Two-qubit correlated quantum dephasometry of altermagnets

Collective atom-light interactions have received considerable attention due to their applications in quantum metrology. The dissipative collective emission processes (e.g., superradiance) originate from interactions with EM modes in resonance with atoms and have received much interest. Meanwhile, the analogous non-dissipative collective dephasing phenomena mediated by EM environments remain less explored. In this talk, we will first introduce the nanophotonic collective dephasing phenomenon arising from spatially correlated fluctuations in photonic environments near materials. We show that collective dephasing in this nanophotonic environment is enhanced by over 10 orders of magnitude compared to free space or cavities, which leads to collectively accelerated or suppressed dephasing in entangled states without photon emission. We then reveal that quantum sensing based on two-qubit collective dephasing can exhibit enhanced sensitivity to momentum space anisotropy in material response compared to single-qubit dephasing. As an example, we apply the two-qubit correlated dephasometry to probe 2D altermagnets by exploiting symmetry-linked anisotropies in the noise correlation kernel. Our results demonstrate correlated dephasing of quantum sensors in the near field as a metrological resource, enabling momentum-resolved quantum noise spectroscopy for unconventional magnetic and superconducting order.