Quantum interference of tunneling paths under a double-well barrier

The tunnel effect, a hallmark of the quantum realm, involves motion across a classically forbidden region. In a driven nonlinear system, two or more tunneling paths may coherently interfere, enhancing or cancelling the tunnel effect. Since individual quantum systems are difficult to control, this interference effect has only been studied for the lowest energy states of many-body ensembles. In our experiment, we show a coherent cancellation of the tunneling amplitude in the ground and excited state manifold of an individual squeeze-driven Kerr oscillator, a consequence of the destructive interference of tunneling paths in the classically forbidden region. The tunnel splitting vanishes periodically in the spectrum as a function of the frequency of the squeeze-drive, with the periodicity given by twice the Kerr coefficient. This resonant cancellation, combined with an overall exponential reduction of tunneling as a function of both amplitude and frequency of the squeeze-drive, reduces drastically the well-switching rate under incoherent environment-induced evolution. The control of tunneling via interference effects can be applied to quantum computation, molecular, and nuclear physics.