Single-gate, multipartite entanglement on a room-temperature quantum register

Abstract

Multipartite entanglement is an essential aspect of quantum systems, needed to execute quantum algorithms, implement error correction, and achieve quantum-enhanced sensing. In solid-state quantum registers such nitrogen-vacancy (NV) centers in diamond, entangled states are typically created using sequential, pairwise gates between the central electron and individual nuclear qubits. This sequential approach is slow and suffers from crosstalk errors. Here, we demonstrate a parallelized multi-qubit entangling gate to generate a four-qubit GHZ state using a room-temperature NV center in only 14.8 $\mu$s $-$ 10 times faster than using sequences of two-qubit gates and close to the fundamental limit set by the hyperfine coupling frequencies. Parallel three-qubit gates are also realized with all nuclear-qubit subsets. The entangled states are verified by measuring multiple quantum coherences. The four-qubit parallel gate has a fidelity of 0.92(4), whereas the sequential four-qubit gate fidelity is only 0.69(3). The approach is generalizable to other solid-state platforms, and it lays the foundation for scalable generation and control of entanglement in practical devices.