Scalable long-distance quantum fan-out gates with reduced resource overhead

Abstract

Scalable long-distance quantum gates are essential for distributed quantum computation and scalable quantum networks. We propose an efficient scheme for implementing an $n$-qubit fan-out gate $C^n$ (also known as a controlled-NOT-$\cdots$-NOT gate) across spatially separated parties. Our protocol requires only a pre-shared $n$-qubit Greenberger-Horne-Zeilinger state, $n$ local controlled-NOT (CNOT) gates, and feed-forward operations, thereby reducing both the CNOT and Hadamard gate counts by $(n-2)$ when compared with the standard decomposition-based approach. We further develop two optical architectures to implement the heralded and post-selected $n$-photon fan-out gates, respectively. These schemes require fewer single photons resources and achieve higher success probabilities than their decomposition-based counterparts, representing significant improvements. The results indicate that our approach is experimentally feasible and pave the way toward practical long-distance quantum computation.

18 pages, 8 figures