SnV centers in nanophotonic diamond devices for quantum networks: Part I- Design, fabrication and characterization of nanophotonic integrated structures

Future quantum networks require end nodes that combine excellent qubit control and coherence with efficient spin-photon interfaces. Optically active spin qubits in diamond represent an auspicious building block. Among these, the group-IV-vacancy qubits are emerging as promising candidates: thanks to inversion symmetry these systems are first-order insensitive to charge noise, rendering them compatible with the monolithic integration in photonic crystal waveguides and cavities. This would potentially increase the collection efficiency and together with the extended coherence shown at low temperature, such systems could provide entanglement generation rates beyond current state of the art.

Nanofabrication of free-hanging diamond devices is itself challenging, as there is no known wet-processing technique that allows to fabricate suspended structures starting from bulk diamond material. Moreover, the employed conventional nanofabrication methods are extensively challenged when adapted to the aforementioned devices dimensions.

Here we present our optimized fabrication process flow and demonstrate that such structures can be fabricated employing a quasi-isotropic crystal plane dependent reactive-ion-etch. We report as well on our latest experimental results and the related optical properties on the all-diamond photonic waveguides and photonic crystal cavities.