Transmon Qubit: Josephson Washboard Potential

A transmon — the workhorse qubit of Google, IBM and Rigetti's processors — is a single Josephson junction shunted by a capacitor, sitting in the "washboard" potential U(φ) = −E_J cos φ. This simulator renders that trough in 3D, overlays its quantized, unevenly-spaced energy levels, and animates a classical phase particle whose oscillation frequency reproduces the qubit's f₀₁. Tune the E_J/E_C ratio to move between the charge-sensitive Cooper-pair-box regime and the transmon sweet spot, or sweep an external flux through a SQUID loop to watch the qubit frequency collapse toward zero at half a flux quantum, exactly as it does on real flux-tunable hardware.