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Journal of Instrumentation

A laser light source control system for continuous variable quantum key distribution

S.J. Zhang, H. Liang

Published May 5, 2020• 3 citations
Publisher

Abstract

Compared with discrete variable quantum key distribution, continuous variable quantum key distribution (CVQKD) has the advantages of low cost, good stability, and high channel capacity, in addition to unconditional security and detectability for wiretapping. The basis of CVQKD system operation is the realization of loading information into photon quantum states. In this paper, a laser light source control system has realized the control and adjustment of the photon quantum states and completed the encoding of quantum states. In order to generate synchronous optical signals, FPGA, multi-channel DAC and micro power ADC are used to control the source of the synchronous optical laser. The control and modulation of multiple optical components are realized based on FPGA, multiple 16-bit 1.0 GSPS DACs and high-performance operational amplifiers. The electronic test results show that the system implements the control and adjustment functions of lasers, amplitude modulator, phase modulators, variable optical attenuators, polarization controllers, as well as detection of synchronized light. The performance of the laser light source control system fully meets the requirements of the CVQKD system.

DOI
10.1088/1748-0221/15/05/p05003

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Compared with discrete variable quantum key distribution, continuous variable quantum key distribution (CVQKD) has the advantages of low cost, good stability, and high channel capacity, in addition to unconditional security and detectability for wiretapping. The basis of CVQKD system operation is the realization of loading information into photon quantum states. In this paper, a laser light source control system has realized the control and adjustment of the photon quantum states and completed the encoding of quantum states. In order to generate synchronous optical signals, FPGA, multi-channel DAC and micro power ADC are used to control the source of the synchronous optical laser. The control and modulation of multiple optical components are realized based on FPGA, multiple 16-bit 1.0 GSPS DACs and high-performance operational amplifiers. The electronic test results show that the system implements the control and adjustment functions of lasers, amplitude modulator, phase modulators, variable optical attenuators, polarization controllers, as well as detection of synchronized light. The performance of the laser light source control system fully meets the requirements of the CVQKD system.
Compared with discrete variable quantum key distribution, the Continuous Variable Quantum Key Distribution (CVQKD) system has the advantages of simple equipment, low technical difficulty, and high channel capacity, in addition to unconditional security and detectability for wiretapping. In this paper, the laser light source control system realizes the control and adjustment functions of the photon quantum state, which was encoded with information. In order to generate the synchronous optical pulse signals, the Field Programmable Gate Array (FPGA), multi-channel Digital to Analog Converter (DAC), and micro power Analog to Digital Converter (ADC) were used to control the synchronous optical laser. The control of multiple amplitude modulators and phase modulators is achieved based on the FPGA and high-speed DAC. At present, the electronics performance test of the laser light source control system has been completed, and the results show that the requirements of the CVQKD system index are met.
The Continuous-variable quantum key distribution (CVQKD) technique is one of the practical uses of quantum information technology. CVQKD system is implemented based on existing optical networks and standard telecommunication technologies. CVQKD can be put into use of the information transmission in city-based areas, within the extent of absolute security and without any restrictions of security. To reduce the experimental system to a commercial prototype, a data acquisition (DAQ) card can be used to replace the DAQ equipment in the laboratory. It can save the cost of the system experiment and commercial application. In this paper, through the high-speed DAQ card, we implement the collection and uploading of the electrical signal, when the light passes through the continuous optical coherent state detector. The whole experiment test system consists of a field-programmable gate array (FPGA), an analog-to-digital converter (ADC) chip, and optical components. This paper provides a method of gain adjustment of the balanced homodyne detector and a way to test the π phase voltage of the optical modulator. The results show that the DAQ card can be used in the development of the CVQKD prototype.
Continuous variable quantum key distribution (CVQKD) uses the continuous quadratures of light to share a secret key between a transmitter and receiver. The presence of an eavesdropper can be detected by fundamental quantum mechanics. Compared to the more established discrete variable QKD, CVQKD uses more cost-effective homodyne detectors which are more compatible with current telecommunication technologies. In a future global quantum network, CVQKD could be used to ensure the secure exchange of information. In this work, the feasibility of a variety of CVQKD protocols in different channels that could be used to establish a global quantum network are studied. These are the Gaussian modulated and discrete modulated CVQKD protocols for satellite to optical ground station downlinks and uplinks for Earth-space connections, inter-satellite links for space connections, satellite to ship and underwater links for maritime connections, and fibre network links for terrestrial connections. Secret key distribution between continents and various regions is simulated while accounting for the different adverse effects associated with each link. The combination of these connections with routing and scheduling ensures inter-continental high-speed information exchange with unconditional security that is required to achieve the goal of a global quantum network.
Integrated quantum key distribution (QKD) systems based on photonic chips have high scalability and stability, and are promising for further construction of global quantum communications networks. On-chip quantum light sources are a critical component of a fully integrated QKD system; especially a continuous-variable QKD (CV-QKD) system based on coherent detection, which has extremely high requirements for the light sources. Here, for what we believe is the first time, we designed and fabricated two on-chip tunable lasers for CV-QKD, and demonstrated a high-performance system based on these sources. Because of the high output power, fine tunability, and narrow linewidth, the involved on-chip lasers guarantee the accurate shot-noise-limited detection of quantum signals, center wavelength alignment of nonhomologous lasers, and suppression of untrusted excess noise. The system’s secret key rate can reach 0.75 Mb/s at a 50 km fiber distance, and the secure transmission distance can exceed 100 km. Our results mark a breakthrough toward building a fully integrated CV-QKD, and pave the way for a reliable and efficient terrestrial quantum-secure metropolitan area network.
In a practical continuous variable quantum key distribution (CVQKD) system, frame synchronization is crucial for its operation, especially in conditions of low signal-to-noise ratio (SNR) and phase drift. This paper introduces a robust frame synchronization scheme for CVQKD systems that only utilizes quantum signals. The proposed scheme effectively employs randomly selected segments of quantum signals to achieve frame synchronization, eliminating the need for additional modulation. The performance of this scheme applied in a local local oscillator scenario is thoroughly analyzed through numerical simulations. The results demonstrate that the proposed scheme is capable of withstanding low SNR and arbitrary slow phase drift, as well as fast phase drift originates from two independent lasers, while also slightly improving the secret key rate compared to the scheme using inserted synchronization frames. These findings validate the feasibility of implementing the proposed scheme for long-distance CVQKD in practical scenarios.
In practical quantum communication networks, the scheme of continuous-variable quantum key distribution (CVQKD) faces a challenge that the entangled source is controlled by a malicious eavesdropper, and although it still can generate a positive key rate and security, its performance needs to be improved, especially in secret key rate and maximum transmission distance. In this paper, we proposed a method based on the four-state discrete modulation and a heralded hybrid linear amplifier to enhance the performance of CVQKD where the entangled source originates from malicious eavesdropper. The four-state CVQKD encodes information by nonorthogonal coherent states in phase space. It has better transmission distance than Gaussian modulation counterpart, especially at low signal-to-noise ratio (SNR). Moreover, the hybrid linear amplifier concatenates a deterministic linear amplifier (DLA) and a noiseless linear amplifier (NLA), which can improve the probability of amplification success and reduce the noise penalty caused by the measurement. Furthermore, the hybrid linear amplifier can raise the SNR of CVQKD and tune between two types of performance for high-gain mode and high noise-reduction mode, therefore it can extend the maximal transmission distance while the entangled source is untrusted.