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

Decoherence and dephasing in coupled Josephson-junction qubits

Michele Governale, Milena Grifoni, Gerd Schön

arXiv:cond-mat/0104023Chemical PhysicsJun 1, 200159 citations

Decoherence and dephasing in coupled Josephson-junction qubits

Michele Governale, Milena Grifoni, Gerd Schön

May 15, 200160 citations

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

Decoherence of Josephson charge qubit

Xian-Ting Liang

arXiv:quant-ph/0506044Physica C SuperconductivityJun 11, 20067 citations

Superconducting phase qubit based on the Josephson oscillator with strong anharmonicity

Alexander B Zorin, F. Chiarello

We propose a superconducting phase qubit on the basis of the radio-frequency superconducting quantum interference device with the screening parameter value ${\ensuremath{\beta}}_{L}\ensuremath{\equiv}(2\ensuremath{\pi}/{\ensuremath{\Phi}}_{0})L{I}_{c}\ensuremath{\approx}1$, biased by a half-flux quantum ${\ensuremath{\Phi}}_{e}={\ensuremath{\Phi}}_{0}/2$. Significant anharmonicity $(>30%)$ can be achieved in this system due to the interplay of the cosine Josephson potential and the parabolic magnetic energy potential that ultimately leads to the quartic polynomial shape of the well. The two lowest eigenstates in this global minimum perfectly suit for the qubit which is insensitive to the charge variable, biased in the optimal point and allows an efficient dispersive readout. Moreover, the transition frequency in this qubit can be tuned within an appreciable range allowing variable qubit-qubit coupling.We propose a superconducting phase qubit on the basis of the radio-frequency superconducting quantum interference device with the screening parameter value ${\ensuremath{\beta}}_{L}\ensuremath{\equiv}(2\ensuremath{\pi}/{\ensuremath{\Phi}}_{0})L{I}_{c}\ensuremath{\approx}1$, biased by a half-flux quantum ${\ensuremath{\Phi}}_{e}={\ensuremath{\Phi}}_{0}/2$. Significant anharmonicity $(>30%)$ can be achieved in this system due to the interplay of the cosine Josephson potential and the parabolic magnetic energy potential that ultimately leads to the quartic polynomial shape of the well. The two lowest eigenstates in this global minimum perfectly suit for the qubit which is insensitive to the charge variable, biased in the optimal point and allows an efficient dispersive readout. Moreover, the transition frequency in this qubit can be tuned within an appreciable range allowing variable qubit-qubit coupling.

arXiv:0908.3937Physical Review BDec 30, 200914 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.

(>30%)

can be achieved in this system due to the interplay of the cosine Josephson potential and the parabolic magnetic energy potential that ultimately leads to the quartic polynomial shape of the well. The two lowest eigenstates in this global minimum perfectly suit for the qubit which is insensitive to the charge variable, biased in the optimal point and allows an efficient dispersive readout. Moreover, the transition frequency in this qubit can be tuned within an appreciable range allowing variable qubit-qubit coupling.