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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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t yamamoto yu a pashkin o astafiev y nakamura j s tsai
T. Yamamoto, Yu. A. Pashkin, O. Astafiev, Y. Nakamura & J. S. TsaiDemonstration of conditional gate operation using superconducting charge qubits

Presented by Martin Stattin and Vincent Peikert

index
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
1 introduction the one qubit system
1: Introduction

The one qubit system

1 1 josephson junction
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
1 2 hamiltonian
1.2 Hamiltonian
  • Parabolar shape of the
  • electric energy
  • Josephson energy as a
  • coupling between charge
  • states
  • => Charge is no
  • good quantum number
  • anymore !
1 3 energy band with e j 0
1.3 Energy band with EJ = 0
  • Charge as a good quantum number
  • Degeneracy points
  • => no energy needed to tunnel to the box
1 3 energy bands with e j 0
1.3 Energy bands with EJ = 0

Change the quantum number

from charge to energy !

1 4 energy band with e j 0
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)
1 5 magnetic flux
1.5 Magnetic flux

=>

The Josephson energy

is a function of the

magnetic flux !

3 1 truth table
3.1 Truth table
  • Implementation of CNOT operation succeeded !

=> compare data with simulation data

3 2 data discussion
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
3 3 possible improvements
3.3 Possible improvements
  • Increasing Em
  • Decrease the
  • raise/fall time of
  • the pulse by 25 %
  • => red lines
source list
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
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