We have designed and experimentally implemented a circuit of inductively coupled superconducting charge qubits, where a Josephson junction is used as an inductance, and the coupling between the qubits is controlled by an applied magnetic flux. Spectroscopic measurements on the circuit are in good agreement with theoretical calculations. We observed anticrossings which originate from the coupling between the qubit and the plasma mode of the Josephson junction. Moreover, the size of the anticrossing depends on the external magnetic flux, which demonstrates the controllability of the coupling.We have designed and experimentally implemented a circuit of inductively coupled superconducting charge qubits, where a Josephson junction is used as an inductance, and the coupling between the qubits is controlled by an applied magnetic flux. Spectroscopic measurements on the circuit are in good agreement with theoretical calculations. We observed anticrossings which originate from the coupling between the qubit and the plasma mode of the Josephson junction. Moreover, the size of the anticrossing depends on the external magnetic flux, which demonstrates the controllability of the coupling.

arXiv:0802.0353Physical Review BFeb 11, 200828 citations

Josephson charge-phase qubit with radio frequency readout: Coupling and decoherence

Alexander B Zorin

The Josephson qubit based on a superconducting single charge transistor inserted in a low-inductance superconducting loop is considered. The loop is inductively coupled to a radio-frequency driven tank circuit enabling the readout of the qubit states by measuring the effective Josephson inductance of the transistor. The effect of qubit dephasing and relaxation due to electric and magnetic control lines, as well as the measuring system, is evaluated. Recommendations for qubit operation with minimum decoherence are given.The Josephson qubit based on a superconducting single charge transistor inserted in a low-inductance superconducting loop is considered. The loop is inductively coupled to a radio-frequency driven tank circuit enabling the readout of the qubit states by measuring the effective Josephson inductance of the transistor. The effect of qubit dephasing and relaxation due to electric and magnetic control lines, as well as the measuring system, is evaluated. Recommendations for qubit operation with minimum decoherence are given.

arXiv:cond-mat/0312225Journal of Experimental and Theoretical PhysicsJun 1, 200421 citations

Current-Controlled coupling of superconducting charge qubits

Margareta Wallquist, J. Lantz, Vitaly S. Shumeiko +1 more

Springer eBooksMay 29, 20061 citation

Ground-state characterization of Nb charge-phase Josephson qubits

H. Zangerle, Jens Könemann, Brigitte Mackrodt +5 more

We present investigations of Josephson charge-phase qubits of superconducting quantum interference device (SQUID) configuration, inductively coupled to a radio-frequency-driven tank circuit, enabling the readout of the states by measuring the Josephson inductance of the qubit. The circuits, including junctions with linear dimensions of $60\phantom{\rule{0.3em}{0ex}}\mathrm{nm}\ifmmode\times\else\texttimes\fi{}60\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and $80\phantom{\rule{0.3em}{0ex}}\mathrm{nm}\ifmmode\times\else\texttimes\fi{}80\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, are fabricated from $\mathrm{Nb}∕\mathrm{Al}{\mathrm{O}}_{x}∕\mathrm{Nb}$ trilayer and allow the determination of relevant sample parameters at liquid helium temperature. The observed partial suppression of the circulating supercurrent in the qubit loop at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is explained within the framework of a quantum-statistical model. We have probed the ground-state properties of qubit structures with different ratios of the Josephson coupling to Coulomb charging energy at $20\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ , demonstrating both the magnetic control of phase and the electrostatic control of charge of the qubit.We present investigations of Josephson charge-phase qubits of superconducting quantum interference device (SQUID) configuration, inductively coupled to a radio-frequency-driven tank circuit, enabling the readout of the states by measuring the Josephson inductance of the qubit. The circuits, including junctions with linear dimensions of $60\phantom{\rule{0.3em}{0ex}}\mathrm{nm}\ifmmode\times\else\texttimes\fi{}60\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and $80\phantom{\rule{0.3em}{0ex}}\mathrm{nm}\ifmmode\times\else\texttimes\fi{}80\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, are fabricated from $\mathrm{Nb}∕\mathrm{Al}{\mathrm{O}}_{x}∕\mathrm{Nb}$ trilayer and allow the determination of relevant sample parameters at liquid helium temperature. The observed partial suppression of the circulating supercurrent in the qubit loop at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is explained within the framework of a quantum-statistical model. We have probed the ground-state properties of qubit structures with different ratios of the Josephson coupling to Coulomb charging energy at $20\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$, demonstrating both the magnetic control of phase and the electrostatic control of charge of the qubit.

arXiv:cond-mat/0601199Physical Review BJun 28, 20069 citations

\mathrm{Nb}∕\mathrm{Al}{\mathrm{O}}_{x}∕\mathrm{Nb}

trilayer and allow the determination of relevant sample parameters at liquid helium temperature. The observed partial suppression of the circulating supercurrent in the qubit loop at

4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}

is explained within the framework of a quantum-statistical model. We have probed the ground-state properties of qubit structures with different ratios of the Josephson coupling to Coulomb charging energy at

20\phantom{\rule{0.3em}{0ex}}\mathrm{mK}

, demonstrating both the magnetic control of phase and the electrostatic control of charge of the qubit.