We propose a strategy to enhance dielectric permittivity by tuning local electronic structures, exemplified by Nb-doped rutile-type $\mathrm{Ti}{\mathrm{O}}_2$. Substituting only 0.5% of ${\mathrm{Ti}}^{4+}$ with $\mathrm{N}{\mathrm{b}}^{5+}$ increases the relative permittivity by ∼1200—fivefold higher than that of pristine $\mathrm{Ti}{\mathrm{O}}_2$—while maintaining low dielectric loss (tan δ ∼ 0.02) at cryogenic temperatures. First-principles calculations reveal that excess electrons introduced by Nb substitution localize between Nb and adjacent Ti ions, forming molecular polarons with intrinsic electric dipole moments. These polarons undergo quantum tunneling–assisted flip-flop hopping between their first-nearest-neighbor Ti sites, allowing field-induced dipole reorientation even at 4.2 K. This mechanism explains the persistence of high permittivity at cryogenic temperatures, where classical hopping and Maxwell–Wagner–Sillars effects become negligible, and provides a microscopic explanation for the saturation observed at higher Nb concentrations because of Nb–Nb dimer formation and polaron trapping. Our findings establish a design framework for quantum-enhanced dielectrics based on local correlations and tunneling dynamics in simple oxides.

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• Capacitance
• Charge dynamics
• Dielectric properties
• Dopants
• Electric polarization
• Electrical properties
• Hopping transport
• Local density of states
• Permittivity
• Point defects
• Polarons
• First-principles calculations