Drive-Only Interaction Engineering via Dynamical Freezing

Freezing is usually used to suppress unwanted dynamics, but it can also be used to engineer interactions. We introduce freezing-induced interaction engineering, a drive-only control paradigm in which dynamically freezing an auxiliary subsystem reshapes the effective Hamiltonian of the remaining degrees of freedom. As a concrete realization, we consider a three-qubit architecture where a driven modulator M is coupled to one of two target qubits, Q₁, while Q₁ and Q₂ retain a fixed native exchange-type interaction. When M is frozen in a dressed eigenstate, its projection renormalizes the local Hamiltonian of Q₁. This makes the dressed-frame detuning between Q₁ and Q₂ controllable by the drive frequency. The native interaction can then be switched between two regimes: an interaction-off regime with large dressed-frame detuning, and an interaction-on regime with resonant exchange. In the interaction-on regime, the protocol realizes an iSWAP gate using the native Q_1Q2 coupling. Full lab-frame simulations show high-fidelity iSWAP dynamics and strong interaction suppression in the interaction-off regime. By combining native-coupling gate speed with drive-only operational simplicity, freezing-induced interaction engineering provides a route toward fast, drive-controlled entangling gates in fixed-frequency quantum architectures.