We present results on a circuit QED experiment in which a separate transmission line is used to address a quasilumped element superconducting microwave resonator which is in turn coupled to an $\mathrm{Al}/{\mathrm{AlO}}_{x}/\mathrm{Al}$ Cooper-pair box charge qubit. With our device, we find a strong correlation between the lifetime of the qubit and the inverse of the coupling between the qubit and the transmission line. At the smallest coupling we measured, the lifetime of the Cooper-pair box was ${T}_{1}=200\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$, which represents more than a twentyfold improvement in the lifetime of the Cooper-pair box compared with previous results. These results imply that the loss tangent in the ${\mathrm{AlO}}_{x}$ junction barrier must be less than about $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ at 4.5 GHz, about 4 orders of magnitude less than reported in larger area $\mathrm{Al}/{\mathrm{AlO}}_{x}/\mathrm{Al}$ tunnel junctions.We present results on a circuit QED experiment in which a separate transmission line is used to address a quasilumped element superconducting microwave resonator which is in turn coupled to an $\mathrm{Al}/{\mathrm{AlO}}_{x}/\mathrm{Al}$ Cooper-pair box charge qubit. With our device, we find a strong correlation between the lifetime of the qubit and the inverse of the coupling between the qubit and the transmission line. At the smallest coupling we measured, the lifetime of the Cooper-pair box was ${T}_{1}=200\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$, which represents more than a twentyfold improvement in the lifetime of the Cooper-pair box compared with previous results. These results imply that the loss tangent in the ${\mathrm{AlO}}_{x}$ junction barrier must be less than about $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ at 4.5 GHz, about 4 orders of magnitude less than reported in larger area $\mathrm{Al}/{\mathrm{AlO}}_{x}/\mathrm{Al}$ tunnel junctions.

arXiv:1101.4692Physical Review LettersMar 22, 201170 citations

Entangling phase qubits via a common transmission line cavity

Jae Hyung Park, Raymond W. Simmonds

Bulletin of the American Physical SocietyMar 12, 20080 citations

The influence of dissipation in a 1D quantum metamaterial

R D Wilson, M. J. Everitt, Sergey E. Savel'ev +1 more

Quantum metamaterials consist of quantum coherent structures made up of artificial atoms connected by a transmission medium. In this work we investigate the effects of decoherence in both the transmission medium and the artificial atom using a fully quantum mechanical model. We consider a prototypical solid state 1D quantum metamaterial, i.e. a superconducting flux qubit coupled to a transmission line section on resonance. An initially excited qubit is found to effectively pump a propagating coherent pulse and increase the average output power of the transmission line. Evidence of entanglement between the qubit and the transmission line with a propagating coherent pulse is also demonstrated. This signature behaviour is found to still be evident when a level of decoherence in line with that found in typical experiments is introduced into the transmission line section as well as the qubit. Increasing levels of decoherence, particularly in the qubit, are shown to be dangerous as they destroy the quantum correlations between the qubit and the propagating field.Quantum metamaterials consist of quantum coherent structures made up of artificial atoms connected by a transmission medium. In this work we investigate the effects of decoherence in both the transmission medium and the artificial atom using a fully quantum mechanical model. We consider a prototypical solid state 1D quantum metamaterial, i.e. a superconducting flux qubit coupled to a transmission line section on resonance. An initially excited qubit is found to effectively pump a propagating coherent pulse and increase the average output power of the transmission line. Evidence of entanglement between the qubit and the transmission line with a propagating coherent pulse is also demonstrated. This signature behaviour is found to still be evident when a level of decoherence in line with that found in typical experiments is introduced into the transmission line section as well as the qubit. Increasing levels of decoherence, particularly in the qubit, are shown to be dangerous as they destroy the quantum correlations between the qubit and the propagating field.

Superconductor Science and TechnologyJul 2, 20133 citations

Quantum simulation using superconducting qubits coupled to a 1D transmission line

Daniel Campbell, Philip Krantz, Fei Yan +4 more

Bulletin of the American Physical SocietyMar 14, 20170 citations

We present results on a circuit QED experiment in which a separate transmission line is used to address a quasilumped element superconducting microwave resonator which is in turn coupled to an

\mathrm{Al}/{\mathrm{AlO}}_{x}/\mathrm{Al}

Cooper-pair box charge qubit. With our device, we find a strong correlation between the lifetime of the qubit and the inverse of the coupling between the qubit and the transmission line. At the smallest coupling we measured, the lifetime of the Cooper-pair box was ${T}_{1}=200\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$, which represents more than a twentyfold improvement in the lifetime of the Cooper-pair box compared with previous results. These results imply that the loss tangent in the

{\mathrm{AlO}}_{x}

junction barrier must be less than about $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ at 4.5 GHz, about 4 orders of magnitude less than reported in larger area

\mathrm{Al}/{\mathrm{AlO}}_{x}/\mathrm{Al}

tunnel junctions.