Quantum control of spin centers in silicon carbide with microcavities

Microcavities are ideal interfaces between photons as flying qubits and electron spins as stationary qubits, as they strongly enhance the interaction between light and matter. They are therefore among the foremost tools in the study and manipulation of the quantum mechanical nature of light, matter and their interactions. Silicon carbide (SiC) is a very promising material platform for wafer-scale spintronics and quantum information processing. First, this is because SiC is a material compatible with CMOS (complementary metal-oxide- semiconductor) technology, allowing construction of integrated circuits on a SiC wafer, just as silicon. Second and most importantly, spin centers in this material, particularly silicon vacancies, demonstrate an exceptionally long spin coherence time already in commercial wafers and they can be optically controlled even at the single-spin level. However, the main obstacles against applications of these centers are a low count rate from single centers and a low spin readout contrast. In this project, we will couple a single spin color center to a high quality resonator formed by a SiC chip and a silicon micromirror. This type of micromirror offers excellent surface quality, small radii of curvature and a direct path to scalability. Using resonant excitation and detection schemes, we plan to increase the spin readout contrast to above 50%. Finally, we plan to demonstrate spin-photon entanglement with a silicon vacancy in SiC, which is an important step towards implementation of quantum repeaters and networks.

Quantum systems in crystals are promising candidates for the storage of quantum information, as well as for the creation of quantum states of light. Defects in crystals such as diamond, silicon, and silicon carbide are gaining increasing interest from scientists and industry alike, as they can act as sensitive probes of the environment and may form the basis for future quantum networks and computers. While diamond has several attractive properties, silicon carbide and silicon offer a far stronger basis for technological pursuits, since they are materials of vast economic and technological importance. In SiC-EiC, we made significant strides in the development of a quantum technology incorporating these ingredients. Firstly, we developed silicon micromirrors which can reflect light back and forth over 100'000 times before it is lost. This allows us to confine photons into a very small volume, where they can then interact strongly with emitters and particles. These devices will form the basis for enhanced connections in quantum networks of defects in crystals. Secondly, we increased our understanding of these defects, with valuable insights for both materials science and for quantum technology. Finally, we developed a new way to create quantum entanglement between emitters and photons. In this method, the time at which a photon is emitted is related to the quantum state of the emitting system, which can be an atom or molecule, a quantum dot, or a spin in a crystal. We used a spin centre in diamond, and showed that it behaves in a manner that is can only be explained by quantum mechanics. These results are openly accessible, and links to selected publications are given below. Georg Wachter, Stefan Kuhn, Stefan Minniberger, Cameron Salter, Peter Asenbaum, James Millen, Michael Schneider, Johannes Schalko, Ulrich Schmid, André Felgner, Dorothee Hüser, Markus Arndt & Michael Trupke Light: Science & Applications volume 8, Article number: 37 (2019) Silicon microcavity arrays with open access and a finesse of half a million https://www.nature.com/articles/s41377-019-0145-y Rui Vasconcelos, Sarah Reisenbauer, Cameron Salter, Georg Wachter, Daniel Wirtitsch, Jörg Schmiedmayer, Philip Walther & Michael Trupke npj Quantum Information volume 6, Article number: 9 (2020) Scalable spin-photon entanglement by time-to-polarization conversion https://www.nature.com/articles/s41534-019-0236-x