New photon avalanche nanoparticles may usher in the next generation of optical computers

A research team led by Lawrence Berkeley National Laboratory (Berkeley Lab), Columbia University, and Autonomous University of Madrid has successfully developed a novel optical computing material using photon avalanche nanoparticles. This breakthrough achievement was recently published in the journal Nature Photonics, paving the way for the manufacture of optical memory and transistors at the nanoscale (comparable in size to current microelectronic devices). By utilizing an optical phenomenon called 'intrinsic optical bistability', this method provides the possibility to achieve smaller and faster next-generation computer components.

This is the first time that the existence of intrinsic optical bistability has been practically verified in nanomaterials, "said Emory Chan, a molecular foundry scientist at Berkeley Laboratory and co first author of the paper." We are not only able to stably prepare such materials, but also have a deeper understanding of their counterintuitive properties, which is crucial for achieving large-scale optical computers
Postdoctoral researcher Xiao Qi is in the laser room of Molecular Foundry.

This research is an important component of Berkeley Lab's overall strategy to promote the development of smaller, faster, and more energy-efficient microelectronic devices through new materials and technologies.

For decades, scientists have been dedicated to developing new computers that replace electricity with light. Materials with intrinsic optical bistability (IOB) - the ability to switch between two states (such as bright light emission and complete extinction) through optical signals - are expected to become the core components of optical computers. However, the optical bistability in previous studies mainly appeared in bulk materials, which have a size far beyond the requirements of microchips and are difficult to mass produce. Although there have been occasional reports of nanoscale IOB, its mechanism is still unclear and is usually attributed to the heating effect of nanoparticles, which is inefficient and difficult to control.

However, the latest research by Chan and his team suggests that the novel photon avalanche nanoparticles have the potential to overcome the challenges of achieving nanoscale IOBs. In experiments at the Berkeley Laboratory Molecular Foundry (Nanoscience User Facility), researchers prepared 30 nanometer nanoparticles using potassium lead halide materials doped with neodymium (a rare earth element commonly used in lasers). When excited by infrared laser, these particles exhibit a "photon avalanche" phenomenon: a small increase in laser power can lead to a disproportionately large increase in particle luminescence intensity. The team discovered this "extremely nonlinear" characteristic as early as their groundbreaking paper in 2021, when experiments showed that doubling laser power could increase luminous intensity by tens of thousands of times.

In the latest research, the team found that the nonlinear strength of the new nanoparticles is more than three times that of the original avalanche particles. Chan emphasized, "This is the highest observed nonlinearity value of the material so far." What is even more surprising is that further experiments have shown that these particles not only exhibit avalanche characteristics when exceeding a specific laser threshold, but also continue to emit light even when the power drops below the threshold, completely extinguishing only at extremely low power. This means that these tiny particles are exactly the IOB materials that nanoscientists have been pursuing for a long time.

Chan explained that the significant difference between the "on" and "off" thresholds indicates that in the intermediate power range, the brightness of nanoparticles depends only on their historical state. The ability to switch optical properties without changing the material itself makes it an ideal candidate for nanoscale optical memory, especially volatile random access memory.

To investigate the physical mechanism of bistability, researchers have revealed for the first time through computer modeling that the IOB of nanoparticles does not originate from thermal effects, but from the extremely nonlinear characteristics of photon avalanche and the unique structure that suppresses particle vibration. Future research will focus on exploring new applications of optical bistable nanomaterials and seeking novel nanoparticle formulations with higher environmental stability and optical bistability.

Molecular Foundry is a nanoscience user facility under Berkeley Lab. This study was funded by the Office of Science at the US Department of Energy and received additional support from the Defense Advanced Research Projects Agency (DARPA) and the National Science Foundation.

Source: opticsky