Abstract: A method for robust state manipulation in quantum information processing comprises evanescently coupling a first waveguide to a second waveguide, the first and second waveguide having different geometries respectively; and providing waveguide geometries such that their coupling is detuned, the detuning being a function of the geometries, the detuned coupling thereby providing reliable population transfer between the first and second waveguides that is robust to fabrication and other errors. The method may be used to provide a quantum optical coupler.

Abstract: A method for constructing a quantum gate for a unitary operation in photonic quantum information processing, comprises: providing two or more waveguides, calculating segment parameters for segments within a coupling region, said one or more parameters relating to propagation constants of respective waveguides, said one or more parameters being different for said first and second waveguides respectively and thereby providing detuning between said first and second waveguides to allow for unitary operation between said first and second waveguides with high fidelity in the presence of errors, then building the segments into the respective waveguides and optically coupling the waveguides at the coupling region using the segment parameters, thereby to construct a quantum logic gate for a unitary operation.

Abstract: A method for robust state manipulation in quantum information processing comprises evanescently coupling a first waveguide to a second waveguide, the first and second waveguide having different geometries respectively; and providing waveguide geometries such that their coupling is detuned, the detuning being a function of the geometries, the detuned coupling thereby providing reliable population transfer between the first and second waveguides that is robust to fabrication and other errors. The method may be used to provide a quantum optical coupler.