Researchers achieve record secret key rates with new quantum communication technology
9 October 2024
A team of QSNP researchers from the Technical University of Denmark and Ghent University-IMEC have achieved a ground-breaking milestone in quantum communication, setting a new record for secure key exchange rates using an integrated photonic-electronic receiver and advanced digital signal processing for continuous-variable quantum key distribution (CV-QKD). This technological leap holds significant promise for bringing a new era of ultra-secure and high-speed quantum communication systems.
The research, published in Optica last August, outlines the development of a CV-QKD system that overcomes limitations of our current systems by using an innovative integrated photonic-electronic receiver. This receiver merges a silicon photonic integrated circuit, featuring a phase-diverse receiver, with custom-designed gallium arsenide phosphide high electron mobility transistor (GaAs pHEMT) transimpedance amplifiers. By leveraging high-speed integrated components and a low-noise design, the receiver achieves a remarkable shot-noise-limited bandwidth of over 20 GHz, enabling the system to operate at a classical telecom symbol rate of 10 GBaud.
This impressive speed translates to unprecedented secret key rates. The team achieved secret key rates exceeding 0.7 Gb/s over a 5 km distance and 0.3 Gb/s over a 10 km distance. The secret keys generated by this system are secure against collective attacks, even when considering finite-size effects in the parameter estimation, thanks to a well-designed digital signal processing pipeline that enables broadband system operation.
Breaking barriers and reducing costs
Existing high-rate CV-QKD systems have largely been limited to symbol rates of 5 GBaud. This new system effectively doubles that rate by enhancing the overall system bandwidth through the innovative integrated receiver and a meticulously designed digital signal processing (DSP) pipeline on the transmitter side. This achievement paves the way for even faster and more efficient quantum communication systems in the future. Using silicon photonics for CV-QKD systems allows for miniaturization and leverages existing CMOS manufacturing infrastructure, enabling mass production and significantly reducing costs. This is a crucial step toward making quantum communication technology commercially viable and accessible for wider adoption. The increased secret key rates offered by this system open up possibilities for high-data-rate applications such as real-time one-time-pad secured video encryption, distributed storage encryption, and high-speed access networks.
Looking ahead
While this breakthrough represents an advancement in CV-QKD, the researchers have identified some areas for further development:
- Extending composable security proofs: Currently, applying existing numerical security proofs for simpler to more complex modulation constellations, such as the 64 QAM used in this system, is computationally demanding. Developing more efficient and robust security proofs is essential for guaranteeing long-term security.
- Enhancing system stability: Integrating fibre attachment directly to the photonic chip in future receiver iterations would enhance system stability by reducing the impact of external factors such as temperature variations and mechanical drifts.
- Increasing the symbol rate: The researchers believe the system’s symbol rate can be further increased by fully utilizing the receiver’s impressive bandwidth. This would require addressing interleaving spurs in analog-to-digital converters (ADCs) through advanced ADC design or by implementing analog equalization techniques.
- Expanding transmission distance: Currently, the secure distance for this system is limited by excess noise, primarily attributed to laser phase noise. By optimizing modulation variance and employing advanced techniques like machine learning for carrier phase recovery, the transmission distance could be significantly extended.
- Full system integration: Although the current demonstration used bulk components on the transmitter side, integrating the transmitter would further enhance the technology’s readiness level and enable the creation of a complete transceiver for bi-directional communication.
This ground-breaking research signifies a major step towards making ultra-secure and high-speed quantum communication a practical reality. As the technology continues to evolve and improve, we can expect to see CV-QKD systems playing an increasingly important role in safeguarding our data and communications in the future.
Source
Continuous-variable quantum key distribution at 10 GBaud using an integrated photonic-electronic receiver
Published 21 August 2024