QKD system, there are no active components like modulators or switches that dynamically alter the state of the quantum signal during transmission. Instead, the system relies solely on passive optical elements like beam splitters, mirrors, and passive optical relays. The configuration of a passive QKD system is static once set up. Unlike active systems, where settings can be dynamically changed (like adjusting the phase or polarization of photons), passive systems don’t allow for such real-time adjustments. What this implies is that passive systems often depend on the intrinsic quantum properties of light, such as superposition and entanglement, without external manipulation. For example, they might use the random splitting of photons at a beam splitter as a fundamental element of the protocol. My very next question was why we are not seeing more of these devices as commercial off-the-shelf products: as I understand, passive systems can be more sensitive to environmental fluctuations, like temperature changes or vibrations, which can affect the alignment or phase stability of the optical setup… nothing that it’s ready today to be shipped or built at scale.

April: Satellite-Based QKD

Title: “Satellite-Based Quantum Key Distribution in the Presence of Bypass Channels

This research extends the horizon of QKD to satellite-based systems, addressing security in scenarios with restricted eavesdropping, and opening the door to global QKD networks​.

Details: The study explores the feasibility and security of satellite-based quantum communications, an area that has immense potential for establishing global quantum networks. The research presents new methodologies for ensuring secure communication in scenarios where eavesdropping restrictions are applicable, particularly in satellite settings. This paper paves the way for practical and efficient satellite-based QKD implementations, which is a significant step towards global quantum communication networks.

May: Generalised Entropy in QKD

Title: “Security of quantum key distribution from generalised entropy accumulation

This publication introduces a fresh perspective on QKD security protocols by focusing on entropy accumulation, an essential factor for robust quantum cryptography​.

Details: In this paper, the focus is on the concept of generalized entropy accumulation within the context of QKD. The study provides a novel framework for analyzing and ensuring the security of quantum key distribution systems. By leveraging the principles of entropy accumulation, the research offers deeper insights into the security mechanisms of QKD, enhancing the understanding and implementation of robust quantum cryptographic systems.

Entropy and its obvious connection with security is something that still need to dive into. I assume that the insights here are likely highly relevant to the use of QRNGs, a fundamental component of secure QKD systems, and understanding how this entropy accumulates and contributes to security is crucial. It goes to the bucket list for 2024.

June: Device-Independent QKD Advances

Title: “Advances in device-independent quantum key distribution

This paper highlights significant progress in MDI and TF QKD, pushing forward the frontiers of device independence in secure quantum communications​.

Details: The research delves into the advancements in measurement-device-independent (MDI) and twin-field (TF) QKD, two areas that are pivotal for enhancing the security and reliability of quantum communication systems. The paper discusses the latest breakthroughs in these fields, providing insights into how QKD can be made more secure and versatile by eliminating dependencies on the security of the devices used in quantum communication systems.

July: QKD in Packet-Switched Networks

Title: “Quantum key distribution in a packet-switched network

This paper explores the integration of QKD into modern packet-switched networks, a crucial step for marrying quantum security with current internet infrastructure​.

Details: The research addresses the practicality of implementing QKD in existing packet-switched networks. It discusses methods to ensure that QKD can coexist and operate effectively within the framework of modern digital communication systems. This is a significant step towards the practical application of quantum cryptography in everyday internet communication.

August: High Secret Key Rate’s Significance

Title: “High secret key rate goes a long way

Highlighting the importance of high secret key rates, this publication underscores a critical aspect of QKD’s practicality and scalability​.

Details: The paper emphasizes the importance of achieving high secret key rates in quantum key distribution. High secret key rates are essential for the practical deployment of QKD in various communication scenarios, making quantum encryption more viable and efficient for widespread use.

September: Hybrid Integrated QKD Transceiver Chip

Title: “A hybrid integrated quantum key distribution transceiver chip

This paper presents a groundbreaking development in QKD hardware with the introduction of a new hybrid integrated QKD transceiver chip​.

Details: The research introduces a novel hybrid integrated QKD transceiver chip, which combines several optical components into a single chip. This integration marks a significant advancement in the miniaturization and efficiency of QKD systems, making them more practical for a wider range of applications.

October: End-to-end Key Distribution in QKD Networks

Title: “How to Achieve End-to-end Key Distribution for QKD Networks in the Presence of Untrusted Nodes

This paper tackles the challenge of secure key distribution across QKD networks with untrusted nodes, crucial for the widespread deployment of QKD​.

Details: The study presents a method for achieving end-to-end key distribution in QKD networks, even when some nodes are untrusted. This is vital for the implementation of large-scale, secure quantum communication networks, as it ensures the integrity and security of the quantum keys throughout the network.

November: Information Reconciliation in CV-QKD

Title: “Information reconciliation of continuous-variables quantum key distribution: principles, implementations and applications

Offering a deep dive into information reconciliation in CV-QKD, this paper is key for ensuring secure quantum communication​.

Details: The paper provides a comprehensive analysis of the principles and implementations of information reconciliation in CV-QKD. This process is crucial for correcting errors in the quantum key distribution process, ensuring the reliability and security of the communication.

December: Device-Independent QKD Protocols Review

Title: “Security of device-independent quantum key distribution protocols: a review

This comprehensive review discusses the security aspects of device-independent QKD protocols, crucial for understanding the current challenges in QKD security​.

Details: The review offers a detailed analysis of the security of device-independent quantum key distribution protocols. It provides insights into the strengths and potential vulnerabilities of these protocols, offering a thorough understanding of the current state of QKD security.

Future Directions and Trends

Practical Implementation — The trend towards practical implementation and integration into existing infrastructures is evident. Research is shifting from theoretical frameworks to real-world applications, suggesting a future where QKD could become a standard for secure communications.

Technological Innovations — Advancements in QKD hardware, like integrated chips and passive setups, indicate a move towards more efficient, compact, and user-friendly QKD systems. This could lead to wider adoption in various sectors, from telecommunications to national security.

Expansion and Accessibility — The exploration of high-speed QKD and satellite-based systems opens the possibility of global quantum networks. This expansion could bring quantum-secure communication to a broader audience, transcending geographical limitations.

Security Focus — The continuous emphasis on device independence and novel security protocols reflects the field’s commitment to addressing and mitigating potential vulnerabilities. This focus is crucial for maintaining the integrity of quantum communications against evolving cyber threats.


In 2023, QKD has seen an alignment of theoretical advancements with practical applications, signaling a transition from lab-based experiments to real-world deployment. The research throughout the year paints a future where QKD is not just a scientific curiosity but a shifting paradigm of secure communication systems globally. The progress made in 2023 lays a solid foundation for the next steps in quantum cryptography, potentially leading to a paradigm shift in how we perceive and implement secure communications in an increasingly digital world. These are exciting times to be alive.

If you enjoyed this article, consider trying out the AI service I recommend. It provides the same performance and functions to ChatGPT Plus(GPT-4) but more cost-effective, at just $6/month (Special offer for $1/month). Click here to try ZAI.chat.

Recommended from ReadMedium