Dynamics of dispersive single-qubit readout in circuit quantum electrodynamics Journal Article

Author(s): Bianchetti, R; Filipp, Stefan; Baur, Matthias P; Fink, Johannes; Göppl, M; Leek, Peter J; Steffen, L. Kraig; Blais, Alexandre; Wallraff, Andreas
Article Title: Dynamics of dispersive single-qubit readout in circuit quantum electrodynamics
Abstract: The quantum state of a superconducting qubit nonresonantly coupled to a transmission line resonator can be determined by measuring the quadrature amplitudes of an electromagnetic field transmitted through the resonator. We present experiments in which we analyze in detail the dynamics of the transmitted field as a function of the measurement frequency for both weak continuous and pulsed measurements. We find excellent agreement between our data and calculations based on a set of Bloch-type differential equations for the cavity field derived from the dispersive Jaynes-Cummings Hamiltonian including dissipation. We show that the measured system response can be used to construct a measurement operator from which the qubit population can be inferred accurately. Such a measurement operator can be used in tomographic methods to reconstruct single and multiqubit states in ensemble-averaged measurements.
Keywords: QUANTUM ELECTRODYNAMICS; Quantum state; Electromagnetic fields; Superconducting qubits; Quantum electronics; Electrodynamics; Transmission line resonators; Resonators; Cavity field; Qubit read-out; Jaynes-Cummings Hamiltonian; Measured system; Measurement frequency; Multiqubit state; Pulsed measurements; Tomographic methods; Transmitted field; Differential equations; Mathematical operators
Journal Title: Physical Review A - Atomic, Molecular, and Optical Physics
Volume: 80
Issue 4
ISSN: 1094-1622
Publisher: American Physical Society  
Date Published: 2009-10-30
Start Page: Article number 043840
Sponsor: This work was supported by the SNF Project No. 111899 and ETH Zurich. A.B. was supported by NSERC, CIFAR, and the Alfred P. Sloan Foundation
DOI: 10.1103/PhysRevA.80.043840
Open access: yes (repository)