High-fidelity gates in a multi-qubit diamond quantum processor (Part II, Circuit design and Benchmarking)

Spins associated to solid-state color centers might enable a range of quantum technologies. Recent progress using the nitrogen-vacancy center in diamond include the fault-tolerant operation of a logical qubit and the creation of entanglement on a metropolitan scale. It remains a key challenge to obtain high-fidelity gates on the defect center’s electron spin and multiple surrounding nuclear spins [1, 2].



In this project, we use Gate Set Tomography (GST) to demonstrate two-qubit gate fidelities over 99% in a multi-qubit processor. Next, we use the detailed knowledge of interactions in our system to make a multi-qubit circuit design that preserves qubit coherence and avoids qubit-qubit crosstalk. The circuit design allows for exploring different (QCVV) methods of processor-scale benchmarking which reveal crosstalk emerging only when employing several qubits at the same time. These results provide a path towards reliable multi-qubit quantum processors based on color centers in diamond and other materials.



[1] Bartling et al. Universal high-fidelity quantum gates for spin-qubits in diamond. arXiv:2403.10633 (2024)

[2] Van Ommen et al. Improved Electron-Nuclear Quantum Gates for Spin Sensing and Control. arXiv:2409.13610 (2024)