Enhanced solid-state multispin metrology using dynamical decoupling

We use multipulse dynamical decoupling to increase the coherence lifetime (T₂) of large numbers of nitrogen-vacancy (NV) electronic spins in room temperature diamond, thus enabling scalable applications of multispin quantum information processing and metrology. We realize an order-of-magnitude extension of the NV multispin T₂ in three diamond samples with widely differing spin impurity environments. In particular, for samples with nitrogen impurity concentration 1 ppm, we extend T₂ to $>$2 ms, comparable to the longest coherence time reported for single NV centers, and demonstrate a tenfold enhancement in NV multispin sensing of ac magnetic fields.