Thanks to a collaboration between the research groups led by Shane Eaton of the Institute of Photonics and Nanotechnology of the National Research Council (Cnr-Ifn) of Milan and by Alexander Kubanek of the University of Ulm, an innovative manufacturing method has been developed and hybrid to make photonic circuits using diamond: an essential step to develop quantum bits (qubits), the building block of quantum information. Quantum networks are based on systems connected to each other for the transfer of information, exploiting quantum-mechanical properties such as entanglement and superposition of states. The ability to modify light at the single photon level in an integrated device is a fundamental requirement for developing the new generation of quantum networks: this will make it possible to build advanced computers to solve some complex problems more and more quickly, but also to use communication channels safe to transfer encrypted information.
“In diamond there are, and can be suitably engineered, lattice defects capable of being used as qubits”, explains Shane Eaton, researcher at the Cnr-Ifn. “These are color centers, reticular positions where an impurity is present and a carbon atom is missing, and where it is possible to encode, control and manipulate quantum information in the form of qubits. This particular morphology – and the presence of these defects – makes diamond a promising candidate for quantum technologies”. The Italian team, together with colleagues from the University of Ulm, demonstrated that it is possible to precisely place qubits based on silicon-vacancy centers within photonic circuits formed using diamond lasers.
“These results arise from the first demonstration (Eaton, Nature Scientific Reports, 2016) that femtosecond lasers – i.e. lasers that emit very short and close pulses, a femtosecond being one millionth of a billionth of a second – can create photonic connections in diamond, which are the building blocks needed for quantum computing,” explains Eaton. “Another fundamental ingredient is, then, that of creating qubits: with this new technique we have developed a chip integrated in diamond, capable of engineering light at the single photon level. The next step will be to fabricate a three-dimensional photonic circuit to make possible next-generation quantum computing systems in diamond, such as to allow for the processing of a considerable amount of data simultaneously, with extreme speed”, specifies the researcher.
The importance of these issues, both at a fundamental and technological level, has also recently been demonstrated by the awarding of the Nobel Prize for Physics 2022 to Alain Aspect, John Clauser and Anton Zeilinger: these results therefore assume great importance for the future development of cutting-edge quantum technologies. This work was made possible thanks to the Marie-Skłodowska-Curie innovative training network (ITN) programme, a European funding coordinated by Eaton, with the collaboration, among others, of the Doctoral School of the Milan Polytechnic. “Our ITN allows the training of 13 promising PhD students, in European laboratories, both university and industrial, in interdisciplinary fields. In this case, collaboration with our partner, the University of Ulm, has led us to this new discovery, which will have a major impact on the imminent quantum revolution and the future of computing,” concludes Eaton.