Demonstration of conditional gate operation using superconducting charge qubits

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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

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T. Yamamoto, Yu. A. Pashkin, O. Astafiev, Y. Nakamura & J. S. Tsai

Presented by Martin Stattin and Vincent Peikert

- 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

- 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

- Parabolar shape of the
- electric energy
- Josephson energy as a
- coupling between charge
- states
- => Charge is no
- good quantum number
- anymore !

- Charge as a good quantum number
- Degeneracy points
- => no energy needed to tunnel to the box

Change the quantum number

from charge to energy !

- 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)

=>

The Josephson energy

is a function of the

magnetic flux !

- 2: Experiment

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- 3: Data analysis

- Implementation of CNOT operation succeeded !

=> compare data with simulation data

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

- Increasing Em
- Decrease the
- raise/fall time of
- the pulse by 25 %
- => red lines

- 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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