Interfacial electron-hole coexistence and ultrathin superconductivity in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>La</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi>CuO</mml:mi> <mml:mn>4</mml

We present a comprehensive transport study of interface superconductivity in ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}/{\mathrm{LaSrCuO}}_{4}$ [LCO/LSCO(1.0)] bilayers, where both constituent layers are insulating in bulk. Our experiments reveal that superconductivity is localized within the LCO layer, with holes exhibiting a decaying distribution that extends up to 5 unit cells, reaching optimal superconductivity at the third ${\mathrm{CuO}}_{2}$ plane. Furthermore, Hall effect measurements indicate a mobile electron layer in LSCO(1.0), suggesting a unique coexistence of electrons and holes at the interface. Superconductivity persists in bilayers with total thickness as thin as 1.5 unit cells. These results provide insights into charge-carrier dynamics at cuprate interfaces and demonstrate robust interfacial superconductivity down to the ultrathin limit.