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Journal of Lightwave Technology

Polarization-Based Quantum Key Distribution Encoder and Decoder on Silicon Photonics

Gaolu Zhang, Zhizun Zhao, Jincheng Dai, Shanglin Yang, Xin Fu, Lin Yang

Published Nov 30, 2021• 29 citations
Publisher

Abstract

Private and secure communication is an indispensable part of the government and individual activities. With the ever-evolving large-scale of quantum computing, traditional public-key cryptography is severely threatened since its security only relies on the computational complexity of certain mathematical functions. Quantum key distribution (QKD), ascribed to its security based on the inviolability of physics laws, provides an absolutely information-secure solution for the future extensive communication encrypting. Herein this Letter, we proposed a simplified and reconfigurable silicon photonics encoder using a pass-block architecture and experimentally demonstrated its performance with a specialized silicon photonics decoder for high-speed quantum key distribution in polarization-based decoy-state BB84 protocol. We achieved an estimated asymptotic secret key rate of 868 kbps with measured quantum bit error rate (QBER) of 0.90% (Z base) and 1.34% (X base) over 20 km emulated fiber link. This work further advances the process of applying QKD using silicon photonics devices into the future secure telecommunication network.

DOI
10.1109/jlt.2021.3131193

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Private and secure communication is an indispensable part of the government and individual activities. With the ever-evolving large-scale of quantum computing, traditional public-key cryptography is severely threatened since its security only relies on the computational complexity of certain mathematical functions. Quantum key distribution (QKD), ascribed to its security based on the inviolability of physics laws, provides an absolutely information-secure solution for the future extensive communication encrypting. Herein this Letter, we proposed a simplified and reconfigurable silicon photonics encoder using a pass-block architecture and experimentally demonstrated its performance with a specialized silicon photonics decoder for high-speed quantum key distribution in polarization-based decoy-state BB84 protocol. We achieved an estimated asymptotic secret key rate of 868 kbps with measured quantum bit error rate (QBER) of 0.90% (Z base) and 1.34% (X base) over 20 km emulated fiber link. This work further advances the process of applying QKD using silicon photonics devices into the future secure telecommunication network.
Secure transmission of information is an indispensable part of the government and individual activities. Quantum key distribution (QKD), ascribed to its security based on the laws of quantum mechanics, has become an urgent research task to eliminate the rapidly growing threats of the ever-evolving large-scale quantum computing. In this Letter, we propose a silicon photonics transmitter using a pass-block architecture and experimentally demonstrated its performance with a demodulation chip for high-speed distributed-phase-reference QKD. We show estimated asymptotic secret key rates of 792 kbps for coherent-one-way protocol and 940 kbps for differential-phase-shift protocol over a 20 km emulated fiber link. This work provides new levels of flexibility, to the best of our knowledge, of using silicon photonics devices to incorporate QKD into future telecommunications networks.
Photonic integrated circuits provide a compact and stable platform for quantum photonics. Here we demonstrate a silicon photonics quantum key distribution (QKD) encoder in the first high-speed polarization-based QKD field tests. The systems reach composable secret key rates of 1.039 Mbps in a local test (on a 103.6-m fiber with a total emulated loss of 9.2 dB) and 157 kbps in an intercity metropolitan test (on a 43-km fiber with 16.4 dB loss). Our results represent the highest secret key generation rate for polarization-based QKD experiments at a standard telecom wavelength and demonstrate photonic integrated circuits as a promising, scalable resource for future formation of metropolitan quantum-secure communications networks.
Silicon-based polarization-encoding quantum key distribution (QKD) has been widely studied, owing to its low cost and robustness. However, prior studies have utilized off-chip devices to demodulate the quantum states or perform polarization compensation, given the difficulty of fabricating polarized independent components on the chip. In this paper, we propose a fully chip-based decoder for polarization-encoding QKD. The chip realizes a polarization state analyzer and compensates for the BB84 protocol without requiring additional hardware. It is based on a polarization-to-path conversion method that uses a polarization splitter-rotator. The chip was fabricated using a standard silicon photonics foundry; it has a compact design and is suitable for mass production. In the experimental stability test, an average quantum bit error rate of 0.56%0.56\%0.56% was achieved through continuous operation for 10 h without any polarization feedback. Furthermore, using the developed feedback algorithm, the chip enabled the automatic compensation of the fiber polarization drift, which was emulated by a random fiber polarization scrambler. In the case of the QKD demonstration, we obtained a finite-key secret rate of 240 bps over a fiber spool of 100 km. This study represents an important step toward the integrated, practical, and large-scale deployment of QKD systems.
Abstract Quantum communication has extremely high security and is a development direction of future communication networks. In this paper, an on-chip path, off-chip polarization encoded quantum key distribution (QKD) chip is designed and fabricated using advanced silicon photonics fabrication technology. Using a special two-dimensional grating, we can convert light of different path states into corresponding polarization states and propagate in fiber. The performance of the basic optics, waveguides, gratings, and Mach–Zehnder interferometers on the chip is characterized. In the demonstrated QKD experiment, the quantum bit error rate is as low as 1.08%. It provides an important device for the future development of advanced integrated quantum information.
The goal of cryptography is to encode data in such a way that no one can decode it unless they are the intended recipient. With the emergence of quantum computing, classical cryptography is not reliable enough to protect sensitive information. Nevertheless, there are alternatives. Quantum Key Distribution (QKD) is a method to secure communication based on the laws of quantum physics. Due to being impossible to measure the quantum state of a system without disturbing it, QKD provides a way to communicate between two parties while being, in theory, immune to eavesdropping. In this work, a free-space high-speed QKD setup is proposed, with the objective of implementing the polarization three-state one-decoy variant of the BB84 protocol. An assessment of the best type of laser diode to use for free-space QKD is made between several options. The system’s performance was assessed, incorporating a quantitative analysis of system losses and an estimation of the number of photons traversing the quantum channel. The system achieved a Quantum Bit Error Rate (QBER) of 1.58% for the Z basis and 1.46% for the X basis, for an average reception of two photons per pulse. Preliminary QBER measurements were also undertaken in the context of Quantum Keyless Private Communication protocols, focusing on the average number of photons per pulse.
Silicon (Si) photonics is reaching maturity and has the potential of offering low-cost, reliable, chip-scale systems for quantum key distribution (QKD). On the other hand, QKD is also maturing with the bridging of theory and practice. This work presents a Si integrated photonic transmitter for polarization-encoded QKD. The chip was fabricated in a standard Si photonic foundry process and integrates a pulse generator, intensity modulator, variable optical attenuator, and polarization modulator in a 1.3 mm x 3 mm die area. The devices in the photonic circuit meet the requirements for QKD. The transmitter was used in a proof-of-concept demonstration of the BB84 QKD protocol over a 5 km long fiber link. A quantum bit error rate of 5.4% and an asymptotic secure key rate of 0.95 kbps is obtained. This work shows the feasibility of foundry based Si photonics for quantum information applications.