Atomic Photodetector Detects Photon-level Signals in Sunlight at Rates of Order Photons/s

Detecting faint signals of single photons against the overwhelming glare of sunlight presents a formidable challenge for modern sensing technologies. Laura Zarraoa, Romain Veyron, Tomas Lamich, and colleagues at ICFO, The Barcelona Institute of Science and Technology, and ICREA, have now demonstrated a novel approach to this problem, successfully detecting individual photon arrivals even when embedded within the intense background of sunlight. Their work centres on a ‘jump photodetector’, utilising a single trapped rubidium atom to act as an exceptionally sensitive and narrow-band light sensor. This achievement represents a significant step forward for applications requiring detection in bright light, potentially revolutionising areas such as daytime LIDAR, remote sensing, and free-space optical communications by overcoming limitations imposed by background noise.

Single-Atom Control and Quantum Memory Potential

Researchers are pioneering a new approach to detecting extremely faint light signals by harnessing the unique properties of individual rubidium atoms. This technique, termed a “jump photodetector”, overcomes the significant challenge of distinguishing weak signals from intense background light, such as sunlight, by utilizing the atom’s internal state as a highly selective filter. The team traps a single rubidium atom and precisely monitors its transitions between energy levels when exposed to incoming photons, effectively creating a narrowband detector. To demonstrate the capabilities of this technique, scientists embedded weak laser photons within intense sunlight, simulating a challenging real-world scenario.

They developed a detailed model to accurately describe the atom’s behaviour under these conditions, confirming strong agreement between theoretical predictions and experimental results. This model enabled precise calculation of the system’s capacity to transmit information under noisy conditions, achieving a rate of 0. 5 bits per symbol with a relatively weak signal of 150 photons over a 10 millisecond period. Experiments achieved a data rate of 0. 5 bits per symbol when transmitting 150 probe photons over a 10 millisecond interval, all while the system was illuminated by 1 nanowatt of sunlight. This demonstrates the ability to reliably detect individual photons even in the presence of overwhelming background noise, promising applications in areas like daytime light detection and ranging (LIDAR), remote sensing, and secure optical communication.

Single-Photon Detection Amidst Sunlight Background

Scientists have demonstrated a groundbreaking quantum jump photodetector (QJPD) capable of detecting single photons embedded within the intense background of sunlight. This achievement overcomes a significant challenge in photon counting, requiring highly selective filtering to isolate faint signals from overwhelming noise. The research team utilized a single rubidium atom as the QJPD, successfully counting individual laser photons even when exposed to sunlight powers of approximately photons per second. The study involved developing a detailed model to accurately describe the atom’s internal state dynamics under sunlight illumination, confirming strong agreement with experimental observations.

Experiments revealed a quantum jump efficiency of 8. 5x 10-3 for single photon absorption, a 50% improvement over previous work achieved through enhanced atom localization within the trapping mechanism. Sunlight was efficiently coupled into a single-mode fiber using a tracking telescope and a series of optical fibers, delivering a maximum power of 1. 38 microwatts to the experiment.

Single-Atom Detection Amidst Bright Sunlight

This research demonstrates the successful detection of faint photon signals, at the level of single photons, even when those signals are embedded within the intense background of sunlight. Scientists achieved this by utilizing a single rubidium atom as a novel photodetector, termed a “jump photodetector”, which effectively filters out unwanted light while registering the arrival of specific photons. The team acknowledges that the AC Stark shift is relatively small for rubidium atoms but could become more significant when using atoms with narrower spectral lines. Furthermore, the researchers note that the system’s performance would improve considerably in lower-intensity backgrounds, such as skylight. Future work could focus on refining the technique by precisely matching the frequency of the desired signal to the atomic transition, potentially through tuning the emitter or manipulating the atom’s energy levels. The developed model is also broadly applicable, capable of describing the interaction between sunlight and various atomic species.