Large-scale quantum entanglement endows quantum technologies with significant quantum advantages over their classical counterparts. Nevertheless, this power is rarely unleashed due to our practical inefficiency in generating multiphoton entanglement. Here, we implement an active entangled-state time-multiplexing method, which can generate $2n$-photon entangled states with an exponential efficiency-enhancement factor of $B^{n-1}$. We experimentally achieve a multiplexing power of $B=6.43$ in preparing four-photon Greenberger-Horne-Zeilinger states with fidelities above 0.806(5), which is mainly limited by technical loss in multiplexing. Even with current multiplexing power, our method can readily boost the efficiency of preparing 12-photon entangled sources by a factor of ${6.43}^5\approx {10}^4$. Our work demonstrates that entangled-state time multiplexing promises a path toward efficiently preparing and harnessing multiphoton quantum entanglement for unprecedented large-scale quantum computation and high-precision quantum metrology.

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• Entanglement production
• Optical quantum information processing
• Photon pairs & parametric down-conversion
• Quantum entanglement
• Quantum optics
• Quantum state engineering
• Multiplexers