State preserving fiber-to chips coupling of photonic qubits

Optical interconnects are at the heart of today’s information technology as they are the link that enables humanity to benefit from cloud-based computing, mobile streaming, instantaneous messaging and communications etc. Like many technologies optics rely on hybrid systems such as photonic chips for data processing and optical fibers for long-haul transmission and coupling schemata are needed to combine them. The achievable efficiency depends on the coupler method (grating coupler, edge couple​r, evanescent coupler) and in general achieving larger efficiencies comes at the cost of more complex fabrication, larger footprint or vertical alignment. For instance, edge coupling with transmission loss of ~0.25dB  (~5.5%) have been reported, while more compact grating couplers achieve transmission losses of ~0.5dB (10.8%).

And while this performance is already good for classical applications it does not suffice for the more stringent requirements of quantum applications. The issue of the limited coupling efficiency is even more important as photonic based quantum systems is a tremendous engineering task and a monolithic platform (e.g. silicon photonics) cannot meet all the requirement simultaneously. Heterogenous integration of different quantum technologies (silicon photonics, III-V single photon source, superconducting single photon detectors) in a single functional unit have great potential to overcome the obstacles. However, coupling losses at each technology interface contributes noise that causes decoherence of the quantum state. In this work we will push the coupling efficiency towards unity .