Dr Matthias Müller

Toward a Scalable Diamond-based Spin-Qubit Register

Diamond-based quantum technology is a fast-emerging field with both scientific and technological importance. The nuclear spins in the solid-state diamond crystalline structure allow for a room-temperature qubit register with a star topology around the central electron of the nitrogen-vacancy (NV) center. Entangling gates between such spin registers are the key challenge toward scalable architectures. Entanglement between dipolar-coupled NV spin pairs has been demonstrated, but with a limited entanglement fidelity and its error sources have not been characterized. Here, I present the recent experimental achievement of such a two-qubit gate between two NV centers and a theoretical analysis of the further potential, including with tools for benchmarking and quantum optimal control [2,3,4]. By tuning the relevant parameters and the application of decoupling sequences, we managed to design a robust and simple entangling gate between two NV centers. We quantified the influence of multiple error sources on the gate performance. Experimentally, this resulted in a gate fidelity of (96 pm 2.5)% at room temperature. Our identification of the dominant errors paves the way towards NV-NV gates beyond the error correction threshold. [1] T. Joas et al., arXiv:2406.04199 (2024) [2] P. Vetter et al. arXiv:2403.00616 (2024) [3] P. Rembold et al., AVS Quantum Sci. 2, 024701 (2020) [4] M. Rossignolo et al. Comp. Phys. Comm. 291, 108782 (2023)