Highly Efficient Low Loss Fiber-Chip Light Coupling for Quantum Networks

Superconducting and photonic qubits are the leading platforms for quantum computation, now and for the foreseeable future, and will provide essential functionality to large-scale quantum networks. To achieve this, techniques are needed to coherently convert between the microwave states used by the qubits and optical states required for long-distance communication, a conversion that needs to occur at cryogenic temperature (< 100 mK). This is an active field of research that follows several parallel technicalities, which are hampered by one common bottleneck: the ability to efficiently couple light between optical fibers and Photonic Integrated Circuit (PIC) waveguides. The inefficiency of current coupling schemes not only reduces the fidelity of the interconversion by photon loss, but light scattered from fiber-to-chip interfaces is highly detrimental to qubits and other superconducting circuit elements that are needed for the interconversion process. HighRI Optics Inc., in collaboration with Molecular Foundry at Lawrence Berkeley National Laboratory (LBNL), and BBN Raytheon, proposes to develop a novel lensed fiber for efficient fiber-to-chip coupling. The high refractive index lens will be imprinted on a single-mode fiber facet with an in-house fiber imprinter. Such a lens can still function in polymer mediums used for photonic packaging and can efficiently focus light into the waveguide while bonded at room or cryogenic temperature. This method can lead to low-cost manufacturing to accelerate commercialization, and the method is broadly adaptable for the photonic packaging community. Packaging of integrated photonic circuits (PIC) or miniaturized medical devices requires tedious placement and active alignment of the various micro-optical elements to each other. Coupling losses lead to significant contributions to the link power budget for digital computing and communications applications. The technological goal of this project applies only to quantum networks but also to the integrated photonics packaging currently in use, especially in telecommunications and data centers.