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Ad-hoc hybrid-heterogeneous metropolitan-range quantum key distribution network

Matthias Goy, Jan Krause, Ömer Bayraktar, Philippe Ancsin, Florian David, Thomas Dirmeier, Nico Doell, Jansen Dwan, Friederike Fohlmeister, Ronald Freund, Thorsten A. Goebel, Jonas Hilt, Kevin Jaksch, Oskar Kohout, Teresa Kopf, Andrej Krzic, Markus Leipe, Gerd Leuchs, Christoph Marquardt, Karen L. Mendez, Anja Milde, Sarika Mishra, Florian Moll, Karolina Paciorek, Natasa Pavlovic, Stefan Richter, Markus Rothe, René Rüddenklau, Gregor Sauer, Martin Schell, Jan Schreck, Andy Schreier, Sakshi Sharma, Simon Spier, Christopher Spiess, Fabian Steinlechner, Andreas Tünnermann, Hüseyin Vural, Nino Walenta, Stefan Weide

TL;DR

The paper tackles the challenge of rapidly deploying secure quantum communication across metropolitan-scale networks by integrating heterogeneous fiber and free-space channels with both trusted and untrusted nodes. It introduces a three-layer, crypto-agile architecture featuring quantum-secure gateways and a global key-management system, enabling key relays and inter-domain interoperability for diverse QKD protocols. Through a Jena testbed, it demonstrates practical ad-hoc deployments of DV-QKD, BBM92, HD-QKD, and CV-QKD across direct fiber, free-space, and fixed wireless fiber links, including a trusted-node demonstration and a quantum-secure link to a cloud service. The work shows that portable FSO terminals and modular QKD subsystems can form flexible metropolitan networks that deliver quantum-secure keys to real-world applications, with implications for disaster response and cloud security.

Abstract

This paper presents the development and implementation of a versatile ad-hoc metropolitan-range Quantum Key Distribution (QKD) network. The approach presented integrates various types of physical channels and QKD protocols, and a mix of trusted and untrusted nodes. Unlike conventional QKD networks that predominantly depend on either fiber-based or free-space optical (FSO) links, the testbed presented amalgamates FSO and fiber-based links, thereby overcoming some inherent limitations. Various network deployment strategies have been considered, including permanent infrastructure and provisional ad-hoc links to eradicate coverage gaps. Furthermore, the ability to rapidly establish a network using portable FSO terminals and to investigate diverse link topologies is demonstrated. The study also showcases the successful establishment of a quantum-secured link to a cloud server.

Ad-hoc hybrid-heterogeneous metropolitan-range quantum key distribution network

TL;DR

The paper tackles the challenge of rapidly deploying secure quantum communication across metropolitan-scale networks by integrating heterogeneous fiber and free-space channels with both trusted and untrusted nodes. It introduces a three-layer, crypto-agile architecture featuring quantum-secure gateways and a global key-management system, enabling key relays and inter-domain interoperability for diverse QKD protocols. Through a Jena testbed, it demonstrates practical ad-hoc deployments of DV-QKD, BBM92, HD-QKD, and CV-QKD across direct fiber, free-space, and fixed wireless fiber links, including a trusted-node demonstration and a quantum-secure link to a cloud service. The work shows that portable FSO terminals and modular QKD subsystems can form flexible metropolitan networks that deliver quantum-secure keys to real-world applications, with implications for disaster response and cloud security.

Abstract

This paper presents the development and implementation of a versatile ad-hoc metropolitan-range Quantum Key Distribution (QKD) network. The approach presented integrates various types of physical channels and QKD protocols, and a mix of trusted and untrusted nodes. Unlike conventional QKD networks that predominantly depend on either fiber-based or free-space optical (FSO) links, the testbed presented amalgamates FSO and fiber-based links, thereby overcoming some inherent limitations. Various network deployment strategies have been considered, including permanent infrastructure and provisional ad-hoc links to eradicate coverage gaps. Furthermore, the ability to rapidly establish a network using portable FSO terminals and to investigate diverse link topologies is demonstrated. The study also showcases the successful establishment of a quantum-secured link to a cloud server.

Paper Structure

This paper contains 27 sections, 15 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Architecture
  3. Service Layer - Quantum-Secure Gateway
  4. Key Management Layer
  5. Quantum Layer - Quantum Key Distribution
  6. Subsystems
  7. FSO terminals for ad-hoc urban links
  8. Transportable FSO terminal TFT-1
  9. Transportable FSO terminal TFT-2
  10. Transportable terminal QuBUS
  11. QKD systems
  12. Time-bin BB84 DV-QKD at 1550 nm
  13. BBM92-QKD at 1550 nm
  14. High-dimensional time-bin QKD at 1550 nm
  15. Free-space CV-QKD at 810 nm
  16. ...and 12 more sections

Figures (15)

  • Figure 1: System architecture underlying the following experiments. Red background: Trusted node; Dashed lines: Path of cryptographic keys; Solid lines: Authenticated communication (black), quantum channel (red), quantum-secure communication (green); LAN: Local area network; Q-GW: Quantum gateway; KMS: Key management system; GKMS: Global KMS; $\mathrm{KMS}_\mathrm{PQC}$: KMS for keys produced by post-quantum cryptography algorithms; $\mathrm{KMS}_\mathrm{QKD}$: KMS for QKD keys; $\mathrm{KXX}_\mathrm{TN}$: Trusted node key relay; QKD$_i$: Quantum key distribution node $i$.
  • Figure 2: Left: Transportable FSO terminal 1 (TFT-1) mounted on a motorized telescope tripod. Right: QuBUS with periscope assembly on its roof (cf. Sec. \ref{['sec:subsystems:fso-terminals:QuBUS']}).
  • Figure 3: Left: Design of the transportable FSO terminal 2 (TFT-2). Right: Architecture of the pointing, acquisition ant tracking (PAT) system for TFT-2. The PAT system consists of multiple control loops running in parallel. The coarse pointing assembly (CPA) driver features an internal servo control for disturbance rejection. The position-sensitive device (PSD) is used to close the optical loop for the coarse alignment of the CPA to the fine-pointing assembly (FPA) during acquisition and for the fine pointing loop during the tracking phase. An additional integral controller offloads the low-passed FPA angles to the CPA, whenever a predefined threshold is exceeded. NFOV: Narrow field of view; GUI: Graphical user interface.
  • Figure 4: System design of the 1-decoy time-bin BB84 QKD system from Fraunhofer HHI (BB84-QKD). ATT: Fix attenuator; BPF: Band-pass filter; BS: Beam splitter; DFB: Distributed-feedback laser; DLI: Delay-line interferometer; FPGA: Field-programmable gate array; IM: Intensity modulator; ISO: Isolator; KMS: Key-management system; PIN: Photodiode; PM: Phase modulator; QRNG: Quantum random number generator; Rb Clock: Rubidium atomic clock without GPS link; SPAD: Single-photon avalanche diode; TDC: Time-to-digital converter; VOA: Variable optical attenuator.
  • Figure 5: Entanglement-based QKD. (a) The entangled photon pair source (EPS) consists of a ppLN waveguide that is pumped bidirectionally in a Sagnac loop with a 775 nm continuous-wave laser. Two entangled photons are generated at a center wavelength of 1550 nm via type-0 spontaneous parametric down-conversion. (b) The EPS transmits the photons to the receiver Alice in the same building and receiver Bob in a neighboring building. (c) The polarization of the light is detected in a polarization analysis module. BS: beam splitter; HWP: half-wave plate; PBS: polarizing beam splitter; SNSPD: superconducting nanowire single photon detector.
  • ...and 10 more figures