HH Vallabhapurapu, I Hansen, C Adambukulam, R Stöhr, A Denisenko, CH Yang, A Laucht
A practical implementation of a quantum computer requires robust qubits that are protected against their noisy environment. Dynamical decoupling techniques have been successfully used in the past to offer protected high-fidelity gate operations in negatively charged nitrogen-vacancy (NV) centers in diamond, albeit under specific conditions with the intrinsic nitrogen nuclear spin initialized. In this work, we show how the sinusoidally modulated, always rotating, and tailored (SMART) protocol, an extension of the dressed-qubit concept, can be implemented for continuous protection to offer Clifford gate fidelities compatible with fault-tolerant schemes, whilst prolonging the coherence time of a single NV qubit at room temperature. We show an improvement in the average Clifford gate fidelity from 0.940±0.005 for the bare qubit to 0.993±0.002 for the SMART qubit, with the nitrogen nuclear spin in a random orientation. We further show a 30 times improvement in the qubit T2 coherence times compared to the bare qubit.