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Linear optics is a promising physical architecture for the implementation of the quantum computing devices. The key element of the linear optical quantum computer is an optical circuit realizing the sequence of transformations defined by the required quantum algorithm. The most prominent approach is the reconfigurable integrated photonics which allows to miniaturize standard optical setups on the chosen integrated photonic platform. In this paper, we propose a universal linear-optical circuit design comprised of the series of multiport beamsplitters followed by the phaseshifting elements. The proposed unitary composer device can be straightforwardly implemented using standard integrated photonic technologies. We provide guidelines for appropriate multiport beamsplitter fabrication using integrated waveguide lattices. To exemplify the performance of the composer we provide the six-mode CNOT linear optical gate circuit design fitted to described interferometric circuit. [ABSTRACT FROM AUTHOR]

The integrated photonic platform has established itself as a versatile tool for experimental implementation of linear optical quantum computations, that base on unitary transformation of the input states. In this paper we investigate the potential application of the waveguide lattice architecture to realization of arbitrary unitary matrices. We propose a waveguide lattice construction and find its parameters using methods of numerical optimization. Also we showed that a necessary lattice parameters are within the reach femtosecond laser writing technology. [ABSTRACT FROM AUTHOR]