Observation of Entanglement between a superconducting qubit and an itinerant microwave field

Christopher Eichler

co-authors: C. Lang, J. Fink, S. Filipp, A. Wallraff

Department of Physics, ETH Zurich

The generation of entanglement between stationary qubits and propagating photons both enables the study of non-local effects in quantum mechanics and provides a resource for communication between different nodes in a quantum network.  Qubit - photon entanglement has so far only been implemented at optical frequencies with single atoms or electron spins.  Recent progress in the development of superconducting qubits and in the characterization of propagating microwave fields has also enabled exciting new quantum optics experiments using microwaves.  Here, we present experiments in which we prepare and reconstruct the state of non-classical microwave fields by combining novel photon field characterization methods with efficient measurement techniques. We also demonstrate the generation of entangled states between a superconducting qubit and a photon field. Extracting all relevant correlations between the two systems we are able to reconstruct the full density matrix and to verify the entanglement of Bell type states and more complex ones.