In Quantum Key Distribution (QKD), the time tagging (with a synchronized timing reference) of photon transmission/reception events is of utmost importance for the purposes of coincidence identification to obtain the sifted key between the communicating terminals (A: Aryabhata and B: Bhaskara). In entangled photon based QKD system, both communicating terminals receive the photons whereas in case of weak coherent photon based QKD system, one terminal transmits the photons, which are received at receiver. For the coincidence identification in QKD system, it is necessary to synchronize the time bases used for time tagging of photons between the communicating terminals operating at independent clocks. This paper presents timing synchronization and FPGA implementation of Time of Flight (ToF) estimation in a NavIC synchronized real time Quantum Key Distribution (QKD) system. The proposed time synchronization and Time of Flight estimation method has been implemented and successfully used in ISRO’s and India’s first successful demonstration of 300m free space entangled photon based real time quantum key distribution system and weak coherent photon based real time QKD system as well. The achieved accuracy for time of flight estimation is 10ns and timing synchronization within 20ns.
In Quantum Key Distribution (QKD), the time tagging (with a synchronized timing reference) of photon transmission/reception events is of utmost importance for the purposes of coincidence identification to obtain the sifted key between the communicating terminals (A: Aryabhata and B: Bhaskara). In entangled photon based QKD system, both communicating terminals receive the photons whereas in case of weak coherent photon based QKD system, one terminal transmits the photons, which are received at receiver. For the coincidence identification in QKD system, it is necessary to synchronize the time bases used for time tagging of photons between the communicating terminals operating at independent clocks. This paper presents timing synchronization and FPGA implementation of Time of Flight (ToF) estimation in a NavIC synchronized real time Quantum Key Distribution (QKD) system. The proposed time synchronization and Time of Flight estimation method has been implemented and successfully used in ISRO’s and India’s first successful demonstration of 300m free space entangled photon based real time quantum key distribution system and weak coherent photon based real time QKD system as well. The achieved accuracy for time of flight estimation is 10ns and timing synchronization within 20ns.
A light synchronization scheme to solve the key problem of signal synchronization in quantum key distribution(QKD)system is proposed.At side of the transmitter,the field-programmable gate array (FPGA)chip produces a synchronization pulse sequence of certain pattern.The pulse sequence drives laser to transmit sync light through one fiber along with signal light to the receiver.The sync light reverts to sync pulse sequence through fast discrimination at side of the receiver,and the pulses are provided to the single-photon detector as gate after high-precision delay adjustment.Simultaneously,the receiver uses a high-frequency clock to sample the sync pulse sequence in FPGA for encoding,synchronizing the transmitter and receiver.The scheme has a high-precision,low-cost,high fault tolerance feature,and was successfully applied to metro quantum communication network.
In this paper, we present a real-time Quantum Key Distribution (QKD) implementation on Field Programmable Gate Arrays (FPGAs) for secure communication. We propose a novel methodology with a Python-based programming interface for rapid development on FPGA. Our methodology revolves three phases of development. In the first phase, a reference model of an entangled photon source and the proposed QKD system are developed in Python. Next, the reference model is passed through a thorough verification phase. In the second phase, the reference model is implemented on the Processing System (PS) part of the FPGA. Finally in the third phase, the computationally intensive part of the QKD architecture is off-loaded on to the Programmable Logic (PL) part of the FPGA for acceleration. We employ PYNQ framework in our QKD development and successfully combine the convenience of Python productivity with FPGA based acceleration.
Unmanned Aerial Vehicles (UAVs) are used in numerous applications ranging from defense, law enforcement, environmental monitoring, disaster recovery, aerial photography, and delivering consumer packages. Securing wireless communication between drones in-flight is critical to ensure safe operation during flight and avoid multiple types of attacks, e.g., eavesdropping, spoofing, jamming, etc. Quantum communication protocols offer enhancements over classical approaches. In this effort, we present progress towards demonstrating Quantum Key Distribution (QKD) between two drones in flight. A significant challenge includes achieving system performance using compact Size, Weight, and Power (SWaP) constraints of the drone vehicle. We introduce and evaluate critical subsystems including the QKD source, which is based on resonant-cavity Light Emitting Diodes (LED) controlled by an FPGA, and we discuss a secondary QKD source based on a fiber-coupled polarization modulator. The Pointing, Acquisition and Tracking (PAT) system is comprised of several cascading subsystems, which provide course alignment using based on Infrared (IR) beacons/cameras with gimbals, and fine alignment using Fast Steering Mirrors (FSM) with absolute encoders and feedback position sensors. We discuss both transmit and receive optics including custom designed 3D-printed optical benches. Finally, we introduce single-photon detectors, FPGA-based time-tagger, and a novel statistical post-processing synchronization algorithm. Establishing a quantum communications link between drones in-flight is an important prerequisite for future drone-based quantum applications such as entanglement distribution, distributed quantum sensing, and Quantum Positional Verification (QPV).
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.
A real-time quantum key distribution (QKD) system is developed in this paper. In the system, based on the feature of a field-programmable gate array, secure key extraction control and algorithm have been optimally designed to perform sifting, error correction, and privacy amplification altogether in real time. In the QKD experiment, information synchronization mechanism and high-speed classic data channel are designed to ensure the steady operation of the system. Decoy state and synchronous laser light source are used in the system, while the length of optical fiber between Alice and Bob is 20 km. With photons repetition frequency of 20 MHz, the final key rate could reach 17 kb/s. Smooth and robust operation is verified with 6 h continuous test and associated with encrypted voice communication test.
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.