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Demonstration of conditional gate operation using superconducting charge qubits

T. Yamamoto, Yu. A. Pashkin, O. Astafiev, Y. Nakamura & J. S. Tsai. Demonstration of conditional gate operation using superconducting charge qubits. Presented by Martin Stattin and Vincent Peikert. Index. 1 Introduction: The one qubit system 1.1 Josephson Junction 1.2 Hamiltonian

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Demonstration of conditional gate operation using superconducting charge qubits

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  1. T. Yamamoto, Yu. A. Pashkin, O. Astafiev, Y. Nakamura & J. S. Tsai Demonstration of conditional gate operation using superconducting charge qubits Presented by Martin Stattin and Vincent Peikert

  2. Index • 1 Introduction: The one qubit system • 1.1 Josephson Junction • 1.2 Hamiltonian • 1.3 Energy bands with EJ = 0 • 1.4 Energy bands with EJ <> 0 • 2 Experiment • 2.1 Experiment setup • 2.2 Experiment • 2.3 Results • 3 Data analysis • 3.1 Truth table • 3.2 Data disscussion • 3.3 Improvements

  3. 1: Introduction The one qubit system

  4. 1.1 Josephson Junction • Behaves like a circuit with • capacitance and • inhomogenous inductor • Josephson energy • responsible for coherent • tunneling • Superconducting elements • Gate electrode in our case • also superconducting • => very precise charge tuning

  5. 1.2 Hamiltonian • Parabolar shape of the • electric energy • Josephson energy as a • coupling between charge • states • => Charge is no • good quantum number • anymore !

  6. 1.3 Energy band with EJ = 0 • Charge as a good quantum number • Degeneracy points • => no energy needed to tunnel to the box

  7. 1.3 Energy bands with EJ = 0 Change the quantum number from charge to energy !

  8. 1.4 Energy band with EJ <> 0 • Charge is no good quantum number • degeneracy points splitted up • Possible to reach the degeneracy point by applying a special pulse ! => rabi oscillation (~ to E)

  9. 1.5 Magnetic flux => The Josephson energy is a function of the magnetic flux !

  10. 2: Experiment

  11. 2.1 Experiment setup [1] [2]

  12. 2.2 Experiment [1]

  13. 2.3 Results [1] [1]

  14. 3: Data analysis

  15. 3.1 Truth table • Implementation of CNOT operation succeeded ! => compare data with simulation data

  16. 3.2 Data discussion Numerical calculation of the density matrix's time evolution • Target qubit: • good agreement with the • experiment (but a little offset) • Control qubit: • Discrepency due to the unknown • currend channel in the readout • scheme • Pulse induced currend should not • exceed 2.4 pA but it does • => currend has an extra component • maybe from higher order • Cooper-pair tunnerling

  17. 3.3 Possible improvements • Increasing Em • Decrease the • raise/fall time of • the pulse by 25 % • => red lines

  18. Source list • T. Yamamoto, Yu. A. Pashkin, O. Astafiev, Y. Nakamura & J. S. Tsai, ”Demonstration of conditional gate operation using superconducting charge qubits”, Nature, Vol 425, pp 941-944, oct 2003 • Yu. A. Pashkin, T. Yamamoto, O. Astafiev, Y. Nakamura, D. Averin & J. S. Tsai, ”Coupling two charge qubits”, NEC Res. and Develop., Vol 44, no 3, pp 273-277, jul 2003 • Lectures on quantum information systems WS 2006/2007, Wallraff, ETHZ

  19. [2]

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