Proximate deconfined quantum critical point in SrCu 2 ( BO 3 ) 2 .

The deconfined quantum critical point (DQCP) represents a paradigm shift in quantum matter studies, presenting a "beyond Landau" scenario for order-order transitions. Its experimental realization, however, has remained elusive. Using high-pressure 11 B nuclear magnetic resonance measurements on the quantum magnet SrCu[Formula: see text](BO[Formula: see text])[Formula: see text], we here demonstrate a magnetic-field induced plaquette-singlet to antiferromagnetic transition above [Formula: see text] GPa at a notably low temperature, [Formula: see text]K. First-order signatures of the transition weaken with increasing pressure, and we observe quantum critical scaling at the highest pressure, [Formula: see text] GPa. Supported by model calculations, we suggest that these observations can be explained by a proximate DQCP inducing critical quantum fluctuations and emergent O(3) symmetry of the order parameters. Our findings offer a concrete experimental platform for the investigation of the DQCP.