Based on a random interleaved optical pulse sequence consisting of wavelength-time quantum states, we have established a quantum lidar model. Multiple quantum states are used as a detection tool for the interception and interference of a target, and multiple wavelengths spanning the ultraviolet to near-infrared waveband are used to avoid interference and improve the detection efficiency. We elaborate upon the working principle of the entire quantum lidar detection system and demonstrate its feasibility through simulations, thereby establishing a foundation for the application of quantum lidar systems aboard satellite platforms at long distances from the high-precision detection of targets.
Based on a random interleaved optical pulse sequence consisting of wavelength-time quantum states, we have established a quantum lidar model. Multiple quantum states are used as a detection tool for the interception and interference of a target, and multiple wavelengths spanning the ultraviolet to near-infrared waveband are used to avoid interference and improve the detection efficiency. We elaborate upon the working principle of the entire quantum lidar detection system and demonstrate its feasibility through simulations, thereby establishing a foundation for the application of quantum lidar systems aboard satellite platforms at long distances from the high-precision detection of targets.
Quantum Lidar is a future technology that can mean different things to different people. To some it means detection and identification of classical-type lidar signals reflected from an illuminated target at or near the single photon level. This is facilitated by advances in semiconductor detector technology that allow highly efficient photocounting. To others it is more stringent, requiring exploitation of covertness associated with being essentially undetectable by the target in a thermal background, whilst allowing the lidar operator to filter her own signal from this noise. Again there is nothing specifically quantum about this. Any source that mimics of the energy rate per bandwidth seen by the illuminated object in the direction of the source can appear covert. In order to exploit quantum optics one can use inherent correlations, whether entangled or otherwise between light beams. Simple correlated optical beams can do this in two ways, perhaps by storing one beam as a reference and later performing correlated detection with the return signal in a phase sensitive manner. This is the “gold standard” for quantum lidar, but will be difficult outside of laboratory situations. In microscopy such phase control might be possible, or perhaps in the radio or microwave region for a quantum radar. Less challenging is a scenario in which an immediate local measurement of one beam conditions the beam sent to the target, allowing the return signal to be sifted from noise more easily. Here we will consider such a simple system, providing a range equation for a basic quantum lidar if it is to be operated covertly or openly. Open operation allows increased quantum signal brightness but also provides a quantum advantage, unspoofability – the lidar operator can in principle recognise their own return signal. We will also provide an analysis of quantum lidar detection based on quantum hypothesis testing and use this to perform Monte Carlo simulation of both target detections and false positive avoidance in a noisy background. The theory will be applied to experimental data.
Quantum light detection and ranging (LiDAR) utilizes quantum entanglement and correlation to improve precision, noise resilience and covertness of target detection. Despite recent advances, the development of a quantum LiDAR system that simultaneously achieves high precision and a large measurement range remains challenging. Here, we demonstrate a quantum amplitude-modulated continuous wave LiDAR with micrometer precision achievable via increased acquisition time and meter-scale measurement range. In our demonstration, the signal photons directly illuminate the target, while the idler photons are non-locally modulated with a high-frequency cosine wave and never interact with the target. By leveraging the non-local modulation and the quantum correlation, the target detection is achieved with a precision of 0.64 ± 0.06 mm within one second over a measurement range of 2-8 m. As the acquisition time is up to 500 s, the system achieves a precision of 29 ±4μm. Furthermore, our system realizes a 50 times precision improvement over the classical single-photon scheme in a background noise 37 dB stronger than the returned probe photons. With these advantages, our method will open venues for the development of high-precision, long-range, and noise-resilient target detection.
LiDAR systems that rely on classical signals are susceptible to intercept-and-recent spoofing attacks, where a target attempts to avoid detection. To address this vulnerability, we propose a quantum-secured LiDAR protocol that utilizes Gaussian modulated coherent states for both range determination and spoofing attack detection. By leveraging the Gaussian nature of the signals, the LiDAR system can accurately determine the range of the target through cross-correlation analysis. Additionally, by estimating the excess noise of the LiDAR system, the spoofing attack performed by the target can be detected, as it can introduce additional noise to the signals. We have developed a model for target ranging and security check, and conducted numerical simulations to evaluate the Receiver Operating Characteristic (ROC) of the LiDAR system. The results indicate that an intercept-and-recent spoofing attack can be detected with a high probability at a low false-alarm rate. Furthermore, the proposed method can be implemented using currently available technology, highlighting its feasibility and practicality in real-world applications.
