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National Radio Science Conference

Faint-Pulse Single-Photon Source Triggered by FPGA

Mohamed Saleh, Salem F. Hegazy

Published May 6, 2025• 1 citation
Publisher

Abstract

Among various implementations of single-photon sources, faint-pulse single-photon sources provide a simple and practical approach based on attenuated coherent laser pulses. This work presents an experimental realization of a faint-pulse single-photon source using a 785-nm Grating Stabilized Laser Diode system, driven by a laser diode controller and modulated by a Field Programmable Gate Array (FPGA). The system's performance was evaluated by analyzing the photon detection rate as a function of pulse width and driving current. Results indicated a linear relationship between the single-photon detection rate and pulse width and an exponential dependence on driving current. The system achieved a photon emission probability of 10% per pulse, aligning with the requirements of practical quantum key distribution systems. This implementation demonstrates a cost-effective, scalable, and accessible platform for single-photon experiments, providing a foundation for future implementations of quantum communication protocols.

DOI
10.1109/nrsc65659.2025.11018579

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Among various implementations of single-photon sources, faint-pulse single-photon sources provide a simple and practical approach based on attenuated coherent laser pulses. This work presents an experimental realization of a faint-pulse single-photon source using a 785-nm Grating Stabilized Laser Diode system, driven by a laser diode controller and modulated by a Field Programmable Gate Array (FPGA). The system's performance was evaluated by analyzing the photon detection rate as a function of pulse width and driving current. Results indicated a linear relationship between the single-photon detection rate and pulse width and an exponential dependence on driving current. The system achieved a photon emission probability of 10% per pulse, aligning with the requirements of practical quantum key distribution systems. This implementation demonstrates a cost-effective, scalable, and accessible platform for single-photon experiments, providing a foundation for future implementations of quantum communication protocols.
Key distribution system using faint laser is very likely to become the first application exploiting the particular properties of single quanta called photons. In experimental key distribution system, it is highly demanded to use single-photon source for secure key distribution. Since there is not yet a laser source capable of producing such faint state, most experiments uses low coherent pulse laser, which is attenuated to produce a mean photon number mu. In this paper, we present an experimental setup to determine the mean photon number using a 300-ps low coherent pulse laser at 1550 nm for a practical crypto system. We will also present the effect of trigger frequency, detection efficiency and dark counts on average photon counts.
Single photon source is indispensable for realization of photon based quantum communication technologies such as quantum key distribution (QKD). Weak coherent pulse source is a practical, efficient and robust solution to generate stream of single photons, probabilistically. In this paper, a methodology for design and development of weak coherent pulse (WCP) source with high count rate of upto 10 Mcps is proposed and implemented. The generation of optical pulses with narrow pulse width and repetition rate of up to 100 MHz is achieved by developing a miniaturized pulse laser module. The weak coherent pulses are generated by heavily attenuating the laser pulses so as to reach the mean photon no. per pulse, μ, close to 0.1. WCP source performance in terms of mean photon number, second order coherence and photon count rate is also investigated. The measured g(2)[0] of ~0.98 shows that the developed WCP source has a very good quality.
The advent of quantum computers marks the beginning of the quantum 2.0 era. Unlike classical computers, quantum computers have faster and more efficient computational abilities, enabling them to break classical encryption such as the RSA (Rivest-Shamir-Adlemar) algorithm in a matter of minutes. To address this threat, a quantum communication system is required, which possesses quantum properties as well. The urgency of developing an independent and autonomous quantum communication system is crucial for a country. In this research, a transmitter for quantum communication based on faint pulse laser is developed. A weakened laser diode is used as the photon source. The laser diode weakening is achieved using a laser driver that generates short-duration pulse signals. By combining AND and XOR logic gates in such a way that when given a square wave input, the output of the logic gate system can produce short-duration pulses. The information in this communication system consists of randomly implemented keys, realized using the myRIO board and serving as a subsystem for random port selection. The designed laser driver produces pulse signals with a width of 128 nanoseconds and an amplitude of 1.5168 V. Additionally, the random port selection subsystem has been successfully designed using the myRIO board. Random numbers from ‘0’ to ‘3’ are generated uniformly. From 100 observation samples, an expected value of 1.445 and a variance of 0.911 are obtained. In the subsequent research, observations of single photon and the generated keys will be conducted.
In quantum cryptography, fundamental laws of quantum physics are exploited to enhance the security of cryptographic tasks. Quantum key distribution (QKD) is by far the most studied protocol to date, enabling the establishment of a secret key between trusted parties. Many practical use-cases in communication networks, however, involve parties who do not know or trust each other. The most fundamental quantum cryptographic building block in such a distrustful setting is quantum coin flipping, which has been studied only in few experimental studies to date using probabilistic quantum light sources facing fundamental limitations. Here, we experimentally implement a quantum strong coin flipping protocol using single-photon states and demonstrate an advantage compared to both classical realizations and implementations using faint laser pulses. We achieve this by employing a state-of-the-art deterministic single-photon source based on the Purcell-enhanced emission of a semiconductor quantum dot in combination with fast polarization-state encoding with sufficiently low quantum bit error ratio. The reduced multi-photon emission of the single-photon source yields a smaller bias of the coin flipping protocol compared to an attenuated laser implementation, both in simulations and in the experiment. By demonstrating a single-photon quantum advantage in a cryptographic primitive beyond QKD, our work represents a major advance towards the implementation of complex cryptographic tasks in a future quantum internet.
Quantum key distribution (QKD) offers a secure means of communication based on the laws of quantum physics. Despite its remarkable advancements, the current reliance of QKD on attenuated coherent (laser) light sources has imposed a fundamental limit on the secure key rate (SKR) per channel use. This constraint stems from the scarcity of single-photon components within coherent light, inherently bounded by a maximum of 1/e. Here, we report comprehensive demonstrations of single-photon-source-based high-rate QKD, surpassing the fundamental SKR limit imposed by the weak coherent light. By employing an on-demand, bright single-photon source with an efficiency of 0.71(2), coupled with narrow-bandwidth filtering and random polarization modulation, we demonstrated a field QKD trial over a 14.6(1.1) dB-loss free-space urban channel, achieving a SKR of 1.08×10^{-3} bits per pulse. This SKR surpasses the practical limit of weak coherent-light-based QKD by 79%. These findings unequivocally demonstrate the superior performance of single-photon sources over weak coherent light for QKD applications, marking a pivotal stride towards realizing a global quantum internet.
Faint laser pulses are practical signal sources in quantum key distribution. The photon statistics has been measured by recording every photo-counts moment and leading directly to the Mandel parameter of the photon distribution. Two different types operation of a single mode laser diode have been considered: either direct pulsing of the driving current or CW emission followed by pulse-shaping using an acousto-optic modulator. In both cases, it has been found that for practical attenuations, the photon distribution in each light pulse follows a poissonian statistics.