Photonic quantum gates are fundamental building blocks for a wide range of optical quantum information processing tasks. We propose an efficient linear-optical scheme for implementing a postselected three-qubit fan-out gate (also known as a controlled-not-not gate) using only two ancillary single photons and linear optical elements. The scheme can be generalized to an $n$-qubit fan-out gate, requiring $(n-1)$ ancillary single photons and $(3n-3)$ polarizing beam splitters (PBSs), with a success probability of ${(\frac{1}{4})}^{n-1}$. Compared with the standard gate decomposition approach, which requires $(2n-2)$ ancillary single photons, $(5n-5)$ PBSs, and yields a success probability of ${(\frac{1}{8})}^{n-1}$. Our scheme significantly reduces the resource overhead and improves the success probability. We further evaluate the gate performance and demonstrate improved robustness compared with gate decomposition-based methods.

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• Optical quantum information processing
• Photonics
• Quantum computation
• Quantum gates
• Quantum optics