Influence of Source Parameters on the Polarization Properties of Beams for Practical Free-Space Quantum Key Distribution

Polarization encoding has been extensively used in quantum key distribution (QKD) implementations along free-space links. However, the calculation model to characterize channel transmittance and quantum bit error rate (QBER) for free-space QKD has not been systematically studied. As a result, it is often assumed that misalignment error is equal to a fixed value, which is not theoretically rigorous. In this paper, we investigate the depolarization and rotation of the signal beams resulting from spatially-dependent polarization effects of the use of curved optics in an off-axis configuration, where decoherence can be characterized by the Huygens–Fresnel principle and the cross-spectral density matrix (CSDM). The transmittance and misalignment error in a practical free-space QKD can thus be estimated using the method. Furthermore, the numerical simulations clearly show that the polarization effect caused by turbulence can be effectively mitigated when maintaining good beam coherence properties.

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Full daylight quantum-key-distribution at 1550 nm enabled by integrated silicon photonics

npj Quantum Information ◽

10.1038/s41534-021-00421-2 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

M. Avesani ◽

L. Calderaro ◽

M. Schiavon ◽

A. Stanco ◽

C. Agnesi ◽

...

Keyword(s):

Optical Fibers ◽

Silicon Photonics ◽

Free Space ◽

Quantum Key Distribution ◽

Cost Effective ◽

Key Distribution ◽

Global Scale ◽

Secret Key ◽

Quantum Bit ◽

Integrated Silicon Photonics

AbstractThe future envisaged global-scale quantum-communication network will comprise various nodes interconnected via optical fibers or free-space channels, depending on the link distance. The free-space segment of such a network should guarantee certain key requirements, such as daytime operation and the compatibility with the complementary telecom-based fiber infrastructure. In addition, space-to-ground links will require the capability of designing light and compact quantum devices to be placed in orbit. For these reasons, investigating available solutions matching all the above requirements is still necessary. Here we present a full prototype for daylight quantum key distribution at 1550 nm exploiting an integrated silicon-photonics chip as state encoder. We tested our prototype in the urban area of Padua (Italy) over a 145 m-long free-space link, obtaining a quantum bit error rate around 0.5% and an averaged secret key rate of 30 kbps during a whole sunny day (from 11:00 to 20:00). The developed chip represents a cost-effective solution for portable free-space transmitters and a promising resource to design quantum optical payloads for future satellite missions.

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HỆ THỐNG PHÂN PHỐI KHÓA LƯỢNG TỬ ĐA KÊNH TỪ VỆ TINH SỬ DỤNG SCM-WDM

Journal of Military Science and Technology ◽

10.54939/1859-1043.j.mst.72.2021.35-43 ◽

2021 ◽

pp. 35-43

Author(s):

Hiền

Keyword(s):

Wavelength Division Multiplexing ◽

Bit Error Rate ◽

Error Rate ◽

Free Space ◽

Quantum Key Distribution ◽

Key Distribution ◽

Secret Key ◽

Quantum Bit ◽

Wavelength Division ◽

Free Space Optic

Phân phối khoá lượng tử QKD (Quantum Key Distribution) là giải pháp có khả năng đảm an ninh vô điều kiện nhờ áp dụng luật cơ lượng tử để phân phối khóa an toàn giữa hai bên hợp pháp với sự hiện diện của kẻ nghe lén. Sử dụng vệ tinh để phân phối khóa lượng tử tới các trạm mặt đất qua kênh quang không gian tự do FSO (Free Space Optic) là giải pháp hứa hẹn tạo ra một mạng QKD phạm vi toàn cầu. Tuy nhiên, do ảnh hưởng của kênh FSO, đặc biệt là nhiễu loạn khí quyển, tốc độ truyền khóa bí mật SKR (Secret Key Rate) của các hệ thống QKD hiện tại bị hạn chế. Do đó, nghiên cứu này đề xuất mô hình hệ thống QKD đa kênh dựa trên ghép kênh phân chia theo bước sóng WDM (Wavelength Division Multiplexing) và ghép kênh sóng mang phụ SCM (Sub Carrier Multiplexing) nhằm tăng SKR. Sử dụng phương pháp phân tích lý thuyết với các công cụ giải tích và xác suất, nhóm tác giả đã xây dựng các công thức tính toán SKR và tỉ lệ lỗi bit lượng tử của hệ thống đề xuất. Kết quả khảo sát hiệu năng cho thấy, hệ thống QKD đa kênh cho phép cải thiện SKR so với hệ thống đơn kênh trong khi vẫn đảm bảo yêu cầu về QBER (Quantum Bit Error Rate).

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Modeling and Simulation for Performance Evaluation of Optical Quantum Channels in Quantum key Distribution Systems

Al-Khwarizmi Engineering Journal ◽

10.22153/kej.2021.05.001 ◽

2021 ◽

Vol 17 (2) ◽

pp. 31-44

Author(s):

Adil Fadhil Mushatet ◽

Shelan Khasro Tawfeeq

Keyword(s):

Performance Evaluation ◽

Optical Fiber ◽

Free Space ◽

Quantum Channel ◽

Quantum Key Distribution ◽

Distribution Systems ◽

Key Distribution ◽

Quantum Channels ◽

Quantum Bit ◽

Modeling Process

In this research work, a simulator with time-domain visualizers and configurable parameters using a continuous time simulation approach with Matlab R2019a is presented for modeling and investigating the performance of optical fiber and free-space quantum channels as a part of a generic quantum key distribution system simulator. The modeled optical fiber quantum channel is characterized with a maximum allowable distance of 150 km with 0.2 dB/km at =1550nm. While, at =900nm and =830nm the attenuation values are 2 dB/km and 3 dB/km respectively. The modeled free space quantum channel is characterized at 0.1 dB/km at =860 nm with maximum allowable distance of 150 km also. The simulator was investigated in terms of the execution of the BB84 protocol based on polarizing encoding with consideration of the optical fiber and free-space quantum channel imperfections and losses by estimating the quantum bit error rate and final secure key. This work shows a general repeatable modeling process for significant performance evaluation. The most remarkable result that emerged from the simulated data generated and detected is that the modeling process provides guidance for optical quantum channels design and characterization for other quantum key distribution protocols.

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Geometrical Optics Restricted Eavesdropping Analysis of Satellite-to-Satellite Secret Key Distillation

Entropy ◽

10.3390/e23080950 ◽

2021 ◽

Vol 23 (8) ◽

pp. 950

Author(s):

Ziwen Pan ◽

Ivan B. Djordjevic

Keyword(s):

Free Space ◽

Quantum Key Distribution ◽

Security Analysis ◽

Key Distribution ◽

Geometrical Optics ◽

Secret Key ◽

Satellite Applications

Traditionally, the study of quantum key distribution (QKD) assumes an omnipotent eavesdropper that is only limited by the laws of physics. However, this is not the case for specific application scenarios such as the QKD over a free-space link. In this invited paper, we introduce the geometrical optics restricted eavesdropping model for secret key distillation security analysis and apply to a few scenarios common in satellite-to-satellite applications.

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