NV-Center 7-Qubit Register Reaches 99.61% Two-Qubit Gate Fidelity, Crossing Distributed Quantum Computation Threshold

The work optimizes pulse sequences to suppress crosstalk in the densely connected spin system around the NV center. Researchers applied an efficient numerical procedure to calibrate controlled-phase gates between the electron spin and multiple 13C nuclei, then validated performance with gate set tomography on the full register. This approach directly addresses the multi-qubit error accumulation that has limited prior solid-state network nodes.

The achieved fidelities place the register at the surface-code threshold for distributed quantum computation when combined with existing optical entanglement protocols. Prior NV experiments reached high single-qubit and entanglement fidelities but fell short on simultaneous multi-qubit gates; this result closes that gap. The VQE demonstration on H2 and LiH ground states further confirms the gates support variational algorithms without prohibitive overhead.

Engineering advances here—particularly the crosstalk model and calibration routine—translate quantum information requirements into concrete hardware constraints that other platforms can adopt. Remaining limitations include the need for longer coherence times and deterministic coupling to additional communication qubits. A natural strengthening would be a 10-qubit register with real-time feedback, which would test whether the same optimization scales without fidelity loss.