Electronically-tunable quantum phase slips in voltage-biased superconducting rings

Superconducting qubits hinge on the coherent tunneling of Cooper pairs across the insulating barrier of a Josephson junction, two superconducting electrodes separated by an insulating barrier. For example, in a superconducting loop interrupted by a thin insulator, the Cooper-pair tunneling coherently couples the macroscopic flux states of the loop, giving rise to the simplest implementation of a flux qubit, the rf SQUID. Likewise, the superconducting loop can be interrupted by a nanowire where, due to its small cross-sectional area, quantum-phase-slip rates in the gigahertz regime can be achieved, giving rise to a phase-slip flux qubit. Here, we present the use of a bias voltage across a superconducting loop to electrostatically induce a weak link, thereby enhancing the rate of quantum phase slips without physically interrupting the loop. Our Ginzburg-Landau simulations show that the bias voltage modulates the energy barrier separating the adjacent flux states of the loop, suggesting a route towards a phase-slip flux qubit whose transition frequency is electronically tunable.