Entanglement and so-called magic states have long been viewed as the key resources for quantum error correction. Now contextuality, a hallmark of quantum theory, joins them as a complementary resource.
Machines make mistakes, and as they scale up, so too do the opportunities for error. Quantum computers are no exception; in fact, their errors are especially frequent and difficult to control. This fragility has long been a central obstacle to building large-scale devices capable of practical, universal quantum computation. Quantum error correction attempts to circumvent this obstacle, not by eliminating sources of error but by encoding quantum information in such a way that errors can be detected and corrected as they occur [1]. In doing so, the approach enables fault-tolerant quantum computation. Over the past few decades, researchers have learned that this robustness relies on intrinsically quantum resources, most notably, entanglement [2] and, more recently, so-called magic states [3].









