Experimental demonstration of Continuous-Variable Quantum Key Distribution with a silicon photonics integrated receiver

TL;DR

The paper demonstrates a continuous-variable QKD receiver implemented on a silicon photonics platform, enabling balanced detection and RF-heterodyne measurement with frequency-multiplexed pilots. By integrating the receiver on a CMOS-compatible chip and optimizing the amplification and DSP chain, the study reports an asymptotic secret-key rate of up to 2.4 Mbit/s at 10 km and 220 kbit/s at 23 km under laboratory conditions, illustrating the potential for fully integrated, high-speed metropolitan-secure communication. The work identifies current bottlenecks (packaging, electronics bandwidth, and coupling efficiency) and outlines concrete pathways toward scalable, chip-scale CV-QKD systems, including on-chip laser integration and enhanced packaging. Overall, the results provide a substantive proof-of-principle for silicon-photonics-based CV-QKD receivers and lay groundwork for practical, low-cost quantum-secure networks.

Abstract

Quantum Key Distribution (QKD) is a prominent application in the field of quantum cryptography providing information-theoretic security for secret key exchange. The implementation of QKD systems on photonic integrated circuits (PICs) can reduce the size and cost of such systems and facilitate their deployment in practical infrastructures. To this end, continuous-variable (CV) QKD systems are particularly well-suited as they do not require single-photon detectors, whose integration is presently challenging. Here we present a CV-QKD receiver based on a silicon PIC capable of performing balanced detection. We characterize its performance in a laboratory QKD setup using a frequency multiplexed pilot scheme with specifically designed data processing allowing for high modulation and secret key rates. The obtained excess noise values are compatible with asymptotic secret key rates of 2.4 Mbit/s and 220 kbit/s at an emulated distance of 10 km and 23 km, respectively. These results demonstrate the potential of this technology towards fully integrated devices suitable for high-speed, metropolitan-distance secure communication.

Figures (13)

• Figure 1: The CV-QKD Si PIC receiver platform. On the left, a picture of the platform. The photonic integrated chip (PIC) is wirebonded to the printed circuit board (PCB), which is itself on its power supply board. Optical coupling is done through a fiber array with two fibers on a 5-axis mechanical stage. The transimpedance and voltage amplifiers and the output of the device are also shown. On the right, the layout of the area of interest in the PIC and the associated schematic view, showing two grating couplers, one 50/50 beam splitter, two variable optical attenuators and two photodiodes. The chip hosts other photonic functions that are beyond the scope of this paper.
• Figure 2: I-V characteristics of the balanced photodetector. The curves correspond to the two photodiodes shown in Fig. \ref{['fig:receiver']} under dark and illumination conditions. To keep a low dark current and hence a low electronic noise, we choose a reverse bias of $0.5\,V$.
• Figure 3: Principle scheme of the amplification chain. The circuit is composed of a transimpedance amplifier followed by a non-inverting voltage amplifier. PD+ and PD- are the reverse bias voltages of the photodiodes. The power supply voltage filters and the 50 Ohms output DC filter are not shown.
• Figure 4: Noise performance comparison between PIC and bulk BHDs. The curves show a significant increase in the frequency bandwidth for an identical TIA between a solution with bulk photodiodes from Hamamatsu and a second with integrated photodiodes. In the second case, the parasitic capacitance at the input of the TIA is considerably reduced with respect to the test with bulk photodiodes due to wire bonding. In the working frequency range, the clearance has therefore been improved.
• Figure 5: Noise Power Spectral Densities (PSDs) for several input power levels. The power is given at the input of the receiver. The result for $P=0\,mW$ corresponds to the electronic noise.