Electrically-tunable phase-slip qubits

The simplest form of a flux qubit is constructed by interrupting a superconducting loop (e.g., a ring) with an insulating barrier, thus forming a Josephson junction. The tunneling of Cooper pairs across the insulating barrier allows for a coherent coupling of two macroscopic flux states with oppositely circulating currents. In a similar manner, one can interrupt the superconducting loop with a nanowire over which superconducting vortices are coherently exchanged, a mechanism referred to as quantum phase slips (QPSs), giving rise to phase-slip qubits. Here, we investigate the possibility of using a voltage-biased superconducting ring to realize a phase-slip qubit. Using time-dependent Ginzburg-Landau equations, we show that the bias voltage modulates the free energy barrier between subsequent flux states of the ring. For a small but non-zero barrier, we calculate the rate of QPSs as a function of bias voltage, and investigate the possibility of realizing electrically-tunable phase-slip qubits.