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We introduce a technique to control the macroscopic quantum state of an rf SQUID qubit. We propose to employ a stream of single flux quantum (SFQ) pulses magnetically coupled to the qubit junction to momentarily suppresses its critical current. This effectively lowers the barrier in the double-well rf-SQUID potential thereby increasing the tunneling oscillation frequency between the wells. By carefully choosing the time interval between SFQ pulses one may accelerate the interwell tunneling rate. Thus it is possible to place the qubit into a chosen superposition of flux states and then effectively to freeze the qubit state. We present both numerical simulations and analytical time-dependent perturbation theory calculations that demonstrate the technique. Using this strategy one may control the quantum state of the rf-SQUID in a way analogous to the pi pulses in other qubit schemes. Research supported in part by ARO grant # DAAG55-98-1-0367.
A practical strategy for synchronizing the properties of compound Josephson junction rf-SQUID qubits on a multiqubit chip has been demonstrated. The impacts of small ($sim1%$) fabrication variations in qubit inductance and critical current can be min
We propose a new approach for the arbitrary rotation of a three-level SQUID qubit and describe a new strategy for the creation of coherence transfer and entangled states between two three-level SQUID qubits. The former is succeeded by exploring the c
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We believe that the best chance to observe macroscopic quantum coherence (MQC) in a rf-SQUID qubit is to use on-chip RSFQ digital circuits for preparing, evolving and reading out the qubits quantum state. This approach allows experiments to be conduc
The superconducting fluxonium circuit is an RF-SQUID-type flux qubit that uses a large inductance built from an array of Josephson junctions or a high kinetic inductance material. This inductance suppresses charge sensitivity exponentially and flux s