Understanding and protecting the coherence of individual quantum systems is a central challenge in quantum science and technology. Over the past decades, a rich variety of methods to extend coherence have been developed. A complementary approach is to look for naturally occurring systems that are inherently protected against decoherence. Here, we show that pairs of identical nuclear spins in solids form intrinsically long-lived qubits. We study three carbon-13 pairs in diamond and realize high-fidelity measurements of their quantum states using a single nitrogen-vacancy center in their vicinity. We then reveal that the spin pairs are robust to external perturbations due to a combination of three phenomena: a decoherence-free subspace, a clock transition, and a variant on motional narrowing. The resulting inhomogeneous dephasing time is T2∗=1.9(3) min, the longest reported for individually controlled qubits. Finally, we develop complete control and realize an entangled state between two spin pairs through projective parity measurements. These long-lived qubits are abundantly present in diamond and other solids and provide new opportunities for ancilla-enhanced quantum sensing and for robust memory qubits for quantum networks.
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Bartling, H. P. (Creator), Abobeih, M. H. M. A. (Creator), Pingault, B. J. (Creator), Degen, M. J. (Creator), Loenen, S. J. H. (Creator), Bradley, C. E. (Creator), Randall, J. A. D. (Creator), Markham, M. (Creator), Twitchen, D. J. (Creator) & Taminiau, T. H. (Creator), TU Delft - 4TU.ResearchData, 21 Apr 2023