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J. Wenner,
R. Barends, R. C. Bialczak,
Yu Chen,
J. Kelly,
Erik Lucero,
Matteo Mariantoni,
A. Megrant,
P. J. J. OMalley,
D. Sank,
A. Vainsencher,
H. Wang,
T. C. White,
Y. Yin,
J. Zhao,
A. N. Cleland,
John M. Martinis
[show abstract]
[hide abstract]
ABSTRACT: Losses in superconducting planar resonators are presently assumed to predominantly arise from surface-oxide dissipation, due to experimental losses varying with choice of materials. We model and simulate the magnitude of the loss from interface surfaces in the resonator and investigate the dependence on power, resonator geometry, and dimensions. Surprisingly, the dominant surface loss is found to arise from the metal-substrate and substrate-air interfaces. This result will be useful in guiding device optimization, even with conventional materials.
Applied Physics Letters 10/2011; · 3.84 Impact Factor
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R. Barends,
J. Wenner,
M. Lenander,
Y Chen, R. C. Bialczak,
J. Kelly,
E. Lucero,
P. O'Malley,
M. Mariantoni,
D. Sank,
H Wang,
T. C. White,
Y Yin,
J Zhao,
A. N. Cleland,
John M. Martinis,
J.J.A. Baselmans
[show abstract]
[hide abstract]
ABSTRACT: We find that stray infrared light from the 4 K stage in a cryostat can cause
significant loss in superconducting resonators and qubits. For devices shielded
in only a metal box, we measured resonators with quality factors Q = 10^5 and
qubits with energy relaxation times T_1=120 ns, consistent with a stray
light-induced quasiparticle density of 170-230 \mu m^{-3}. By adding a second
black shield at the sample temperature, we found about an order of magnitude
improvement in performance and no sensitivity to the 4 K radiation. We also
tested various shielding methods, implying a lower limit of Q = 10^8 due to
stray light in the light-tight configuration.
05/2011;
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R C Bialczak,
M Ansmann,
M Hofheinz,
M Lenander,
E Lucero,
M Neeley,
A D O'Connell,
D Sank,
H Wang,
M Weides,
J Wenner,
T Yamamoto,
A N Cleland,
J M Martinis
[show abstract]
[hide abstract]
ABSTRACT: A major challenge in the field of quantum computing is the construction of scalable qubit coupling architectures. Here, we demonstrate a novel tunable coupling circuit that allows superconducting qubits to be coupled over long distances. We show that the interqubit coupling strength can be arbitrarily tuned over nanosecond time scales within a sequence that mimics actual use in an algorithm. The coupler has a measured on/off ratio of 1000. The design is self-contained and physically separate from the qubits, allowing the coupler to be used as a module to connect a variety of elements such as qubits, resonators, amplifiers, and readout circuitry over distances much larger than nearest-neighbor. Such design flexibility is likely to be useful for a scalable quantum computer.
Physical Review Letters 02/2011; 106(6):060501. · 7.37 Impact Factor
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M. Weides, R. C. Bialczak,
M. Lenander,
E. Lucero,
Matteo Mariantoni,
M. Neeley,
A. D. O'Connell,
D. Sank,
H Wang,
J. Wenner,
T Yamamoto,
Y Yin,
A. N. Cleland,
J. Martinis
[show abstract]
[hide abstract]
ABSTRACT: We have developed a novel Josephson junction geometry with minimal volume of
lossy isolation dielectric, being suitable for higher quality trilayer
junctions implemented in qubits. The junctions are based on in-situ deposited
trilayers with thermal tunnel oxide, have micron-sized areas and a low subgap
current. In qubit spectroscopy only a few avoided level crossings are observed,
and the measured relaxation time of $T_1\approx400\;\rm{nsec}$ is in good
agreement with the usual phase qubit decay time, indicating low loss due to the
additional isolation dielectric.
12/2010;
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T. Yamamoto,
M. Neeley,
E. Lucero, R. C. Bialczak,
J. Kelly,
M. Lenander,
Matteo Mariantoni,
A. D. O’Connell,
D. Sank,
H. Wang,
M. Weides,
J. Wenner,
Y. Yin,
A. N. Cleland,
John M. Martinis
[show abstract]
[hide abstract]
ABSTRACT: We experimentally demonstrate quantum process tomography of controlled-Z and controlled-NOT gates using capacitively coupled superconducting phase qubits. These gates are realized by using the |2⟩ state of the phase qubit. We obtain a process fidelity of 0.70 for the controlled phase and 0.56 for the controlled-NOT gate, with the loss of fidelity mostly due to single-qubit decoherence. The controlled-Z gate is also used to demonstrate a two-qubit Deutsch-Jozsa algorithm with a single function query.
Phys. Rev. B. 11/2010; 82(18).
