Journal of Low Temperature Physics

, Volume 146, Issue 1–2, pp 227–252 | Cite as

Dispersive Charge and Flux Qubit Readout as a Quantum Measurement Process

  • Lars Tornberg
  • Göran Johansson

We analyze the dispersive readout of superconducting charge and flux qubits as a quantum measurement process. The measurement oscillator frequency is considered much lower than the qubit frequency. This regime is interesting because large detuning allows for strong coupling between the measurement oscillator and the signal transmission line, thus allowing for fast readout. Due to the large detuning we may not use the rotating wave approximation in the oscillator-qubit coupling. Instead we start from an approximation where the qubit follows the oscillator adiabatically, and show that non-adiabatic corrections are small. We find analytic expressions for the measurement time, as well as for the back-action, both while measuring and in the off-state. The quantum efficiency is found to be unity within our approximation, both for charge and flux qubit readout.


uantum computing quantum measurements superconducting qubits quantum electrical circuits single Cooper-pair box 

PACS Numbers

74.50.+r 03.65.-w 03.67.Lx 42.50.Lc 


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Copyright information

© Springer Science+Business Media, LLC 2006

Authors and Affiliations

  1. 1.Applied Quantum PhysicsGöteborgSweden

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