Integrated Quantum Rangefinding

Rangefinding is a task in metrology that aims to determine the distance between an observer and an object of interest. Often this goal is achieved by direct time-of-flight measurements, where subsequent pulses of electromagnetic radiation are sent towards the object. When this radiation returns to the sender, the time that has passed since the radiation was sent out is measured. Together with the speed of light through the atmosphere, this time can be used to calculate the distance between the object and the observer. This principle is most famously used in radar and lidar, where electro-magnetic radiation in the microwave and optical band is used, respectively. Rangefinding has many practical applications in civil engineering, construction and law enforcement but also in the defense sector. State-of-the-art rangefinders use bright light to illuminate the object of interest, which makes the sender very easy to detect. Similar to when we are using a torch in a dark night where the flare of our torch can be much easier spotted than we can spot another person not holding a torch. Our project, inspired by quantum illumination, aims to replace this bright light with quantum light. For this purpose, we build on our previous work in spontaneous parametric down -conversion in aluminum gallium arsenide waveguides. The light produced in a down-conversion process is not only much fainter than the typically used laser sources but, all importantly, its quantum properties perfectly protect the light against detection by any other party than the sender. The projects goal is to implement this covert approach to rangefinding in an integrated way using our on-chip down-conversion sources.

Rangefinding is a task in metrology that aims to determine the distance between an observer and an object of interest. Often this goal is achieved by direct time-of-flight measurements, where subsequent pulses of electromagnetic radiation are sent towards the object. When this radiation returns to the sender, the time that has passed since the radiation was sent out is measured. Together with the speed of light through the atmosphere, this time can be used to calculate the distance between the object and the observer. This principle is most famously used in radar and lidar, where electro-magnetic radiation in the microwave and optical band is used, respectively. Rangefinding has many practical applications in civil engineering, construction and law enforcement but also in the defense sector. State-of-the-art rangefinders use bright light to illuminate the object of interest, which makes the sender very easy to detect. Similar to when we are using a torch in a dark night where the flare of our torch can be much easier spotted than we can spot another person not holding a torch. Our project, inspired by quantum illumination, aimed to replace this bright light with quantum light. For this purpose, we built on our previous work in spontaneous parametric down-conversion in aluminum gallium arsenide waveguides. The light produced in a down-conversion process is not only much fainter than the typically used laser sources but, all importantly, its quantum properties perfectly protect the light against detection by any other party than the sender. In the project's we successfully demonstrated this approach to rangefinding with high levels of accuracy and covertness. The results were published in a number of articles and presented at many conferences. This protocol and these sources can be developed further towards real-world applications.