The Heavy Chain Protects The Flux
The Heavy Chain Protects The Flux
To protect a superconducting qubit from noise, you must anchor it. The transmon achieves this by shunting a delicate Josephson junction with a massive capacitor, drowning out charge noise at the cost of flattening its energy levels and weakening its computational speed.
The fluxonium qubit takes a different path. It abandons the capacitor and instead shunts the computational junction with a massive inductor.
But a standard wire cannot provide enough inductance without becoming physically huge and acting as an antenna for stray radiation. Instead, the fluxonium builds a "super-inductor" out of a chain of over a hundred larger, specialized Josephson junctions.
This heavy chain of junctions acts as a pure, enormous inductance. It securely anchors the quantum phase across the computational junction, protecting the flux state from low-frequency noise while preserving the sharp, distinct energy levels needed for fast, high-fidelity quantum logic. The delicate state is suspended by the sheer weight of the chain.