The strongly correlated two-dimensional electron liquid within ${\mathrm{SmTiO}}_3/{\mathrm{SrTiO}}_3/{\mathrm{SmTiO}}_3$ quantum well structures exhibits a pseudogap phase when the quantum well width is sufficiently narrow. Using low-temperature transport and optical experiments that drive the quantum-well system out of equilibrium, we find evidence of mobile, long-lived, negatively charged quasiparticles, consistent with the idea that the pseudogap phase arises from strongly bound electron pairs. These experimental results establish a connection between quantum confinement and enhanced electron pairing, which may provide a pathway to higher-temperature superconductors.

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• Electrical properties
• Pseudogap
• Superconducting fluctuations
• Superconducting gap
• Complex oxides
• Low-temperature superconductors
• Quantum wells
• Strongly correlated systems