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IEEE Transactions on Quantum Engineering

A Low-Cost, Off-the-Shelf Quantum Key Distribution System With kbit/s Key Generation Rates

Fabian Klingmann, Kriti Dutta, Mira Stephan, Max Haymann-Pohl, Lorenz Reuschel, Alexander Noack, René Kirrbach, Jingzhong Yang, Dr. Fei Ding

Published Jan 1, 2026• 0 citations
Publisher

Abstract

Commercial quantum key distribution (QKD) systems are currently very expensive and usually come as large server rack components. Thus, their application is still very limited and adoption in practical implementations has not happened yet. One reason for the high price and large size is the use of high-end and custom-built hardware. We present for the first time a QKD system that runs an entire BB84 protocol on two microcontrollers and is built from off-the-shelf components. The system includes polarization compensation and postprocessing. It creates secret keys at key rates of up to 1.36 kbit/s. With this system we show that the execution of a QKD protocol is not limited to high-performance hardware. This marks a breakthrough on the way towards an affordable, scalable QKD system that can be easily integrated into existing hardware.

DOI
10.1109/tqe.2026.3733725

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Commercial quantum key distribution (QKD) systems are currently very expensive and usually come as large server rack components. Thus, their application is still very limited and adoption in practical implementations has not happened yet. One reason for the high price and large size is the use of high-end and custom-built hardware. We present for the first time a QKD system that runs an entire BB84 protocol on two microcontrollers and is built from off-the-shelf components. The system includes polarization compensation and postprocessing. It creates secret keys at key rates of up to 1.36 kbit/s. With this system we show that the execution of a QKD protocol is not limited to high-performance hardware. This marks a breakthrough on the way towards an affordable, scalable QKD system that can be easily integrated into existing hardware.
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We report on a BB84 decoy-state quantum key distribution (QKD) system constructed using commercial off-the-shelf (COTS) components. Four 794 nm vertical-cavity surface-emitting lasers (VCSELs) are current-modulated at 10 MHz rate with three power levels to form a decoy state transmitter. The COTS VCSELs exhibit long term stability with high polarization extinction ratio, narrow band operation (sub-nanometer bandwidth), and wavelength tunability and stability suitable for constructing four indistinguishable qubit channels. A 780 nm, 10 MHz time-transfer channel is used for transferring the timing information along with a start and end marker for the qubit transfer period. Internally-developed transmitter laser drivers and receiver detectors are controlled and read out with COTS system-on-chip (SoC) boards. We obtain a nominal bit-error-rate (BER) of ~4% for the system. We also report on the development of a synchronous (100 MHz) single photon detector for increasing the repetition rate of our QKD system. This work shows promise for building a COTS-based, small size, weight, and power hardware for space applications.
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The security of conventional cryptography systems is threatened in the forthcoming era of quantum computers. Quantum key distribution (QKD) features fundamentally proven security and offers a promising option for quantum-proof cryptography solution. Although prototype QKD systems over optical fiber have been demonstrated over the years, the key generation rates remain several orders of magnitude lower than current classical communication systems. In an effort toward a commercially viable QKD system with improved key generation rates, we developed a discrete-variable QKD system based on time-bin quantum photonic states that can generate provably secure cryptographic keys at megabit-per-second rates over metropolitan distances. We use high-dimensional quantum states that transmit more than one secret bit per received photon, alleviating detector saturation effects in the superconducting nanowire single-photon detectors used in our system that feature very high detection efficiency (of more than 70%) and low timing jitter (of less than 40 ps). Our system is constructed using commercial off-the-shelf components, and the adopted protocol can be readily extended to free-space quantum channels. The security analysis adopted to distill the keys ensures that the demonstrated protocol is robust against coherent attacks, finite-size effects, and a broad class of experimental imperfections identified in our system.
Quantum key distribution (QKD) provides information-theoretic security independent of computational assumptions, yet the bulk and cost of current systems hinder large-scale deployment. Although integrated photonic technologies have enabled highly integrated QKD chips, practical QKD transmitters are still predominantly implemented as rack-mounted systems. Here, we demonstrate a highly integrated standalone QKD transmitter that integrates all essential functionalities required for practical QKD operation within a compact platform built around a silicon photonic encoding chip. The transmitter occupies only 167×56×21 mm3167 \times 56 \times 21~\mathrm{mm}^3167×56×21 mm3 (∼0.2 dm3\sim 0.2~\mathrm{dm}^3∼0.2 dm3), comparable in size to a half-height, half-width PCIe card and more than 30 times smaller in volume than a conventional 1U rack-mounted system. Paired with a conventional discrete-component receiver, it achieves a secure key rate of 219.1 kbps over 51.3 km of standard single-mode fiber, with performance comparable to that of conventional discrete-component implementations. This work bridges the gap between photonic chip integration and deployable QKD hardware, marking an important step toward transitioning QKD transmitters from conventional rack-mounted equipment to compact board-level platforms.
Quantum Key Distribution (QKD) consists in the exchange of a secrete key between two distant points [1]. Even if quantum key distribution systems exist and commercial systems are reaching the market [2], there are still improvements to be made: simplify the construction of the system; increase the secret key rate. To this end, we present a new protocol for QKD tailored to work with weak coherent pulses and at high bit rates [3]. The advantages of this system are that the setup is experimentally simple and it is tolerant to reduced interference visibility and to photon number splitting attacks, thus resulting in a high efficiency in terms of distilled secret bits per qubit. After having successfully tested the feasibility of the system [3], we are currently developing a fully integrated and automated prototype within the SECOQC project [4]. We present the latest results using the prototype. We also discuss the issue of the photon detection, which still remains the bottleneck for QKD.