Diamonds inside – new medium for quantum information – talking papers #4
Quantum information science promises to be a next big thing. Diamond nano-crystals can be made to exhibit quantum behaviour through single photon emission but are extremely fiddly to manipulate. Microstructured optical fibres provide a great platform for interacting light with matter and transmitting information over potentially large distances at very low cost. By mixing diamond nano-crystal powder into tellurite glass & taking it through a well established process to create microstructured fibre, IPAS researchers have paved the way for future work that might give us ways to create simple, effective, cheap technologies that bridge quantum/classical, potonic/electronic & nano/micro/macro scale environments. These technologies could well provide industry with new tools for the creation of devices that can send perfectly secure quantum messages, re-define the standard for how we measure light intensity & create new types of sensors.
The paper “Diamond in Tellurite Glass: a New Medium for Quantum Information” published in Advanced Materials shows the world a new hybrid material with implications for quantum information processing and is understandably attracting quite a lot of attention. The fundamental question posed by this research is: if diamond nano-crystal powder is mixed into molten glass, will the special properties of those crystals be retained in a useful way? To answer this question the team made several ‘billets’ of tellurite glass mixed with diamond nano-crystals, extruded them into structured ‘pre-form’ rods which were then drawn into Micro-structured Optical Fibres ‘MOF’. Team members from the University of Melbourne then examined the fibres to see how the crystals were distributed in the glass and performed tests to see if they retained their special single photon emission property.
As Melbourne based collaborator Andrew Greentree explains in the audio that accompanies this writing, the diamond nano-crystals are commercially available and were carefully selected for their emission properties and likely ability to survive the fibre fabrication process. These particular crystals have a nitrogen vacancy colour centre that emits light (as single photons) at a rate of about one every 10 nano-seconds. This is a very bright emission that can be seen through a microscope – unlike the tiny (30 nm diameter) crystals themselves. That said, special skills and a computer controlled microscope were required to find and count the crystals in a section of the special tellurite glass fibre.
Matt Henderson gives us a sense of how tricky it was to mix the diamond powder into the glass and to prevent bad things from happening to the tiny nano-crystals at high temperatures. While the crystals did mix with the molten glass, they tended to ‘clump together’ in these early fabrication runs. Using even smaller quantities of diamond powder and distributing it more evenly throughout the glass will be a focus of future work. Matt also points out that it is not exactly easy to find small numbers of tiny crystals in a ‘huge’ (about the width of a human hair and a few centimetres long) piece of fibre. These images show the light emitting from the diamond nano-crystals as a laser is aimed into the fibre.
The great news is that despite the perils of exposing the diamond nano-crystals to a rather harsh process and their tendency to clump together in the glass, it is still possible to detect single photon emission from a piece of the special micro structured fibre. This is shown in the classic ‘V’ dip in the chart at figure 3c in the paper. The challenge for future research will be to fabricate a much smaller fibre with far fewer diamond nano-crystals and to couple that fibre with a laser in such a way that exactly one photon is emitted each and every time the laser is fired. A source like this could be used to send perfectly secure quantum messages, re-define the standard for how we measure light intensity & react that nano particle with its environment to create new sensors.
Pretty cool eh? IPAS director Prof Tanya Monro thinks so and is particularly optimistic about the potential for this approach which harnesses properties unique to the nano-scale in a platform that is able to be fabricated and manipulated at the macro or micro scale. This blend of materials science, photonics & nano-tech is definitely an area to keep an eye on – and watch out when a cheap, reliable, robust single photon source is developed. I think that will turn out to be one of those ‘tipping points’ we will look back on, possibly through the output device of our shiny new quantum computer.
Mike Seyfang for IPAS “talking papers” series.
IPAS would like to acknowledge the work of all collaborators listed in the paper and the support from the ARC through Federation and QEII fellowships.