Small superconducting islands can exhibit charge quantization, where Coulomb interactions compete with Cooper pairing. Using scanning tunneling spectroscopy, we probe this interplay by measuring the charging energy ($E_C$) and the pairing energy ($\mathrm{\Delta }$) of individual Pb nanoislands. Below a critical island size, where $E_C>\mathrm{\Delta }$, we observe a crossover between even and odd parity ground states. By applying controlled voltage pulses, we continuously tune the island’s electrostatic potential and map the full charge-parity landscape. These results demonstrate tunable superconducting ground states, offering a potential platform for qubit design and control.

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• Coulomb blockade
• Superconductivity
• Quantum many-body systems
• Parity
• Scanning tunneling spectroscopy