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R. C. Bialczak,
M Ansmann,
M Hofheinz,
M. Lenander,
E. Lucero,
M. Neeley,
A. D. O'Connell,
D. Sank,
H Wang,
M. Weides,
J. Wenner,
T Yamamoto,
A. N. Cleland,
J. M. Martinis
[show abstract]
[hide abstract]
ABSTRACT: A major challenge in the field of quantum computing is the construction of scalable qubit coupling architectures. Here, we demonstrate a novel tuneable coupling circuit that allows superconducting qubits to be coupled over long distances. We show that the inter-qubit coupling strength can be arbitrarily tuned over nanosecond timescales within a sequence that mimics actual use in an algorithm. The coupler has a measured on/off ratio of 1000. The design is self-contained and physically separate from the qubits, allowing the coupler to be used as a module to connect a variety of elements such as qubits, resonators, amplifiers, and readout circuitry over long distances. Such design flexibility is likely to be essential for a scalable quantum computer. Comment: 9 manuscript pages, 4 manuscript figures, 3 supplementary information pages, 4 supplementary figures
07/2010;
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R. C. Bialczak,
M. Ansmann,
M. Hofheinz,
E. Lucero,
M. Neeley,
A. D,
D. Sank,
H. Wang,
J. Wenner,
M. Steffen,
A. N. Cleland,
J. M. Martinis
Nature Physics 04/2010; 6(6):409-413. · 18.97 Impact Factor
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H Wang,
M Hofheinz,
M Ansmann, R C Bialczak,
Erik Lucero,
M Neeley,
A D O'Connell,
D Sank,
M Weides,
J Wenner,
A N Cleland,
John M Martinis
[show abstract]
[hide abstract]
ABSTRACT: Quantum states inevitably decay with time into a probabilistic mixture of classical states due to their interaction with the environment and measurement instrumentation. We present the first measurement of the decoherence dynamics of complex photon states in a condensed-matter system. By controllably preparing a number of distinct quantum-superposed photon states in a superconducting microwave resonator, we show that the subsequent decay dynamics can be quantitatively described by taking into account only two distinct decay channels: energy relaxation and pure dephasing. Our ability to prepare specific initial quantum states allows us to measure the evolution of specific elements in the quantum density matrix in a very detailed manner that can be compared with theory.
Physical Review Letters 11/2009; 103(20):200404. · 7.37 Impact Factor
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H Wang,
M Hofheinz,
J. Wenner,
M Ansmann, R. C. Bialczak,
M. Lenander,
Erik Lucero,
M. Neeley,
A. D. O'Connell,
D. Sank,
M. Weides,
A. N. Cleland,
John M. Martinis
[show abstract]
[hide abstract]
ABSTRACT: The quality factor and energy decay time of superconducting resonators have been measured as a function of material, geometry, and magnetic field. Once the dissipation of trapped magnetic vortices is minimized, we identify surface two-level states (TLS) as an important decay mechanism. A wide gap between the center conductor and the ground plane, as well as use of the superconductor Re instead of Al, are shown to decrease loss. We also demonstrate that classical measurements of resonator quality factor at low excitation power are consistent with single-photon decay time measured using qubit-resonator swap experiments. Comment: 3 pages, 4 figures for the main paper; total 5 pages, 6 figures including supplementary material. Submitted to Applied Physics Letters
09/2009;
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H Wang,
M Hofheinz,
M Ansmann, R C Bialczak,
E Lucero,
M Neeley,
A D O'Connell,
D Sank,
J Wenner,
A N Cleland,
John M Martinis
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate the controlled generation of Fock states with up to 15 photons in a microwave coplanar waveguide resonator coupled to a superconducting phase qubit. The subsequent decay of the Fock states, due to dissipation, is then monitored by varying the time delay between preparing the state and performing a number-state analysis. We find that the decay dynamics can be described by a master equation where the lifetime of the n-photon Fock state scales as 1/n, in agreement with theory. We have also generated a coherent state in the microwave resonator, and monitored its decay process. We demonstrate that the coherent state maintains a Poisson distribution as it decays, with an average photon number that decreases with the same characteristic decay time as the one-photon Fock state.
Physical Review Letters 01/2009; 101(24):240401. · 7.37 Impact Factor
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Aaron D. OConnell,
M. Ansmann, R. C. Bialczak,
M. Hofheinz,
N. Katz,
Erik Lucero,
C. McKenney,
M. Neeley,
H. Wang,
E. M. Weig,
A. N. Cleland,
J. M. Martinis
[show abstract]
[hide abstract]
ABSTRACT: The microwave performance of amorphous dielectric materials at very low temperatures and very low excitation strengths displays significant excess loss. Here, we present the loss tangents of some common amorphous and crystalline dielectrics, measured at low temperatures (T≪100 mK ) with near single-photon excitation energies, E/ħω<sub>0</sub>∼1 , using both coplanar waveguide and lumped LC resonators. The loss can be understood using a two-level state defect model. A circuit analysis of the half-wavelength resonators we used is outlined, and the energy dissipation of such a resonator on a multilayered dielectric substrate is theoretically considered.
Applied Physics Letters 04/2008; · 3.84 Impact Factor
