Enhancing European metrology for practical quantum sensors based on diamond
Challenge
At the quantum level, fundamental particles have counterintuitive properties. They can exist in multiple states simultaneously, a phenomenon, termed “superposition” (electrons or photons can be both “1” and “0” at the same time), or be correlated in a nonclassical way, no matter how far apart they are (the so-called “entanglement”). The quantum state is fragile and the minimum interaction of the particle with the environment can alter it (“decoherence”). Quantum sensors (QS) exploit this sensitivity to external influences to make equally supersensitive measurements in areas including medical diagnosis, navigation, or environmental monitoring.
One form of QS is based on randomly implanting atoms into synthetic diamonds. If implantation occurs next to an empty space in the diamond lattice, a “colour centre” is created. When interacting with its environment it emits light encoded with information, acting as a sensor for external influences such as magnetic and electric fields. Implantation of nitrogen atoms creates nitrogen-vacancy (NV) centres, however, the performance these QS is highly dependent upon the location of the nitrogen which can affect its spectral stability or, if near the surface, decoherence time. Other atoms, such as silicon or germanium, have demonstrated superior spectral stability but standardised techniques for realising nanoscale QSs, including synthesis processes to produce material with reproducible performance and quality, were lacking.
Solution
During the QADeT project, the University of Torino - in collaboration with external colleagues of Italian Fondazione Bruno Kessler - employed a custom ion implantation process with alignment techniques. A focused ion beam implanted germanium ions (Ge2+) with sub-100 nm precision into a high purity diamonds distributed into sets of 10 x 40 arrays. The arrays were subsequently overlapped with nanopillars fabricated by project partner QNAMI, with the aim of trapping GeV colour centres into the 300 nm tip of each pillar. To tightly control the position and depth of Ge2+ ions beam energy ranges of 35 keV and 70 keV were used. GeV centres could now be studied in combination with nanopillars acting as optical waveguides. Results indicated up to 33% of the fabricated nanopillars contained single photon emitters, providing an 8-fold increase in photoluminescence signal-to-background ratio, a considerable improvement on the current state of the art.
Furthermore, pre- and post-characterisation indicated that the nanopillar fabrication process did not affect the quantum properties of the GeV centres.
Impact
QNAMI is a world leader in quantum sensor technology and in the development of quantum sensing and imaging applications, providing analytical solutions for applications in nanotechnology, spintronics and failure analysis. Due to this expertise, the company was asked to join QADeT to produce a range of samples at their Quantum Foundry facility, including the manufacturing of optical waveguides in the form of nanopillars. Through the work performed, longstanding questions concerning diamond fabrication were answered, further expanding the knowledge QNAMI has in finetuning ion implantation for specific quantum applications. This will be translated into improved products for their customers and, in time, their own such as the ProteusQ, the first NV microscope for analysing magnetic materials at the nanoscale.
Controlled ion implantation and characterisation methods are essential steps for developing practical and stable QS. The diamond nanopillars developed, for example, act as “waveguides” for incorporation into practical quantum applications, including photonic chips for quantum computers. The development of target Ge2+ ion implantation will serve as a basis for expanding the use of diamond-based QS in a wide variety of fields, including physics, data storage and diagnostic imaging.
This is one of the very first instances where, through the effort of QADeT, newly developed tools to realise practical QS by the metrological institutes exist to take these beyond the prototype stage, allowing Europe to meet its quantum goals. Work continued in the follow-up project NoQTeS.
- Category
- EMPIR,
- Industry,
- New Technologies,
- EMN Advanced Manufacturing,