<p>Graphene enables precise carrier-density control via gating, making it an ideal platform for studying electronic interactions. However, sample inhomogeneities often limit access to the low-density regimes where these interactions dominate. Enhancing carrier mobility is therefore crucial for exploring fundamental properties and developing device applications. Here, we demonstrate a significant reduction in external inhomogeneity using a double-layer graphene architecture separated by an ultra-thin hexagonal boron nitride layer. Mutual screening between the layers reduces scattering from random Coulomb potentials, resulting in a quantum mobility exceeding <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(1{0}^{7}{{\rm{c}}}{{{\rm{m}}}}^{2}{{{\rm{V}}}}^{-1}{{{\rm{s}}}}^{-1}\)</EquationSource> <EquationSource Format="MATHML"><math> <mn>1</mn> <msup> <mrow> <mn>0</mn> </mrow> <mrow> <mn>7</mn> </mrow> </msup> <mi mathvariant="normal">c</mi> <msup> <mrow> <mi mathvariant="normal">m</mi> </mrow> <mrow> <mn>2</mn> </mrow> </msup> <msup> <mrow> <mi mathvariant="normal">V</mi> </mrow> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> <msup> <mrow> <mi mathvariant="normal">s</mi> </mrow> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </math></EquationSource> </InlineEquation>. Shubnikov–de Haas oscillations emerge at magnetic fields below 1 mT, while integer quantum Hall features are observed at 0.002 T. Furthermore, we identify a fractional quantum Hall plateau at a filling factor of <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({v}_{{{\rm{tot}}}}=-10/3\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mi>v</mi> </mrow> <mrow> <mi mathvariant="normal">tot</mi> </mrow> </msub> <mo>=</mo> <mo>−</mo> <mn>10</mn> <mo>/</mo> <mn>3</mn> </math></EquationSource> </InlineEquation> at 2 T. These results demonstrate the platform’s suitability for investigating strongly correlated electronic phases in graphene-based heterostructures.</p>