Lidar (laser radar) offers advantages over conventional radar in terms of higher resolution, greater anti-interference capability and ultra-low altitude detection performance. However, Lidar has now reached a bottleneck in terms of detection range and is no longer able to correctly identify targets beyond 500 meters, thus failing to meet the requirements for detection, measurement and imaging. To break this bottleneck, we have developed a Quantum Lidar with a detection range of up to one kilometre, which is based on a quantum vacuum squeezed laser and can compress the photon fluctuation by 5.6dB in the vacuum state through quasi-phase matching in non-linear crystals, reducing the quantum noise of laser which accounts for 73% of the lidar, thus reducing the overall noise of the quantum lidar by 3.27dB and improves the phase stability of the laser (from 10 minutes to more than 120 minutes) to achieve higher accuracy measurements, with a Signal-Noise Ratio (SNR) twice that of conventional lidar, and therefore a sensitivity twice as high. The basic technical implementation is to use a 20W power 1064nm wavelength continuous wave laser (CW, M2 less than or equal to 1.05) to irradiate a target located one kilometre away. By detecting a very weak reflected laser (power=10μW ± 5μW) which is exponentially attenuated by distance, We use noiseless amplification by a quantum vacuum-squeezed laser with the same power magnitude to obtain a higher power (7dB amplification) and higher signal-noise ratio (4.77dB SNR improvement). A reflective lens set (250mm aperture) of our design is used to receive the laser diffusion due to the 4mrad transmission angle of one kilometre. In the squeezed laser system, the resonant cavity locking efficiency is improved to 99.7%, and the re-locking time is less than 0.3s, it is directly switchable with the balance homodyne detection system. The mode cleaner improves the transverse mode quality(the mode bandwidth is reduced by 67%) while filtering high-frequency noise. The quantum lidar imaging system has been developed, and the experimental results show that the resolution of the laboratory-simulated long-range decay experiment is 3 times higher than that of traditional lidar is a promising development. This means that the system can detect and image smaller objects and features with greater accuracy and precision. The use of a self-developed quantum enhancement algorithm to obtain a 5 times higher contrast lidar image is also a significant improvement, and the use of a quantum denoising algorithm to reduce graphic distortion and image scatter caused by atmospheric pollution and environmental interference is a critical development. These issues can significantly degrade the quality of lidar images, so being able to mitigate their effects is a significant step forward. Through a self-developed LiDAR 3D reconstruction algorithm, the reconstruction efficiency is increased by 3 times and the resolution is increased by 2.5 times, which means that the reconstructed 3D model is faster, more detailed and accurate. In the future, based on one kilometre's work, achieving a quantum lidar with a detection distance of 10, 20 or even 50 kilometres with much clearer images would require advancements by steadily improving the resolution, improving the signal-noise ratio of the system, improving the laser power and optimising the algorithm.
As a combination of laser technology and modern photoelectric detection technology, lidar (laser radar) has notable advantages compared with traditional radar such as high resolution, strong anti-interference ability, and good low-altitude detection performance. However, with continuous application in aerospace, military, artificial intelligence and other fields, lidar has reached the limits of classical physics and can’t meet the requirements in detection, measurement and imaging. In order to break the bottleneck, worldwide researchers have developed a new type of radar-quantum lidar, which is based on the combination of traditional radar technology and quantum information technology. Its main principle is to get imaging through squeezed light that is below the noise limit of classical physics and then manipulated by the quantum state to achieve imaging with higher quality. Quantum lidar in the paper injects quantum squeezed light to receiver end and uses quantum phase-sensitive amplifier technology to compensate the photon loss that caused by insufficient quantum power to further improve resolution. In the squeezed light, the generation of quantum squeezed light and detection theory are studied, the resonant cavity locking principle and balanced homodyne detection principle are analyzed, and a mode cleaner with narrow line width is designed to improve beam transverse mode quality of laser and filter high frequency noise. In order to reduce quantum noise and improve resolution, quantum lidar imaging system is developed and the theoretically derivation and numerical simulation results show that the resolution of quantum lidar imaging is 1.71 times higher than that of lidar imaging.
The challenges of optical interference and attacks are crucial in light detection and ranging (LiDAR) sensors. Random modulation of transmitted laser can effectively suppress interference and counter attacks. The robustness of LiDAR sensors to interference and attacks completely depends on the use of high-quality random numbers. Quantum random number generation (QRNG) provides an excellent solution for true random number generation due to the inherent probability properties of quantum processes. Using the built-in single-photon avalanche diode (SPAD) array of LiDAR to obtain random numbers has become an efficient QRNG solution. However, the current QRNG method only utilizes the temporal information of single-photon detection, resulting in low QRNG rates, especially under low light flux conditions. To this end, we propose a method to improve the QRNG rate, which generates quantum random numbers through pixel grouping in the spatial dimension and arrival time difference in the temporal dimension (GpDiff-QRNG). Experimental results indicate that the GpDiff-QRNG method significantly enhances the QRNG rate. In scenarios with a photon event probability of 1%, the QRNG rate of the GpDiff-QRNG method is 37 times higher than that of the traditional QRNG by difference of arrival time (Diff-QRNG) method. Furthermore, the random sequences generated by the GpDiff-QRNG method exhibit no periodicity and belong to pure random sequences of white noise. Our method greatly expands the application of QRNG for LiDAR anti-interference and anti-attack.