By the fourth century AD, the ancient Romans had become so talented at glassmaking that it had become one of the most distinguished art forms of the time. Today, the Lycurgus Cup is a testament to the accomplishments of the ancient Roman glass industry and it stands majestically – almost fully in tact – in the British Museum. The cup is one of the rarest objects in the world because it is one of but a handful of ancient Roman cups still around today which have the peculiar feature of being “dichroic”; that is, able to change colours. Depending on the way light hits them (whether in transmission or reflection), these dichroic glass cups transform from one colour to another. But it is the Lycurgus Cup which completes this optical trick the best, as its colours are still strong and vibrant, illuminating a set of images carved into the glass of King Lycurgus (a character from The Illyad) while in battle with the Greek god Dionysus.
When light shines through the cup (if it is lit up from behind – in transmission) the glass is a purple-red. But when the light reflects off of it (when it is lit from the front – in reflection) the glass turns jade green. It took a long while for people to realise how the optical transformation took place. When microscopic and x-ray technologies developed in the twentieth century, researchers took broken fragments of the glass away to investigate them, finding tiny proportions of gold, silver and other metals. It turned out that the glass was specked with nanoparticles of these metals, which were dispersed in colloidal form throughout the glass material. These colloidal systems, or crystals, were found to scatter light in different ways depending on the way the light hit them (see source here).
No one knows how the Romans managed to achieve this effect, but it is doubtful it was achieved by accident. The metals in the Lycurgus Cup would have needed to be ground down into such miniscule particles, and placed into the meld of ingredients at such particular concentrations (so as to emanate the desired colours), that it would have required careful experimentation. Some people are still unconvinced however, suggesting that the cup must have been contaminated with dust or left over gold particles from other works, because other surviving pieces from the same era appear to be failed attempts at recreating the effect. At any rate, this shows that the Romans were among the first to experiment with nanoparticles, attempting to use them to create magnificent works of art.
From Ancient Glassmakers to Modern Optics
Modern science is picking up where the ancient Romans left off, and Australian researchers are leading the way in trying to perfect the art of manipulating the optical properties of nanoparticles. At the helm of this new research are scientists from the University of Adelaide’s Institute of Photonics and Advanced Sensing (IPAS). Associate Professor Heike Ebendorff-Heidepriem, who is a Senior Research Fellow in the University’s School of Chemistry and Physics, is one of these scientists. Her glassmaking abilities would make even the ancient Romans marvel, though she has much more advanced technology and scientific understanding at her disposal. She is now working on her own Australian Research Council Discovery Project looking at how to exploit the optical properties of gold nanoparticles in glass, nearly two millennia after the Romans tried to do the same with their glasswork.
Her research into gold nanoparticles came into fruition after working on another Discovery Project looking at developing nanodiamond-infused optical fibers to use for magnetic field sensing, led by IPAS director Tanya Monro. In an experiment where Ebendorff-Heidepriem tried to embed glass with nanocrystals, she found the glass she created had changed colours, just like the Lycurgus Cup. “I made a glass which had a nice blue colour in transmission, and a brown colour in reflection,” Ebendorff-Heidepriem told me. “I looked into what could cause this phenomenon, and I came across gold nanoparticles, which led me to the Lycurgus Cup. I was so fascinated with the parallels between the cup and the glass that I made by accident, which already had the nanocrystals in it,” she said.
Ebendorff-Heidepriem hopes to prove in her research that the nanocrystal she melded into her glass sample formed into gold nanoparticles during the process, which resulted in the light-scattering which caused the cup’s dichroic effect (though it created different colours to the Lycurgus Cup due to the different concentrations and types of particles used).
Whereas there is some confusion as to the Romans’ awareness of what they were doing, Ebendorff-Heidepriem’s understanding of the process is crystal-clear. Finding conventional methods of embedding glass with nanocrystals problematic, she tried a new method in her experiment. “The current technique to get nanocrystals into glass is to heat up the glass by a certain annealing process, and – only for certain compositions of glass – crystalise the nanocrystals into the glass,” she explained. “This is comparatively limiting, because you’re limited to certain glass compositions and to certain annealing or heat treatment regimes.”
“There are now (research) papers coming out where people are making nanocrystal solutions in the form of a powder. So what I want to do is take this ‘powder’ of nanocrystals and place it directly into the meld so that I can combine the flexibility of the glass composition and the flexibility of the nanocrystals.”
The analogy she used to describe the process was to picture the glass as a solid solvent. This solvent preserved and protected the nanocrystal properties placed into it in powder form because they became embedded into a solid matrix. As a result, the nanoparticles were encased in the glass so that the glass could reflect their properties and protect them from degradation. In effect, this is how the Lycurgus Cup, and the other samples of ancient Roman dichroic glass, worked.
Aside from the artistic appeal of changing an object’s optical properties (as per the Lycurgus Cup), exploiting these nanoparticles has some practical applications too. Glass impregnated with nanodiamonds could, for instance, increase the luminosity of light sources without using up as much energy, improving their energy efficiency. Optical fibers embedded with nanodiamonds could also be used for advanced sensing applications, which require a light source on a very small scale, or as mini information carriers, assisting in the field of quantum computation. Other uses have been envisaged for telecommunications, medicine and solar cell technology.
