Programmable 8x8 linear optical network based on silicon nitride waveguides for quantum information processing

On-chip universal linear optical networks based on tunable beam splitters and phase shifters are well suited for quantum information processing (QIP) due to their phase stability and reconfigurability. Many examples and... [ view full abstract ]

On-chip universal linear optical networks based on tunable beam splitters and phase shifters are well suited for quantum information processing (QIP) due to their phase stability and reconfigurability. Many examples and demonstrations have been given on different material platforms such as silicon-on-insulator (SOI) for, e.g., bosonic transport simulation [1] and doped silica for, e.g., universal linear optics [2].

Here, we report the demonstration of an 8x8 mode transformation circuit for quantum information processing implemented in a photonic processor based on single-mode stoichiometric Si₃N₄ waveguides [3] with propagation loss as low as 0.2 dB/cm. The advantage of this platform compared to others is the unique combination of high index contrast, enabling a dense waveguide arrangement, ultra-low straight-propagation loss and spectrally wide transparency range from the visible to the mid-infrared (Fig. 1). Our photonic processor, fully reprogrammable and remotely controllable, consists of 128 thermally tunable elements arranged in a square mesh, enabling any 8x8 transformation.

We observe on-chip quantum interference with high visibility, i.e., ~76%, on various beam splitters within the photonic processor, and we show bosonic coalescence/anti-coalescence on a 4x4 subsystem. Finally we implement high-dimensional single-photon quantum gates over the whole mode structure of the processor obtaining an average fidelity of ~95%.

Our findings demonstrate the suitability and reliability of low-loss, integrated linear optical photonic processors based on Si₃N₄ waveguides. These results show the high potential of Si₃N₄ for the development of large universal linear optical quantum circuits.

References
[1] Harris, N.C., et al., "Quantum transport simulations in a programmable nanophotonic processor" Nature Photonics 11, 447 (2017).
[2] Carolan, J., et al., "Universal linear optics" Science 349 (6249), 711 (2015).
[3] Roeloffzen, C.G.H., et al., "Low-Loss Si3N4 TriPleX Optical Waveguides: Technology and Applications Overview" IEEE JSTQE 24 (4), 1-21 (2018).