Switching time of a double barrier josephson junction based qubit gate

The switching dynamics of a double-barrier Josephson junction is analyzed as a function of the microscopic properties of its electrodes. In particular, it is found that the nonstationary behavior of the Josephson phase difference is very sensitive to dissipation mechanisms acting inside the intrinsic shunt. The leading factor that determines the dissipation is the local electron density of states N(E) inside the electrodes. The roles of junction geometry, electrode purity, and interface quality are discussed and how they affect the details of N(E), hence the resulting phase dynamics. The microscopic analyses allow optimization of the performance of double-barrier Josephson junction-based rapid-single-flux-quantum circuits in two ways: 1) decreasing the switching time of Josephson elements and 2) reducing the excess wiring. Such an analysis is facilitated with the aid of a lumped circuit representation which generalizes the nonlinear resistive-shunted-junction model.The switching dynamics of a double-barrier Josephson junction is analyzed as a function of the microscopic properties of its electrodes. In particular, it is found that the nonstationary behavior of the Josephson phase difference is very sensitive to dissipation mechanisms acting inside the intrinsic shunt. The leading factor that determines the dissipation is the local electron density of states N(E) inside the electrodes. The roles of junction geometry, electrode purity, and interface quality are discussed and how they affect the details of N(E), hence the resulting phase dynamics. The microscopic analyses allow optimization of the performance of double-barrier Josephson junction-based rapid-single-flux-quantum circuits in two ways: 1) decreasing the switching time of Josephson elements and 2) reducing the excess wiring. Such an analysis is facilitated with the aid of a lumped circuit representation which generalizes the nonlinear resistive-shunted-junction model.

IEEE Transactions on Applied SuperconductivityMar 1, 20043 citations

Two-qubit gate based on a multiterminal double-barrier Josephson junction

Serhii E. Shafranjuk

A multiterminal double-barrier SISIS junction (S and I denote a superconductor and an insulating barrier, respectively) is suggested as a two-qubit gate with tunable intrinsic coupling. Two quantum wells are formed in the vicinities of the left and right SIS subjunctions. This gives two individual qubits, which are intrinsically coupled via the middle S layer due to phase coherence. The interqubit coupling $J$ is tuned by two bias supercurrents ${I}_{1}$ and ${I}_{2}$ across each of the SIS subjunctions independently. Additional coupling is accomplished by transport supercurrents ${I}_{l}^{\mathrm{tr}}$ along adjacent S layers. Using a microscopic model we compute major qubit characteristics and study sources of the intrinsic decoherence. We compute the entanglement of the two-qubit states, leakage and fidelity characteristics versus $J$ , and discuss the readout process.A multiterminal double-barrier SISIS junction (S and I denote a superconductor and an insulating barrier, respectively) is suggested as a two-qubit gate with tunable intrinsic coupling. Two quantum wells are formed in the vicinities of the left and right SIS subjunctions. This gives two individual qubits, which are intrinsically coupled via the middle S layer due to phase coherence. The interqubit coupling $J$ is tuned by two bias supercurrents ${I}_{1}$ and ${I}_{2}$ across each of the SIS subjunctions independently. Additional coupling is accomplished by transport supercurrents ${I}_{l}^{\mathrm{tr}}$ along adjacent S layers. Using a microscopic model we compute major qubit characteristics and study sources of the intrinsic decoherence. We compute the entanglement of the two-qubit states, leakage and fidelity characteristics versus $J$, and discuss the readout process.

Physical Review BJul 26, 20069 citations

J

is tuned by two bias supercurrents

{I}_{1}

and

{I}_{2}

across each of the SIS subjunctions independently. Additional coupling is accomplished by transport supercurrents

{I}_{l}^{\mathrm{tr}}

along adjacent S layers. Using a microscopic model we compute major qubit characteristics and study sources of the intrinsic decoherence. We compute the entanglement of the two-qubit states, leakage and fidelity characteristics versus

J

, and discuss the readout process.