Two-Qubit State Tomography Using a Joint Dispersive Readout
Stefan Filipp, Patrick Maurer, Peter Leek, Matthias Baur, R. Bianchetti, J. M. Fink, M. Göppl, L. Steffen, Jay Gambetta, Alexandre Blais, Andreas J. Wallraff · Physical Review Letters · 2009
Quantum state tomography is an important tool in quantum information science for complete characterization of multiqubit states and their correlations. Here we report a method to perform a joint simultaneous readout of two superconducting qubits dispersively coupled to the same mode of a microwave transmission line resonator. The nonlinear dependence of the resonator transmission on the qubit state dependent cavity frequency allows us to extract the full two-qubit correlations without the need for single-shot readout of individual qubits. We employ standard tomographic techniques to reconstruct the density matrix of two-qubit quantum states.