應用非對稱位元率加碼與無絕熱干涉解碼穩定量子密鑰系統

Abstract

隨著量子計算與量子電腦的發展，傳統通訊所使用的加密方式將會在短時間內被破解。因此，迫切需要具備高安全性的量子密鑰分發(QKD)進行防範。在醫療，金融和軍事等重要應用領域已逐步開始應用。面對未來的資訊戰與訊息戰，量子通訊的重要性將與日俱增。 QKD訊號透過強度與相位調製器產生並由分佈回饋式雷射(DFBLD)作為載波。為了維持高傳輸穩定性的差分相移量子密鑰分發(DPS-QKD)傳輸，必須確保載波具有低雜訊(±0.227% of △P/P) ，低長期功率擾動(±0.02% of △P/P) ，低波長擾動(±0.5 pm)，以及低共振腔溫度擾動(±0.00105℃)和低偏置電流擾動(±5 μA) ，及較小的波長對電流和溫度的變化，分別為91.26 pm/℃ 和 1.31 pm/mA 。除此之外，296.6 kHz的窄線寬減少漏光所造成可見度下降。 此外，使用延遲1位元的延遲干涉儀(DLI)將相位鍵移(PSK)轉換為振幅鍵移(ASK)，ASK-流經由兩台單光子雪崩二極體(SPAD)透過比對來篩選正確的密鑰。透過縮短DLI的兩臂差，使延遲位元時間減少，提高DPS-QKD的傳輸頻率，並且減少可見度變化來自於波長擾動，線寬，電流擾動和環境溫度擾動所造成的影響，提升穩定性。然而，高傳輸率將造成與單光子偵測頻率有所差異，因此使用非對稱邊碼/解碼的方案實行，確保高FSR DLI可被使用和實現高穩定性傳輸。使用兩臂差為5公尺，1.04公尺和0.2公尺的DLI作為解調器，其對應傳輸頻率為40-MHz，192-MHz和1-GHz，在QKD傳輸1000碼時，量子誤碼率(QBER)為3.41×10^-2，2.56×10^-2和2.2×10^-2，安全密鑰速率(SKR)為22.457 kbit/s，60.084 kbit/s和77.318 kbit/s。 因為環境溫度會使光纖折射率與光纖長度產生變化，因此使用低密度/高密度聚苯乙烯(LDPS/HDPS) 作為絕熱材料來包覆DLI，使其降低溫度變化所造成可見度的擾動。當使用LDPS作為絕熱控制材料時，室溫下每小時擾動0.59℃/小時，穩定時間為2.31分鐘。在QKD傳輸1000碼時，QBER為4.12×10^-2，SKR為0。當使用HDPS作為絕熱材料時，室溫下每小時擾動僅0.07 ℃/小時，穩定時間為10.1分鐘。在QKD傳輸1000碼時，QBER為3.41×10^-2，SKR為22.457 kbit/s。因為傳輸距離增加，導致SPAD接收到光子數減少，SPAD的雜訊將逐漸影響QBER。最終，在傳輸65公里時，QBER為3.57×10^-2，SKR為1.3 kbit/s。實現長距離與長碼型的穩定QKD傳輸。

With the development of quantum computing and quantum computers, the encryption methods used in traditional communications will be cracked quickly. Therefore, a highly secure quantum key distribution is urgently needed for prevention. It has gradually begun to be used in essential application fields such as medical, financial, and military. In the face of future information and message wars, the importance of quantum communications will increase daily. The QKD signal is generated through intensity and phase modulators and uses a distributed feedback DFBLD (DFBLD) as a carrier. In order to maintain high transmission stability for differential phase-shift quantum key distribution (DPS-QKD) transmission, it is necessary to ensure that the carrier has low noise (±0.227% of△P/P) and low long-term power disturbance (±0.02% of△P/P), low wavelength perturbation (±0.5 pm), as well as low resonant cavity temperature perturbation (±0.00105℃) and low bias current perturbation (±5 μA), and smaller wavelength changes to current and temperature, respectively are 91.26 pm/℃ and 1.31 pm/mA. In addition, the narrow linewidth of 296.6 kHz reduces visibility loss caused by light leakage. In addition, a delay interferometer (DLI) with a delay of 1 bit is used to convert the phase shift key (PSK) into an amplitude shift key (ASK). The ASK streams pass through two single-photon avalanche diodes (SPAD) to select the correct key through comparison. By shortening the difference between the two arms of DLI, the 1-bit delay time is reduced, the transmission frequency of DPS-QKD is increased, and the impact of visibility changes caused by wavelength disturbance, linewidth, current disturbance, and environmental temperature disturbance is reduced, improving stability. However, the high transmission rate will cause a difference from the single photon detection frequency, so an asymmetric encode/decoding scheme is used to ensure high transmission stability with high FSR DLI. Using DLI with two arm differences of 5 meters, 1.04 meters, and 0.2 meters as a demodulator, the corresponding transmission frequencies are 40-MHz, 192-MHz, and 1-GHz. When QKD transmits 1000 codes, the quantum error rate (QBER) is 3.41×10^-2, 2.56×10^-2 and 2.2×10^-2, and the security key rate (SKR) is 22.457 kbit/s, 60.084 kbit/s and 77.318 kbit/s. Because the environmental temperature will change the fiber's refractive index and fiber length, low-density/high-density polystyrene (LDPS/HDPS) is used as an insulating material to cover the DLI and reduce the visibility disturbance caused by temperature fluctuations. When using LDPS as the thermal insulation control material, the per-hour disturbance at room temperature is 0.59°C/hour, and the stabilization time is 2.31 minutes. When QKD transmits 1000 codes, QBER is 4.12×10^-2 and SKR is 0. When HDPS is used as the thermal insulation material, the hourly disturbance at room temperature is only 0.07 °C/hour, and the stabilization time is 10.1 minutes. When QKD transmits 1000 codes, QBER is 3.41×10^-2, and SKR is 22.457 kbit/s. As the transmission distance increases, the number of photons received by SPAD decreases, and the noise of SPAD will gradually affect QBER. Finally, when transmitting 65 kilometers, the QBER is 3.57×10^-2, and the SKR is 1.3 kbit/s. Achieve stable QKD transmission over long distances and long code patterns.