Dynamically modulated light-matter coupling for Bosonic Fault Tolerance

Superconducting resonators have emerged as a prominent platform for studying bosonic physics, offering universal control and measurement through strong couplings to ancillary qubits. However, both control and error correction in these systems are fundamentally limited by the coherence of the ancilla qubits, which introduce errors like dephasing and Kerr evolution when idle, and propagate errors to the bosonic mode when entangled with them. In this work, we break this fundamental trade-off between control and error propagation by introducing a special parametric coupler between the qubit and the oscillator. When idle, this 'Linear INductive Coupler' (LINC), offers a linear environment to the oscillator and statically decouples it from the qubit. To turn on the oscillator control, we dress the oscillator-qubit system dynamically with an off-resonant parametric beamsplitter, with pulses modulating freely between the dressed and undressed frames on a timescale of < 100 ns. This allows a dynamic exploration of the rich physics of the straddling regime, including moving from positive to negative dispersive shifts within a single pulse, and engineering symmetries in the qubit-oscillator coupling that prevent the propagation of qubit errors to the oscillator even when entangled. This allows significant improvements in continuous variable simulation and error-correction.