Perfecting the craft of quantum mechanics research
Yet one of the more important benefits of embedding diamond in optical fiber is simply the potential it may afford to innovate our mastery of quantum mechanics and nanotechnology writ large. If coming up with new inventions to improve our grasp of difficult scientific concepts was a craft, then Associate Professor Andrew Greentree would be its craftsman. A research fellow at the School of Applied Sciences at the Royal Melbourne Institute of Technology (RMIT), with a background in quantum physics, Greentree has been collaborating on the project with Ebendorff-Heidepriem and her colleagues at IPAS. They have also been joined by Brant Gibson, a colleague of Greentree’s at RMIT. While Ebendorff-Heidepriem makes the samples, Gibson makes the single particle measurements to quantify the samples’ results, while Greentree interprets the results, theorises about what’s going on and offers suggestions of new ways of doing things.
For Associate Professor Greentree, the endeavour is as much about the fundamental science it teaches us as it is about coming up with new technologies. He wants the new devices to spur another generation of scientists and students to theorise and ponder about the fundamental science behind these devices and what can be done with them. To him, inventions like this are “new games” for people “to come up with new ways of seeing the world”. It is his goal to devise these new games, to enhance our ability to learn about the science behind them.
“We already know the rules of the game when it comes to quantum mechanics,” he told me. “But we’re so far away with knowing what we can do with it. Ultimately what we want to do is to make new quantum devices or quantum-enabled devices and then just throw them out there. Just to see what can be done, get people playing with them.”
He believes diamond-in-fiber devices like Heike’s, which provide an easily accessible and manageable quantum-mechanical state of light, can be given to engineers, students, or even schoolkids so they can play with and interrogate them. In this way, it may allow students of the future to think about quantum mechanics as second nature. This could, if Greentree is right, revolutionise the way nanoparticle research is practiced. It will bring the nano-world away from the textbook, or from the mathematical equations on the whiteboards in lecture-theaters, and into students’ very hands.
As an example, Greentree speculated about the possibilities diamond-in-fiber could open up for the relatively new field of quantum metrology. Quantum metrology is what Greentree described as “the push to redefine how we measure light intensities based on quantum mechanics”, though it could be defined more loosely as the study of measuring any quantum-level physical system using quantum theory. “Diamond, and particularly colour centre effects of diamond, have turned out to be one of the really interesting new and easily accessible quantum systems,” Greentree explained to me. “But the problem of how to measure and initialise these particles is a difficult one, and that’s where the diamond-in-fibre really comes into its own.” This problem would be neutralised because housing the nanodiamond, with its colour centre effects, within optical fibers would allow researchers and engineers to have an “easily accessible quantum system” that is locked within a solid glass cage, so to speak. The diamond’s properties, such as its light intensities, can therefore be quantified more easily, and this new data can be applied against the backdrop of what we know about quantum mechanics.
But that’s not to say Greentree doesn’t value the potential technological applications this research could enable for either. One area of interest which he said diamond-in-fiber technology could help out with is quantum cryptology. If optical fibers can efficiently store these nanodiamonds – should the research undertaken by Greentree and IPAS prove successful – this provides an identifiable quantum system that can be used to perform tasks like sharing quantum secret keys (which are, to use a very crude analogy, the equivalent of nano-scale hard drives which two parties can use to encrypt or decrypt messages). The significance this bears for the fields of intelligence-gathering, surveillance and communications can hardly be understated.
How to produce a nanotechnology masterpiece
The ideas that resulted from the collaboration were quite unique, Greentree felt. “This is definitely something that we’re leading and we’re the only people doing,” he said. “There are lots of people looking at trying to find ways of coupling diamond and other nanoparticles to fibre. Most of that work is being done by putting the diamond on the outside of the optical fibres, and that has certain advantages. But certainly we’re leading the research into diamond inside the optical fibre and we think it’s the best approach.”
He also admitted it was a hard approach: “One of the reasons why no one else is doing it is because it takes a mixture of people who are very good at glasses and sensing – as Adelaide (University) is. But at that level of optics, they have to team up with people with expertise in single particle measurements and quantum theory. And that’s what we provide at RMIT.”
So it takes a group of skilled nanoparticle researchers to perfect the art of nanotechnology; someone to lay out the theoretical basis underpinning the artwork, someone with the engineering skills to understand and implement this theory and design the piece, and someone with the vision to be able to see into the nano-scale realm and measure and analyse the particles involved.
While creating art may not be the researchers’ end goal in inseminating glass with nanocrystals, their careful process of planning and experimentation, and their passion for inventing something new and meaningful, betray the features of dedicated artists. It can also be said that they are contributing to a long succession of scientists and engineers who have tried to add one more piece into the jigsaw puzzle that is the world around us. It is this undying pursuit of trying to expose some truth about nature which makes all scientists a type of artist. Nevertheless, it is fair to say Ebendorff-Heidepriem and Greentree have perfected an artistic process that the ancient Roman glassmakers tried to master but couldn’t entirely – that is, manipulating the optical properties of nanoparticles – thereby completing an unfinished chapter in the history of art.