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Computación y Sistemas

FPGA-Based Emulation of a Synchronous Phase-Coded Quantum Cryptography System

Josué Aarón López-Leyva, Jorge Luis Ureña Castro, L. Sanchez, F.J Mendieta Jimenez, Arturo Arvizu‐Mondragón

Published Mar 31, 2015• 2 citations
Publisher

Abstract

We present FPGA-based emulation of a synchronous phase-coded quantum cryptography system. Several of the emulated subsystems are used for implementation in a free space demonstrative QPSK scheme for quantum key distribution with continuous variables (CV-QKD) using a base and optical phase synchronization. The CV-QKD systems are commonly implemented using QPSK modulation with switched or simultaneous detection. In this paper we only make use of one base of the QPSK system in order to get a simpler modulation (BPSK) scheme, used for demonstrative purposes. The reported results from the emulation and the experiment in terms of Quantum Bit Error Rate (QBER) and mutual information for different values of the number of photons per bit are in good agreement.

DOI
10.13053/cys-19-1-1549

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We present FPGA-based emulation of a synchronous phase-coded quantum cryptography system. Several of the emulated subsystems are used for implementation in a free space demonstrative QPSK scheme for quantum key distribution with continuous variables (CV-QKD) using a base and optical phase synchronization. The CV-QKD systems are commonly implemented using QPSK modulation with switched or simultaneous detection. In this paper we only make use of one base of the QPSK system in order to get a simpler modulation (BPSK) scheme, used for demonstrative purposes. The reported results from the emulation and the experiment in terms of Quantum Bit Error Rate (QBER) and mutual information for different values of the number of photons per bit are in good agreement.
Quantum key distribution (QKD) is the most matured application of quantum communication. The time synchronization and system timing jitter are essential to a practical QKD experiment, which can directly influence the quantum bit error rate (QBER) and the final key rate. High precision time-to-digital converters (TDCs) can effectively reduce the system timing jitter, resulting in lower QBER and higher key rate. Here, we introduce a TDC based on a field programmable gate array (FPGA). Its high resolution (LSB) of 50 ps with precision (RMS) less than 50 ps, low dead time and large dynamic range can well meet the requirement of the QKD experiment. A free space QKD system setup using the FPGA-based TDC has been assembled. The timing precision of the synchronous light and the system timing jitter were determined. The results demonstrate that the FPGA-based TDC could be successfully applied in the QKD experiment.
This paper proposes to design a satellite-based free-space quantum key distribution (QKD) systems using quadrature phase-shift-keying (QPSK) signaling. Our proposed QKD system based on continuous variable encoding to provide the secret-key transmission, where the key information is encoded on four coherent states corresponding to QPSK modulation scheme. In addition, we use heterodyne detection receiver to improve the receiver sensitivity thus decode the signal with high fidelity. The performance of the proposed free-space QKD system is analytically investigated. More especially, the mathematical expression for quantum bit error rate (QBER) is derived taking into account the effect of physical layer impairments and parameters. The numerical results help to determine the appropriate values of system's parameters such as the threshold coefficients and the required transmitted power.
Quantum key distribution (QKD) provides a secure and effective way of exchanging cryptographic symmetric keys without the possibility of an eavesdropper being undetected. The transmission and detection of the quantum states at the physical layer is the first step to defining a common source of entropy, where both parties will extract a raw key. Over the last few years, continuous variable quantum key distribution (CV-QKD) protocols have become an attractive technology for QKD, providing a low-cost solution that can be easily integrated with the current optical network devices and infrastructure. Unlike other QKD technologies, a CV protocol requires complex and highly computationally demanding digital signal processing (DSP) operations. In that sense, parallel computation tools such as field programmable gate arrays (FPGAs) represent a key element for the practical implementation of this quantum technology and to scale its performance in terms of distance and secret key rate indicators. This work presents an FPGA-based implementation of the physical layer of a CV-QKD transmitter. The proposed architecture and employed protocols are described, and hardware implementation aspects are discussed, including resource occupation analysis, configuration parameters, and timing issues.
Abstract Continuous variable quantum key distribution (CV-QKD) is a promising emerging technology for the distribution of secure keys for symmetric encryption. It can be readily implemented using commercial off-the-shelf optical telecommunications components. A key requirement of the CV-QKD receiver is the ability to measure the quantum states at the correct time instance and rate using the correct orthogonal observables, referred to as synchronization. We propose a digital synchronization procedure for a modern CV-QKD system with locally generated local oscillator for coherent reception. Our proposed method is modulation format independent allowing it to be used in a variety of CV-QKD systems. We experimentally investigate its performance with a Gaussian modulated CV-QKD system operating over a 10–20 km span of standard single mode fibre. Since the procedure does not require hardware modifications it paves the way for cost-effective QKD solutions that can adapt rapidly to changing environmental conditions.
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.
Quantum key distribution (QKD) is the most matured application of quantum communication. The time synchronization and system timing jitter are essential to a practical QKD experiment, which can directly influence the quantum bit error rate (QBER) and the final key rate. High precision time-to-digital convertor (TDC) can effectively reduce the system timing jitter, resulting in lower QBER and higher key rate. Here, we introduce a TDC based on a field-programmable gate array (FPGA). Its high resolution of 50 ps, low dead time and large dynamic range can well meet the requirement of the QKD experiment. A free space QKD system setup using the FPGA-based TDC has been built up. The timing precision of the synchronous light and the system timing jitter were tested. The results demonstrate that the FPGA-based TDC could be successfully applied in the QKD experiment.