Resource-efficient linear-optical generation of GHZ-like states

Abstract: Heralded multi-photon entanglement generation is a central bottleneck for photonic quantum computing, where resource costs typically skyrocket with target size. We explore efficient methods for generating photon states with tunable entanglement, providing a flexible tool for quantum state engineering. We introduce a theoretical framework that has been numerically validated, demonstrating the capacity to generate GHZ-like states incrementally from non-logical intermediate states. We demonstrate that in certain scenarios $-$ such as reducing the resource cost for building large maximally entangled GHZ states $-$ these variable-entanglement states can outperform their fixed-entanglement counterparts. By adjusting intermediate states and optimizing interferometer schemes, we improve photon number cost efficiency of GHZ-like states generation. Our findings indicate that while not a universal solution, non-maximally entangled states offer practical advantages for specific photonic quantum information tasks.