Marilyn Monroe famously sang that diamonds are a girl's best friend, but they are also very popular with quantum scientists with two new research breakthroughs poised to accelerate the development of synthetic diamond-based quantum technology, improve scalability, and dramatically reduce manufacturing costs.
While silicon is traditionally used for computer and mobile phone hardware, diamond has unique properties that make it particularly useful as a base for emerging quantum technologies such as quantum supercomputers, secure communications, and sensors.
However, there are two key problems; cost, and difficulty in fabricating the single-crystal diamond layer, which is smaller than one-millionth of a meter.
A research team from the ARC Center of Excellence for Transformative Meta-Optics at the University of Technology Sydney (UTS), led by Professor Igor Aharonovich, has just published two research papers, in Nanoscale and Advanced Quantum Technologies, that address these challenges.
Professor Aharonovich said, for a diamond to be used in quantum applications, we need to precisely engineer optical defects in the diamond devices cavities and waveguides to control, manipulate and read out information in the form of qubits, the quantum version of classical computer bits. It's akin to cutting holes or carving gullies in a super-thin sheet of diamond, to ensure light travels and bounces in the desired direction.
To overcome the etching challenge, the researchers developed a new hard masking method, which uses a thin metallic tungsten layer to pattern the diamond nanostructure, enabling the creation of one-dimensional photonic crystal cavities.
Lead author of a paper in Nanoscale, UTS Ph.D. candidate Blake Regan said, the use of tungsten as a hard mask addresses several drawbacks of diamond fabrication. It acts as a uniform restraining conductive layer to improve the viability of electron beam lithography at nanoscale resolution.
To the best of our knowledge, we offer the first evidence of the growth of a single crystal diamond structure from a polycrystalline material using a bottom-up approach like growing flowers from seed.
He said, it also allows the post-fabrication transfer of diamond devices onto the substrate of choice under ambient conditions. And the process can be further automated, to create modular components for diamond-based quantum photonic circuitry.
The tungsten layer is 30nm wide around 10,000 times thinner than a human hair, however, it enabled a diamond to etch of over 300nm, a record selectivity for diamond processing.
A further advantage is that removal of the tungsten mask does not require the use of hydrofluoric acid one of the most dangerous acids currently in use so this also significantly improves the safety and accessibility of the diamond nanofabrication process.
To address the issue of cost, and improve scalability, the team further developed an innovative step to grow single-crystal diamond photonic structures with embedded quantum defects from a polycrystalline substrate.
UTS Ph.D. candidate Milad Nonahal, lead author of the study in Advanced Quantum Technologies said, Our process relies on the lower-cost large polycrystalline diamond, which is available as large wafers, unlike the traditionally used high-quality single crystal diamond, which is limited to a few mm2. To the best of our knowledge, we offer the first evidence of the growth of a single crystal diamond structure from a polycrystalline material using a bottom-up approach like growing flowers from seed.
UTS Dr. Mehran Kianinia, a senior author on the second study said, Our method eliminates the need for expensive diamond materials and the use of ion implantation, which is key to accelerating the commercialization of diamond quantum hardware.
Nanofabrication of high Q, transferable diamond resonators is published in Nanoscale.
Bottom-Up Synthesis of Single Crystal Diamond Pyramids Containing Germanium Vacancy Centers is published in Advanced Quantum Technologies.