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Demonstration of conditional gate operation using superconducting charge qubits

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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 – PowerPoint PPT presentation

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Title: Demonstration of conditional gate operation using superconducting charge qubits


1
Demonstration of conditional gate operation using
superconducting charge qubits
  • T. Yamamoto, Yu. A. Pashkin, O. Astafiev, Y.
    Nakamura J. S. Tsai

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 ltgt 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
  • gt very precise charge tuning

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

6
1.3 Energy band with EJ 0
  • Charge as a good quantum number
  • Degeneracy points
  • gt 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 ltgt 0
  • Charge is no good quantum number
  • degeneracy points splitted up
  • Possible to reach the degeneracy point by
    applying a special pulse ! gt rabi oscillation
    ( to E)

9
1.5 Magnetic flux
gt
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 !

gt 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
  • gt 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
  • gt red lines

18
Source list
  1. 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
  2. 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
  3. Lectures on quantum information systems WS
    2006/2007, Wallraff, ETHZ

19
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