Chip-scale interface based on four-wave mixing Bragg scattering for noiseless coherent wavelength translation
Imad Agha, Marcelo Davanco, Bryce Thurston, and Kartik Srinivasan
A coherent interface for wavelength translation is an indispensable part of future quantum networks, potentially enabling hybrid approaches for quantum device applications . Photons, the ubiquitous information carriers in quantum systems- often referred to as “flying qubits” - do not always possess the ideal wavelength for a particular application. A coherent wavelength translation interface allows matching the photons to any system with which they interact down the line. Both c(2) and c(3) nonlinear optical processes can be used to implement such an interface  . To enable coherent wavelength translation in silicon-based systems, c(3) processes are generally favored due to the lack of a strong second-order nonlinearity in these materials. Here, we make progress towards wavelength translation in an integrated, Si-based platform by demonstrating the process of non-degenerate four-wave-mixing Bragg scattering (FWM-BS) in Silicon Nitride (SiNx) waveguides .
In FWM-BS, two non-degenerate pumps at frequencies w1 and w2 (w1 > w2) scatter photons from a signal at ws to an idler at wi. The conditions under which this process is optimal are referred to as phase-matching conditions and can be attained by properly engineering the waveguide nanostructure. We first verify the appropriate dimensions and geometry via numerical simulations that account for both the linear and nonlinear optical properties, and then proceed to fabricate the nanostructures in the Center for Nanoscale Science and Technology’s (CNST) cleanroom facility. After fabrication, we test the potential of our SiNx waveguides as an interface for coherent wavelength translation by showing tunable conversion of 980 nm band signals via non-degenerate telecommunications - band pumps with conversion efficiency reaching 5%. We target the 980 nm band due to the potential for future integration with quantum dot single photon sources that typically emit between 900-1000 nm and are strong candidates for flying qubits in future quantum networks. After testing the performance of our waveguiding structures in the classical optics domain, we implement noise studies to characterize its performance as a noiseless quantum interface for coherent wavelength translation.