Dispersive charge and flux qubit readout as a quantum measurement process

Lars Tornberg*, Göran Johansson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)227-252
Number of pages26
JournalJournal of Low Temperature Physics
Issue number1-2
StatePublished - Jan 2007
Externally publishedYes


  • Quantum computing
  • Quantum electrical circuits
  • Quantum measurements
  • Single Cooper-pair box
  • Superconducting qubits


Dive into the research topics of 'Dispersive charge and flux qubit readout as a quantum measurement process'. Together they form a unique fingerprint.

Cite this