Fig. 1

(a) The schematic diagram of spin qubit symmetrically coupled to the critical spin environment described as a transverse field Ising chain. When the magnetic field is large (\(|h(t)| > 1\)), (right and left panels), the environment is in a paramagnetic phase, where spins aligned with the field. In contrast, when the field is small (\(|h(t)| < 1\); (center panel), the spin chin enters a ferromagnetic phase, where spins ordered in x or \(-x\) direction. (b) The decoherence factor can be directly measured through a Ramsey experiment, which involves a \(\pi /2\) pulse sequence followed by a projective measurement in the Z-basis on the central qubit^47,48,49,50.