A tipping pulse scheme for a rf-SQUID qubit

We present a technique to control the quantum state of a rf-SQUID qubit, We propose to employ a stream of single flux quantum (SFQ) pulses magneticall y coupled to the qubit junction to momentarily suppress its critical curren t. This effectively lowers the barrier in the double-well rf SQUID potentia l thereby increasing the tunneling oscillation frequency between the wells. By carefully choosing the time interval between SFQ pulses one may acceler ate the interwell tunneling rate. Thus it is possible to place the qubit in to a chosen superposition of flux states and then effectively to freeze the qubit state. We present both numerical simulations and analytical time-dep endent perturbation theory calculations that demonstrate the technique. Usi ng this strategy one may control the quantum state of the rf SQUID in a way analogous to the x pulses in other qubit schemes.