Abstract

Quantum computing with linear optics mandates the interaction between two photons via the Hong-Ou-Mandel effect [1]. Such effect is typically achieved in linear beam splitters. Two-port beam splitters have been realized in integrated optical technology for quantum logic gates, quantum metrology and quantum information processing [2]. The general scheme for a two-port beam splitter in a linear implementation is shown in Fig. 1(a), where θ₁ (θ₂) is the phase difference between the two output ports O₁ and O₂ considering the input beam from I₁ (I₂). Lossless beam splitters produce a phase sum α= θ₁ + θ₂ = π at the output ports of the beam splitter (see Fig. 1(b)). Based on the Hong-Ou-Mandel effect, the phase α affects the quantum interference between two photons. However lossless beam splitters do not allow the tunability of α. Here we demonstrated that beam splitters can be designed with exact phase control, and thus tunable α, using adjoint-based topology optimization.

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